Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3536 insertions, 0 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
new file mode 100644
index 000000000..3b0d8c6dd
--- /dev/null
+++ b/mm/filemap.c
@@ -0,0 +1,3536 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *	linux/mm/filemap.c
+ *
+ * Copyright (C) 1994-1999  Linus Torvalds
+ */
+
+/*
+ * This file handles the generic file mmap semantics used by
+ * most "normal" filesystems (but you don't /have/ to use this:
+ * the NFS filesystem used to do this differently, for example)
+ */
+#include <linux/export.h>
+#include <linux/compiler.h>
+#include <linux/dax.h>
+#include <linux/fs.h>
+#include <linux/sched/signal.h>
+#include <linux/uaccess.h>
+#include <linux/capability.h>
+#include <linux/kernel_stat.h>
+#include <linux/gfp.h>
+#include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/mman.h>
+#include <linux/pagemap.h>
+#include <linux/file.h>
+#include <linux/uio.h>
+#include <linux/error-injection.h>
+#include <linux/hash.h>
+#include <linux/writeback.h>
+#include <linux/backing-dev.h>
+#include <linux/pagevec.h>
+#include <linux/blkdev.h>
+#include <linux/security.h>
+#include <linux/cpuset.h>
+#include <linux/hugetlb.h>
+#include <linux/memcontrol.h>
+#include <linux/cleancache.h>
+#include <linux/shmem_fs.h>
+#include <linux/rmap.h>
+#include <linux/delayacct.h>
+#include <linux/psi.h>
+#include <linux/ramfs.h>
+#include <linux/page_idle.h>
+#include "internal.h"
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/filemap.h>
+
+/*
+ * FIXME: remove all knowledge of the buffer layer from the core VM
+ */
+#include <linux/buffer_head.h> /* for try_to_free_buffers */
+
+#include <asm/mman.h>
+
+/*
+ * Shared mappings implemented 30.11.1994. It's not fully working yet,
+ * though.
+ *
+ * Shared mappings now work. 15.8.1995  Bruno.
+ *
+ * finished 'unifying' the page and buffer cache and SMP-threaded the
+ * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
+ *
+ * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
+ */
+
+/*
+ * Lock ordering:
+ *
+ *  ->i_mmap_rwsem		(truncate_pagecache)
+ *    ->private_lock		(__free_pte->__set_page_dirty_buffers)
+ *      ->swap_lock		(exclusive_swap_page, others)
+ *        ->i_pages lock
+ *
+ *  ->i_mutex
+ *    ->i_mmap_rwsem		(truncate->unmap_mapping_range)
+ *
+ *  ->mmap_lock
+ *    ->i_mmap_rwsem
+ *      ->page_table_lock or pte_lock	(various, mainly in memory.c)
+ *        ->i_pages lock	(arch-dependent flush_dcache_mmap_lock)
+ *
+ *  ->mmap_lock
+ *    ->lock_page		(access_process_vm)
+ *
+ *  ->i_mutex			(generic_perform_write)
+ *    ->mmap_lock		(fault_in_pages_readable->do_page_fault)
+ *
+ *  bdi->wb.list_lock
+ *    sb_lock			(fs/fs-writeback.c)
+ *    ->i_pages lock		(__sync_single_inode)
+ *
+ *  ->i_mmap_rwsem
+ *    ->anon_vma.lock		(vma_adjust)
+ *
+ *  ->anon_vma.lock
+ *    ->page_table_lock or pte_lock	(anon_vma_prepare and various)
+ *
+ *  ->page_table_lock or pte_lock
+ *    ->swap_lock		(try_to_unmap_one)
+ *    ->private_lock		(try_to_unmap_one)
+ *    ->i_pages lock		(try_to_unmap_one)
+ *    ->pgdat->lru_lock		(follow_page->mark_page_accessed)
+ *    ->pgdat->lru_lock		(check_pte_range->isolate_lru_page)
+ *    ->private_lock		(page_remove_rmap->set_page_dirty)
+ *    ->i_pages lock		(page_remove_rmap->set_page_dirty)
+ *    bdi.wb->list_lock		(page_remove_rmap->set_page_dirty)
+ *    ->inode->i_lock		(page_remove_rmap->set_page_dirty)
+ *    ->memcg->move_lock	(page_remove_rmap->lock_page_memcg)
+ *    bdi.wb->list_lock		(zap_pte_range->set_page_dirty)
+ *    ->inode->i_lock		(zap_pte_range->set_page_dirty)
+ *    ->private_lock		(zap_pte_range->__set_page_dirty_buffers)
+ *
+ * ->i_mmap_rwsem
+ *   ->tasklist_lock            (memory_failure, collect_procs_ao)
+ */
+
+static void page_cache_delete(struct address_space *mapping,
+				   struct page *page, void *shadow)
+{
+	XA_STATE(xas, &mapping->i_pages, page->index);
+	unsigned int nr = 1;
+
+	mapping_set_update(&xas, mapping);
+
+	/* hugetlb pages are represented by a single entry in the xarray */
+	if (!PageHuge(page)) {
+		xas_set_order(&xas, page->index, compound_order(page));
+		nr = compound_nr(page);
+	}
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(PageTail(page), page);
+	VM_BUG_ON_PAGE(nr != 1 && shadow, page);
+
+	xas_store(&xas, shadow);
+	xas_init_marks(&xas);
+
+	page->mapping = NULL;
+	/* Leave page->index set: truncation lookup relies upon it */
+
+	if (shadow) {
+		mapping->nrexceptional += nr;
+		/*
+		 * Make sure the nrexceptional update is committed before
+		 * the nrpages update so that final truncate racing
+		 * with reclaim does not see both counters 0 at the
+		 * same time and miss a shadow entry.
+		 */
+		smp_wmb();
+	}
+	mapping->nrpages -= nr;
+}
+
+static void unaccount_page_cache_page(struct address_space *mapping,
+				      struct page *page)
+{
+	int nr;
+
+	/*
+	 * if we're uptodate, flush out into the cleancache, otherwise
+	 * invalidate any existing cleancache entries.  We can't leave
+	 * stale data around in the cleancache once our page is gone
+	 */
+	if (PageUptodate(page) && PageMappedToDisk(page))
+		cleancache_put_page(page);
+	else
+		cleancache_invalidate_page(mapping, page);
+
+	VM_BUG_ON_PAGE(PageTail(page), page);
+	VM_BUG_ON_PAGE(page_mapped(page), page);
+	if (!IS_ENABLED(CONFIG_DEBUG_VM) && unlikely(page_mapped(page))) {
+		int mapcount;
+
+		pr_alert("BUG: Bad page cache in process %s  pfn:%05lx\n",
+			 current->comm, page_to_pfn(page));
+		dump_page(page, "still mapped when deleted");
+		dump_stack();
+		add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
+
+		mapcount = page_mapcount(page);
+		if (mapping_exiting(mapping) &&
+		    page_count(page) >= mapcount + 2) {
+			/*
+			 * All vmas have already been torn down, so it's
+			 * a good bet that actually the page is unmapped,
+			 * and we'd prefer not to leak it: if we're wrong,
+			 * some other bad page check should catch it later.
+			 */
+			page_mapcount_reset(page);
+			page_ref_sub(page, mapcount);
+		}
+	}
+
+	/* hugetlb pages do not participate in page cache accounting. */
+	if (PageHuge(page))
+		return;
+
+	nr = thp_nr_pages(page);
+
+	__mod_lruvec_page_state(page, NR_FILE_PAGES, -nr);
+	if (PageSwapBacked(page)) {
+		__mod_lruvec_page_state(page, NR_SHMEM, -nr);
+		if (PageTransHuge(page))
+			__dec_node_page_state(page, NR_SHMEM_THPS);
+	} else if (PageTransHuge(page)) {
+		__dec_node_page_state(page, NR_FILE_THPS);
+		filemap_nr_thps_dec(mapping);
+	}
+
+	/*
+	 * At this point page must be either written or cleaned by
+	 * truncate.  Dirty page here signals a bug and loss of
+	 * unwritten data.
+	 *
+	 * This fixes dirty accounting after removing the page entirely
+	 * but leaves PageDirty set: it has no effect for truncated
+	 * page and anyway will be cleared before returning page into
+	 * buddy allocator.
+	 */
+	if (WARN_ON_ONCE(PageDirty(page)))
+		account_page_cleaned(page, mapping, inode_to_wb(mapping->host));
+}
+
+/*
+ * Delete a page from the page cache and free it. Caller has to make
+ * sure the page is locked and that nobody else uses it - or that usage
+ * is safe.  The caller must hold the i_pages lock.
+ */
+void __delete_from_page_cache(struct page *page, void *shadow)
+{
+	struct address_space *mapping = page->mapping;
+
+	trace_mm_filemap_delete_from_page_cache(page);
+
+	unaccount_page_cache_page(mapping, page);
+	page_cache_delete(mapping, page, shadow);
+}
+
+static void page_cache_free_page(struct address_space *mapping,
+				struct page *page)
+{
+	void (*freepage)(struct page *);
+
+	freepage = mapping->a_ops->freepage;
+	if (freepage)
+		freepage(page);
+
+	if (PageTransHuge(page) && !PageHuge(page)) {
+		page_ref_sub(page, thp_nr_pages(page));
+		VM_BUG_ON_PAGE(page_count(page) <= 0, page);
+	} else {
+		put_page(page);
+	}
+}
+
+/**
+ * delete_from_page_cache - delete page from page cache
+ * @page: the page which the kernel is trying to remove from page cache
+ *
+ * This must be called only on pages that have been verified to be in the page
+ * cache and locked.  It will never put the page into the free list, the caller
+ * has a reference on the page.
+ */
+void delete_from_page_cache(struct page *page)
+{
+	struct address_space *mapping = page_mapping(page);
+	unsigned long flags;
+
+	BUG_ON(!PageLocked(page));
+	xa_lock_irqsave(&mapping->i_pages, flags);
+	__delete_from_page_cache(page, NULL);
+	xa_unlock_irqrestore(&mapping->i_pages, flags);
+
+	page_cache_free_page(mapping, page);
+}
+EXPORT_SYMBOL(delete_from_page_cache);
+
+/*
+ * page_cache_delete_batch - delete several pages from page cache
+ * @mapping: the mapping to which pages belong
+ * @pvec: pagevec with pages to delete
+ *
+ * The function walks over mapping->i_pages and removes pages passed in @pvec
+ * from the mapping. The function expects @pvec to be sorted by page index
+ * and is optimised for it to be dense.
+ * It tolerates holes in @pvec (mapping entries at those indices are not
+ * modified). The function expects only THP head pages to be present in the
+ * @pvec.
+ *
+ * The function expects the i_pages lock to be held.
+ */
+static void page_cache_delete_batch(struct address_space *mapping,
+			     struct pagevec *pvec)
+{
+	XA_STATE(xas, &mapping->i_pages, pvec->pages[0]->index);
+	int total_pages = 0;
+	int i = 0;
+	struct page *page;
+
+	mapping_set_update(&xas, mapping);
+	xas_for_each(&xas, page, ULONG_MAX) {
+		if (i >= pagevec_count(pvec))
+			break;
+
+		/* A swap/dax/shadow entry got inserted? Skip it. */
+		if (xa_is_value(page))
+			continue;
+		/*
+		 * A page got inserted in our range? Skip it. We have our
+		 * pages locked so they are protected from being removed.
+		 * If we see a page whose index is higher than ours, it
+		 * means our page has been removed, which shouldn't be
+		 * possible because we're holding the PageLock.
+		 */
+		if (page != pvec->pages[i]) {
+			VM_BUG_ON_PAGE(page->index > pvec->pages[i]->index,
+					page);
+			continue;
+		}
+
+		WARN_ON_ONCE(!PageLocked(page));
+
+		if (page->index == xas.xa_index)
+			page->mapping = NULL;
+		/* Leave page->index set: truncation lookup relies on it */
+
+		/*
+		 * Move to the next page in the vector if this is a regular
+		 * page or the index is of the last sub-page of this compound
+		 * page.
+		 */
+		if (page->index + compound_nr(page) - 1 == xas.xa_index)
+			i++;
+		xas_store(&xas, NULL);
+		total_pages++;
+	}
+	mapping->nrpages -= total_pages;
+}
+
+void delete_from_page_cache_batch(struct address_space *mapping,
+				  struct pagevec *pvec)
+{
+	int i;
+	unsigned long flags;
+
+	if (!pagevec_count(pvec))
+		return;
+
+	xa_lock_irqsave(&mapping->i_pages, flags);
+	for (i = 0; i < pagevec_count(pvec); i++) {
+		trace_mm_filemap_delete_from_page_cache(pvec->pages[i]);
+
+		unaccount_page_cache_page(mapping, pvec->pages[i]);
+	}
+	page_cache_delete_batch(mapping, pvec);
+	xa_unlock_irqrestore(&mapping->i_pages, flags);
+
+	for (i = 0; i < pagevec_count(pvec); i++)
+		page_cache_free_page(mapping, pvec->pages[i]);
+}
+
+int filemap_check_errors(struct address_space *mapping)
+{
+	int ret = 0;
+	/* Check for outstanding write errors */
+	if (test_bit(AS_ENOSPC, &mapping->flags) &&
+	    test_and_clear_bit(AS_ENOSPC, &mapping->flags))
+		ret = -ENOSPC;
+	if (test_bit(AS_EIO, &mapping->flags) &&
+	    test_and_clear_bit(AS_EIO, &mapping->flags))
+		ret = -EIO;
+	return ret;
+}
+EXPORT_SYMBOL(filemap_check_errors);
+
+static int filemap_check_and_keep_errors(struct address_space *mapping)
+{
+	/* Check for outstanding write errors */
+	if (test_bit(AS_EIO, &mapping->flags))
+		return -EIO;
+	if (test_bit(AS_ENOSPC, &mapping->flags))
+		return -ENOSPC;
+	return 0;
+}
+
+/**
+ * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
+ * @mapping:	address space structure to write
+ * @start:	offset in bytes where the range starts
+ * @end:	offset in bytes where the range ends (inclusive)
+ * @sync_mode:	enable synchronous operation
+ *
+ * Start writeback against all of a mapping's dirty pages that lie
+ * within the byte offsets <start, end> inclusive.
+ *
+ * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
+ * opposed to a regular memory cleansing writeback.  The difference between
+ * these two operations is that if a dirty page/buffer is encountered, it must
+ * be waited upon, and not just skipped over.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
+				loff_t end, int sync_mode)
+{
+	int ret;
+	struct writeback_control wbc = {
+		.sync_mode = sync_mode,
+		.nr_to_write = LONG_MAX,
+		.range_start = start,
+		.range_end = end,
+	};
+
+	if (!mapping_can_writeback(mapping) ||
+	    !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
+		return 0;
+
+	wbc_attach_fdatawrite_inode(&wbc, mapping->host);
+	ret = do_writepages(mapping, &wbc);
+	wbc_detach_inode(&wbc);
+	return ret;
+}
+
+static inline int __filemap_fdatawrite(struct address_space *mapping,
+	int sync_mode)
+{
+	return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
+}
+
+int filemap_fdatawrite(struct address_space *mapping)
+{
+	return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
+}
+EXPORT_SYMBOL(filemap_fdatawrite);
+
+int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
+				loff_t end)
+{
+	return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
+}
+EXPORT_SYMBOL(filemap_fdatawrite_range);
+
+/**
+ * filemap_flush - mostly a non-blocking flush
+ * @mapping:	target address_space
+ *
+ * This is a mostly non-blocking flush.  Not suitable for data-integrity
+ * purposes - I/O may not be started against all dirty pages.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int filemap_flush(struct address_space *mapping)
+{
+	return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
+}
+EXPORT_SYMBOL(filemap_flush);
+
+/**
+ * filemap_range_has_page - check if a page exists in range.
+ * @mapping:           address space within which to check
+ * @start_byte:        offset in bytes where the range starts
+ * @end_byte:          offset in bytes where the range ends (inclusive)
+ *
+ * Find at least one page in the range supplied, usually used to check if
+ * direct writing in this range will trigger a writeback.
+ *
+ * Return: %true if at least one page exists in the specified range,
+ * %false otherwise.
+ */
+bool filemap_range_has_page(struct address_space *mapping,
+			   loff_t start_byte, loff_t end_byte)
+{
+	struct page *page;
+	XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
+	pgoff_t max = end_byte >> PAGE_SHIFT;
+
+	if (end_byte < start_byte)
+		return false;
+
+	rcu_read_lock();
+	for (;;) {
+		page = xas_find(&xas, max);
+		if (xas_retry(&xas, page))
+			continue;
+		/* Shadow entries don't count */
+		if (xa_is_value(page))
+			continue;
+		/*
+		 * We don't need to try to pin this page; we're about to
+		 * release the RCU lock anyway.  It is enough to know that
+		 * there was a page here recently.
+		 */
+		break;
+	}
+	rcu_read_unlock();
+
+	return page != NULL;
+}
+EXPORT_SYMBOL(filemap_range_has_page);
+
+static void __filemap_fdatawait_range(struct address_space *mapping,
+				     loff_t start_byte, loff_t end_byte)
+{
+	pgoff_t index = start_byte >> PAGE_SHIFT;
+	pgoff_t end = end_byte >> PAGE_SHIFT;
+	struct pagevec pvec;
+	int nr_pages;
+
+	if (end_byte < start_byte)
+		return;
+
+	pagevec_init(&pvec);
+	while (index <= end) {
+		unsigned i;
+
+		nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index,
+				end, PAGECACHE_TAG_WRITEBACK);
+		if (!nr_pages)
+			break;
+
+		for (i = 0; i < nr_pages; i++) {
+			struct page *page = pvec.pages[i];
+
+			wait_on_page_writeback(page);
+			ClearPageError(page);
+		}
+		pagevec_release(&pvec);
+		cond_resched();
+	}
+}
+
+/**
+ * filemap_fdatawait_range - wait for writeback to complete
+ * @mapping:		address space structure to wait for
+ * @start_byte:		offset in bytes where the range starts
+ * @end_byte:		offset in bytes where the range ends (inclusive)
+ *
+ * Walk the list of under-writeback pages of the given address space
+ * in the given range and wait for all of them.  Check error status of
+ * the address space and return it.
+ *
+ * Since the error status of the address space is cleared by this function,
+ * callers are responsible for checking the return value and handling and/or
+ * reporting the error.
+ *
+ * Return: error status of the address space.
+ */
+int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
+			    loff_t end_byte)
+{
+	__filemap_fdatawait_range(mapping, start_byte, end_byte);
+	return filemap_check_errors(mapping);
+}
+EXPORT_SYMBOL(filemap_fdatawait_range);
+
+/**
+ * filemap_fdatawait_range_keep_errors - wait for writeback to complete
+ * @mapping:		address space structure to wait for
+ * @start_byte:		offset in bytes where the range starts
+ * @end_byte:		offset in bytes where the range ends (inclusive)
+ *
+ * Walk the list of under-writeback pages of the given address space in the
+ * given range and wait for all of them.  Unlike filemap_fdatawait_range(),
+ * this function does not clear error status of the address space.
+ *
+ * Use this function if callers don't handle errors themselves.  Expected
+ * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
+ * fsfreeze(8)
+ */
+int filemap_fdatawait_range_keep_errors(struct address_space *mapping,
+		loff_t start_byte, loff_t end_byte)
+{
+	__filemap_fdatawait_range(mapping, start_byte, end_byte);
+	return filemap_check_and_keep_errors(mapping);
+}
+EXPORT_SYMBOL(filemap_fdatawait_range_keep_errors);
+
+/**
+ * file_fdatawait_range - wait for writeback to complete
+ * @file:		file pointing to address space structure to wait for
+ * @start_byte:		offset in bytes where the range starts
+ * @end_byte:		offset in bytes where the range ends (inclusive)
+ *
+ * Walk the list of under-writeback pages of the address space that file
+ * refers to, in the given range and wait for all of them.  Check error
+ * status of the address space vs. the file->f_wb_err cursor and return it.
+ *
+ * Since the error status of the file is advanced by this function,
+ * callers are responsible for checking the return value and handling and/or
+ * reporting the error.
+ *
+ * Return: error status of the address space vs. the file->f_wb_err cursor.
+ */
+int file_fdatawait_range(struct file *file, loff_t start_byte, loff_t end_byte)
+{
+	struct address_space *mapping = file->f_mapping;
+
+	__filemap_fdatawait_range(mapping, start_byte, end_byte);
+	return file_check_and_advance_wb_err(file);
+}
+EXPORT_SYMBOL(file_fdatawait_range);
+
+/**
+ * filemap_fdatawait_keep_errors - wait for writeback without clearing errors
+ * @mapping: address space structure to wait for
+ *
+ * Walk the list of under-writeback pages of the given address space
+ * and wait for all of them.  Unlike filemap_fdatawait(), this function
+ * does not clear error status of the address space.
+ *
+ * Use this function if callers don't handle errors themselves.  Expected
+ * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
+ * fsfreeze(8)
+ *
+ * Return: error status of the address space.
+ */
+int filemap_fdatawait_keep_errors(struct address_space *mapping)
+{
+	__filemap_fdatawait_range(mapping, 0, LLONG_MAX);
+	return filemap_check_and_keep_errors(mapping);
+}
+EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
+
+/* Returns true if writeback might be needed or already in progress. */
+static bool mapping_needs_writeback(struct address_space *mapping)
+{
+	if (dax_mapping(mapping))
+		return mapping->nrexceptional;
+
+	return mapping->nrpages;
+}
+
+/**
+ * filemap_write_and_wait_range - write out & wait on a file range
+ * @mapping:	the address_space for the pages
+ * @lstart:	offset in bytes where the range starts
+ * @lend:	offset in bytes where the range ends (inclusive)
+ *
+ * Write out and wait upon file offsets lstart->lend, inclusive.
+ *
+ * Note that @lend is inclusive (describes the last byte to be written) so
+ * that this function can be used to write to the very end-of-file (end = -1).
+ *
+ * Return: error status of the address space.
+ */
+int filemap_write_and_wait_range(struct address_space *mapping,
+				 loff_t lstart, loff_t lend)
+{
+	int err = 0;
+
+	if (mapping_needs_writeback(mapping)) {
+		err = __filemap_fdatawrite_range(mapping, lstart, lend,
+						 WB_SYNC_ALL);
+		/*
+		 * Even if the above returned error, the pages may be
+		 * written partially (e.g. -ENOSPC), so we wait for it.
+		 * But the -EIO is special case, it may indicate the worst
+		 * thing (e.g. bug) happened, so we avoid waiting for it.
+		 */
+		if (err != -EIO) {
+			int err2 = filemap_fdatawait_range(mapping,
+						lstart, lend);
+			if (!err)
+				err = err2;
+		} else {
+			/* Clear any previously stored errors */
+			filemap_check_errors(mapping);
+		}
+	} else {
+		err = filemap_check_errors(mapping);
+	}
+	return err;
+}
+EXPORT_SYMBOL(filemap_write_and_wait_range);
+
+void __filemap_set_wb_err(struct address_space *mapping, int err)
+{
+	errseq_t eseq = errseq_set(&mapping->wb_err, err);
+
+	trace_filemap_set_wb_err(mapping, eseq);
+}
+EXPORT_SYMBOL(__filemap_set_wb_err);
+
+/**
+ * file_check_and_advance_wb_err - report wb error (if any) that was previously
+ * 				   and advance wb_err to current one
+ * @file: struct file on which the error is being reported
+ *
+ * When userland calls fsync (or something like nfsd does the equivalent), we
+ * want to report any writeback errors that occurred since the last fsync (or
+ * since the file was opened if there haven't been any).
+ *
+ * Grab the wb_err from the mapping. If it matches what we have in the file,
+ * then just quickly return 0. The file is all caught up.
+ *
+ * If it doesn't match, then take the mapping value, set the "seen" flag in
+ * it and try to swap it into place. If it works, or another task beat us
+ * to it with the new value, then update the f_wb_err and return the error
+ * portion. The error at this point must be reported via proper channels
+ * (a'la fsync, or NFS COMMIT operation, etc.).
+ *
+ * While we handle mapping->wb_err with atomic operations, the f_wb_err
+ * value is protected by the f_lock since we must ensure that it reflects
+ * the latest value swapped in for this file descriptor.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int file_check_and_advance_wb_err(struct file *file)
+{
+	int err = 0;
+	errseq_t old = READ_ONCE(file->f_wb_err);
+	struct address_space *mapping = file->f_mapping;
+
+	/* Locklessly handle the common case where nothing has changed */
+	if (errseq_check(&mapping->wb_err, old)) {
+		/* Something changed, must use slow path */
+		spin_lock(&file->f_lock);
+		old = file->f_wb_err;
+		err = errseq_check_and_advance(&mapping->wb_err,
+						&file->f_wb_err);
+		trace_file_check_and_advance_wb_err(file, old);
+		spin_unlock(&file->f_lock);
+	}
+
+	/*
+	 * We're mostly using this function as a drop in replacement for
+	 * filemap_check_errors. Clear AS_EIO/AS_ENOSPC to emulate the effect
+	 * that the legacy code would have had on these flags.
+	 */
+	clear_bit(AS_EIO, &mapping->flags);
+	clear_bit(AS_ENOSPC, &mapping->flags);
+	return err;
+}
+EXPORT_SYMBOL(file_check_and_advance_wb_err);
+
+/**
+ * file_write_and_wait_range - write out & wait on a file range
+ * @file:	file pointing to address_space with pages
+ * @lstart:	offset in bytes where the range starts
+ * @lend:	offset in bytes where the range ends (inclusive)
+ *
+ * Write out and wait upon file offsets lstart->lend, inclusive.
+ *
+ * Note that @lend is inclusive (describes the last byte to be written) so
+ * that this function can be used to write to the very end-of-file (end = -1).
+ *
+ * After writing out and waiting on the data, we check and advance the
+ * f_wb_err cursor to the latest value, and return any errors detected there.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int file_write_and_wait_range(struct file *file, loff_t lstart, loff_t lend)
+{
+	int err = 0, err2;
+	struct address_space *mapping = file->f_mapping;
+
+	if (mapping_needs_writeback(mapping)) {
+		err = __filemap_fdatawrite_range(mapping, lstart, lend,
+						 WB_SYNC_ALL);
+		/* See comment of filemap_write_and_wait() */
+		if (err != -EIO)
+			__filemap_fdatawait_range(mapping, lstart, lend);
+	}
+	err2 = file_check_and_advance_wb_err(file);
+	if (!err)
+		err = err2;
+	return err;
+}
+EXPORT_SYMBOL(file_write_and_wait_range);
+
+/**
+ * replace_page_cache_page - replace a pagecache page with a new one
+ * @old:	page to be replaced
+ * @new:	page to replace with
+ * @gfp_mask:	allocation mode
+ *
+ * This function replaces a page in the pagecache with a new one.  On
+ * success it acquires the pagecache reference for the new page and
+ * drops it for the old page.  Both the old and new pages must be
+ * locked.  This function does not add the new page to the LRU, the
+ * caller must do that.
+ *
+ * The remove + add is atomic.  This function cannot fail.
+ *
+ * Return: %0
+ */
+int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
+{
+	struct address_space *mapping = old->mapping;
+	void (*freepage)(struct page *) = mapping->a_ops->freepage;
+	pgoff_t offset = old->index;
+	XA_STATE(xas, &mapping->i_pages, offset);
+	unsigned long flags;
+
+	VM_BUG_ON_PAGE(!PageLocked(old), old);
+	VM_BUG_ON_PAGE(!PageLocked(new), new);
+	VM_BUG_ON_PAGE(new->mapping, new);
+
+	get_page(new);
+	new->mapping = mapping;
+	new->index = offset;
+
+	mem_cgroup_migrate(old, new);
+
+	xas_lock_irqsave(&xas, flags);
+	xas_store(&xas, new);
+
+	old->mapping = NULL;
+	/* hugetlb pages do not participate in page cache accounting. */
+	if (!PageHuge(old))
+		__dec_lruvec_page_state(old, NR_FILE_PAGES);
+	if (!PageHuge(new))
+		__inc_lruvec_page_state(new, NR_FILE_PAGES);
+	if (PageSwapBacked(old))
+		__dec_lruvec_page_state(old, NR_SHMEM);
+	if (PageSwapBacked(new))
+		__inc_lruvec_page_state(new, NR_SHMEM);
+	xas_unlock_irqrestore(&xas, flags);
+	if (freepage)
+		freepage(old);
+	put_page(old);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(replace_page_cache_page);
+
+noinline int __add_to_page_cache_locked(struct page *page,
+					struct address_space *mapping,
+					pgoff_t offset, gfp_t gfp,
+					void **shadowp)
+{
+	XA_STATE(xas, &mapping->i_pages, offset);
+	int huge = PageHuge(page);
+	int error;
+	bool charged = false;
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE(PageSwapBacked(page), page);
+	mapping_set_update(&xas, mapping);
+
+	get_page(page);
+	page->mapping = mapping;
+	page->index = offset;
+
+	if (!huge) {
+		error = mem_cgroup_charge(page, current->mm, gfp);
+		if (error)
+			goto error;
+		charged = true;
+	}
+
+	gfp &= GFP_RECLAIM_MASK;
+
+	do {
+		unsigned int order = xa_get_order(xas.xa, xas.xa_index);
+		void *entry, *old = NULL;
+
+		if (order > thp_order(page))
+			xas_split_alloc(&xas, xa_load(xas.xa, xas.xa_index),
+					order, gfp);
+		xas_lock_irq(&xas);
+		xas_for_each_conflict(&xas, entry) {
+			old = entry;
+			if (!xa_is_value(entry)) {
+				xas_set_err(&xas, -EEXIST);
+				goto unlock;
+			}
+		}
+
+		if (old) {
+			if (shadowp)
+				*shadowp = old;
+			/* entry may have been split before we acquired lock */
+			order = xa_get_order(xas.xa, xas.xa_index);
+			if (order > thp_order(page)) {
+				xas_split(&xas, old, order);
+				xas_reset(&xas);
+			}
+		}
+
+		xas_store(&xas, page);
+		if (xas_error(&xas))
+			goto unlock;
+
+		if (old)
+			mapping->nrexceptional--;
+		mapping->nrpages++;
+
+		/* hugetlb pages do not participate in page cache accounting */
+		if (!huge)
+			__inc_lruvec_page_state(page, NR_FILE_PAGES);
+unlock:
+		xas_unlock_irq(&xas);
+	} while (xas_nomem(&xas, gfp));
+
+	if (xas_error(&xas)) {
+		error = xas_error(&xas);
+		if (charged)
+			mem_cgroup_uncharge(page);
+		goto error;
+	}
+
+	trace_mm_filemap_add_to_page_cache(page);
+	return 0;
+error:
+	page->mapping = NULL;
+	/* Leave page->index set: truncation relies upon it */
+	put_page(page);
+	return error;
+}
+ALLOW_ERROR_INJECTION(__add_to_page_cache_locked, ERRNO);
+
+/**
+ * add_to_page_cache_locked - add a locked page to the pagecache
+ * @page:	page to add
+ * @mapping:	the page's address_space
+ * @offset:	page index
+ * @gfp_mask:	page allocation mode
+ *
+ * This function is used to add a page to the pagecache. It must be locked.
+ * This function does not add the page to the LRU.  The caller must do that.
+ *
+ * Return: %0 on success, negative error code otherwise.
+ */
+int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
+		pgoff_t offset, gfp_t gfp_mask)
+{
+	return __add_to_page_cache_locked(page, mapping, offset,
+					  gfp_mask, NULL);
+}
+EXPORT_SYMBOL(add_to_page_cache_locked);
+
+int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
+				pgoff_t offset, gfp_t gfp_mask)
+{
+	void *shadow = NULL;
+	int ret;
+
+	__SetPageLocked(page);
+	ret = __add_to_page_cache_locked(page, mapping, offset,
+					 gfp_mask, &shadow);
+	if (unlikely(ret))
+		__ClearPageLocked(page);
+	else {
+		/*
+		 * The page might have been evicted from cache only
+		 * recently, in which case it should be activated like
+		 * any other repeatedly accessed page.
+		 * The exception is pages getting rewritten; evicting other
+		 * data from the working set, only to cache data that will
+		 * get overwritten with something else, is a waste of memory.
+		 */
+		WARN_ON_ONCE(PageActive(page));
+		if (!(gfp_mask & __GFP_WRITE) && shadow)
+			workingset_refault(page, shadow);
+		lru_cache_add(page);
+	}
+	return ret;
+}
+EXPORT_SYMBOL_GPL(add_to_page_cache_lru);
+
+#ifdef CONFIG_NUMA
+struct page *__page_cache_alloc(gfp_t gfp)
+{
+	int n;
+	struct page *page;
+
+	if (cpuset_do_page_mem_spread()) {
+		unsigned int cpuset_mems_cookie;
+		do {
+			cpuset_mems_cookie = read_mems_allowed_begin();
+			n = cpuset_mem_spread_node();
+			page = __alloc_pages_node(n, gfp, 0);
+		} while (!page && read_mems_allowed_retry(cpuset_mems_cookie));
+
+		return page;
+	}
+	return alloc_pages(gfp, 0);
+}
+EXPORT_SYMBOL(__page_cache_alloc);
+#endif
+
+/*
+ * In order to wait for pages to become available there must be
+ * waitqueues associated with pages. By using a hash table of
+ * waitqueues where the bucket discipline is to maintain all
+ * waiters on the same queue and wake all when any of the pages
+ * become available, and for the woken contexts to check to be
+ * sure the appropriate page became available, this saves space
+ * at a cost of "thundering herd" phenomena during rare hash
+ * collisions.
+ */
+#define PAGE_WAIT_TABLE_BITS 8
+#define PAGE_WAIT_TABLE_SIZE (1 << PAGE_WAIT_TABLE_BITS)
+static wait_queue_head_t page_wait_table[PAGE_WAIT_TABLE_SIZE] __cacheline_aligned;
+
+static wait_queue_head_t *page_waitqueue(struct page *page)
+{
+	return &page_wait_table[hash_ptr(page, PAGE_WAIT_TABLE_BITS)];
+}
+
+void __init pagecache_init(void)
+{
+	int i;
+
+	for (i = 0; i < PAGE_WAIT_TABLE_SIZE; i++)
+		init_waitqueue_head(&page_wait_table[i]);
+
+	page_writeback_init();
+}
+
+/*
+ * The page wait code treats the "wait->flags" somewhat unusually, because
+ * we have multiple different kinds of waits, not just the usual "exclusive"
+ * one.
+ *
+ * We have:
+ *
+ *  (a) no special bits set:
+ *
+ *	We're just waiting for the bit to be released, and when a waker
+ *	calls the wakeup function, we set WQ_FLAG_WOKEN and wake it up,
+ *	and remove it from the wait queue.
+ *
+ *	Simple and straightforward.
+ *
+ *  (b) WQ_FLAG_EXCLUSIVE:
+ *
+ *	The waiter is waiting to get the lock, and only one waiter should
+ *	be woken up to avoid any thundering herd behavior. We'll set the
+ *	WQ_FLAG_WOKEN bit, wake it up, and remove it from the wait queue.
+ *
+ *	This is the traditional exclusive wait.
+ *
+ *  (c) WQ_FLAG_EXCLUSIVE | WQ_FLAG_CUSTOM:
+ *
+ *	The waiter is waiting to get the bit, and additionally wants the
+ *	lock to be transferred to it for fair lock behavior. If the lock
+ *	cannot be taken, we stop walking the wait queue without waking
+ *	the waiter.
+ *
+ *	This is the "fair lock handoff" case, and in addition to setting
+ *	WQ_FLAG_WOKEN, we set WQ_FLAG_DONE to let the waiter easily see
+ *	that it now has the lock.
+ */
+static int wake_page_function(wait_queue_entry_t *wait, unsigned mode, int sync, void *arg)
+{
+	unsigned int flags;
+	struct wait_page_key *key = arg;
+	struct wait_page_queue *wait_page
+		= container_of(wait, struct wait_page_queue, wait);
+
+	if (!wake_page_match(wait_page, key))
+		return 0;
+
+	/*
+	 * If it's a lock handoff wait, we get the bit for it, and
+	 * stop walking (and do not wake it up) if we can't.
+	 */
+	flags = wait->flags;
+	if (flags & WQ_FLAG_EXCLUSIVE) {
+		if (test_bit(key->bit_nr, &key->page->flags))
+			return -1;
+		if (flags & WQ_FLAG_CUSTOM) {
+			if (test_and_set_bit(key->bit_nr, &key->page->flags))
+				return -1;
+			flags |= WQ_FLAG_DONE;
+		}
+	}
+
+	/*
+	 * We are holding the wait-queue lock, but the waiter that
+	 * is waiting for this will be checking the flags without
+	 * any locking.
+	 *
+	 * So update the flags atomically, and wake up the waiter
+	 * afterwards to avoid any races. This store-release pairs
+	 * with the load-acquire in wait_on_page_bit_common().
+	 */
+	smp_store_release(&wait->flags, flags | WQ_FLAG_WOKEN);
+	wake_up_state(wait->private, mode);
+
+	/*
+	 * Ok, we have successfully done what we're waiting for,
+	 * and we can unconditionally remove the wait entry.
+	 *
+	 * Note that this pairs with the "finish_wait()" in the
+	 * waiter, and has to be the absolute last thing we do.
+	 * After this list_del_init(&wait->entry) the wait entry
+	 * might be de-allocated and the process might even have
+	 * exited.
+	 */
+	list_del_init_careful(&wait->entry);
+	return (flags & WQ_FLAG_EXCLUSIVE) != 0;
+}
+
+static void wake_up_page_bit(struct page *page, int bit_nr)
+{
+	wait_queue_head_t *q = page_waitqueue(page);
+	struct wait_page_key key;
+	unsigned long flags;
+	wait_queue_entry_t bookmark;
+
+	key.page = page;
+	key.bit_nr = bit_nr;
+	key.page_match = 0;
+
+	bookmark.flags = 0;
+	bookmark.private = NULL;
+	bookmark.func = NULL;
+	INIT_LIST_HEAD(&bookmark.entry);
+
+	spin_lock_irqsave(&q->lock, flags);
+	__wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
+
+	while (bookmark.flags & WQ_FLAG_BOOKMARK) {
+		/*
+		 * Take a breather from holding the lock,
+		 * allow pages that finish wake up asynchronously
+		 * to acquire the lock and remove themselves
+		 * from wait queue
+		 */
+		spin_unlock_irqrestore(&q->lock, flags);
+		cpu_relax();
+		spin_lock_irqsave(&q->lock, flags);
+		__wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
+	}
+
+	/*
+	 * It is possible for other pages to have collided on the waitqueue
+	 * hash, so in that case check for a page match. That prevents a long-
+	 * term waiter
+	 *
+	 * It is still possible to miss a case here, when we woke page waiters
+	 * and removed them from the waitqueue, but there are still other
+	 * page waiters.
+	 */
+	if (!waitqueue_active(q) || !key.page_match) {
+		ClearPageWaiters(page);
+		/*
+		 * It's possible to miss clearing Waiters here, when we woke
+		 * our page waiters, but the hashed waitqueue has waiters for
+		 * other pages on it.
+		 *
+		 * That's okay, it's a rare case. The next waker will clear it.
+		 */
+	}
+	spin_unlock_irqrestore(&q->lock, flags);
+}
+
+static void wake_up_page(struct page *page, int bit)
+{
+	if (!PageWaiters(page))
+		return;
+	wake_up_page_bit(page, bit);
+}
+
+/*
+ * A choice of three behaviors for wait_on_page_bit_common():
+ */
+enum behavior {
+	EXCLUSIVE,	/* Hold ref to page and take the bit when woken, like
+			 * __lock_page() waiting on then setting PG_locked.
+			 */
+	SHARED,		/* Hold ref to page and check the bit when woken, like
+			 * wait_on_page_writeback() waiting on PG_writeback.
+			 */
+	DROP,		/* Drop ref to page before wait, no check when woken,
+			 * like put_and_wait_on_page_locked() on PG_locked.
+			 */
+};
+
+/*
+ * Attempt to check (or get) the page bit, and mark us done
+ * if successful.
+ */
+static inline bool trylock_page_bit_common(struct page *page, int bit_nr,
+					struct wait_queue_entry *wait)
+{
+	if (wait->flags & WQ_FLAG_EXCLUSIVE) {
+		if (test_and_set_bit(bit_nr, &page->flags))
+			return false;
+	} else if (test_bit(bit_nr, &page->flags))
+		return false;
+
+	wait->flags |= WQ_FLAG_WOKEN | WQ_FLAG_DONE;
+	return true;
+}
+
+/* How many times do we accept lock stealing from under a waiter? */
+int sysctl_page_lock_unfairness = 5;
+
+static inline int wait_on_page_bit_common(wait_queue_head_t *q,
+	struct page *page, int bit_nr, int state, enum behavior behavior)
+{
+	int unfairness = sysctl_page_lock_unfairness;
+	struct wait_page_queue wait_page;
+	wait_queue_entry_t *wait = &wait_page.wait;
+	bool thrashing = false;
+	bool delayacct = false;
+	unsigned long pflags;
+
+	if (bit_nr == PG_locked &&
+	    !PageUptodate(page) && PageWorkingset(page)) {
+		if (!PageSwapBacked(page)) {
+			delayacct_thrashing_start();
+			delayacct = true;
+		}
+		psi_memstall_enter(&pflags);
+		thrashing = true;
+	}
+
+	init_wait(wait);
+	wait->func = wake_page_function;
+	wait_page.page = page;
+	wait_page.bit_nr = bit_nr;
+
+repeat:
+	wait->flags = 0;
+	if (behavior == EXCLUSIVE) {
+		wait->flags = WQ_FLAG_EXCLUSIVE;
+		if (--unfairness < 0)
+			wait->flags |= WQ_FLAG_CUSTOM;
+	}
+
+	/*
+	 * Do one last check whether we can get the
+	 * page bit synchronously.
+	 *
+	 * Do the SetPageWaiters() marking before that
+	 * to let any waker we _just_ missed know they
+	 * need to wake us up (otherwise they'll never
+	 * even go to the slow case that looks at the
+	 * page queue), and add ourselves to the wait
+	 * queue if we need to sleep.
+	 *
+	 * This part needs to be done under the queue
+	 * lock to avoid races.
+	 */
+	spin_lock_irq(&q->lock);
+	SetPageWaiters(page);
+	if (!trylock_page_bit_common(page, bit_nr, wait))
+		__add_wait_queue_entry_tail(q, wait);
+	spin_unlock_irq(&q->lock);
+
+	/*
+	 * From now on, all the logic will be based on
+	 * the WQ_FLAG_WOKEN and WQ_FLAG_DONE flag, to
+	 * see whether the page bit testing has already
+	 * been done by the wake function.
+	 *
+	 * We can drop our reference to the page.
+	 */
+	if (behavior == DROP)
+		put_page(page);
+
+	/*
+	 * Note that until the "finish_wait()", or until
+	 * we see the WQ_FLAG_WOKEN flag, we need to
+	 * be very careful with the 'wait->flags', because
+	 * we may race with a waker that sets them.
+	 */
+	for (;;) {
+		unsigned int flags;
+
+		set_current_state(state);
+
+		/* Loop until we've been woken or interrupted */
+		flags = smp_load_acquire(&wait->flags);
+		if (!(flags & WQ_FLAG_WOKEN)) {
+			if (signal_pending_state(state, current))
+				break;
+
+			io_schedule();
+			continue;
+		}
+
+		/* If we were non-exclusive, we're done */
+		if (behavior != EXCLUSIVE)
+			break;
+
+		/* If the waker got the lock for us, we're done */
+		if (flags & WQ_FLAG_DONE)
+			break;
+
+		/*
+		 * Otherwise, if we're getting the lock, we need to
+		 * try to get it ourselves.
+		 *
+		 * And if that fails, we'll have to retry this all.
+		 */
+		if (unlikely(test_and_set_bit(bit_nr, &page->flags)))
+			goto repeat;
+
+		wait->flags |= WQ_FLAG_DONE;
+		break;
+	}
+
+	/*
+	 * If a signal happened, this 'finish_wait()' may remove the last
+	 * waiter from the wait-queues, but the PageWaiters bit will remain
+	 * set. That's ok. The next wakeup will take care of it, and trying
+	 * to do it here would be difficult and prone to races.
+	 */
+	finish_wait(q, wait);
+
+	if (thrashing) {
+		if (delayacct)
+			delayacct_thrashing_end();
+		psi_memstall_leave(&pflags);
+	}
+
+	/*
+	 * NOTE! The wait->flags weren't stable until we've done the
+	 * 'finish_wait()', and we could have exited the loop above due
+	 * to a signal, and had a wakeup event happen after the signal
+	 * test but before the 'finish_wait()'.
+	 *
+	 * So only after the finish_wait() can we reliably determine
+	 * if we got woken up or not, so we can now figure out the final
+	 * return value based on that state without races.
+	 *
+	 * Also note that WQ_FLAG_WOKEN is sufficient for a non-exclusive
+	 * waiter, but an exclusive one requires WQ_FLAG_DONE.
+	 */
+	if (behavior == EXCLUSIVE)
+		return wait->flags & WQ_FLAG_DONE ? 0 : -EINTR;
+
+	return wait->flags & WQ_FLAG_WOKEN ? 0 : -EINTR;
+}
+
+void wait_on_page_bit(struct page *page, int bit_nr)
+{
+	wait_queue_head_t *q = page_waitqueue(page);
+	wait_on_page_bit_common(q, page, bit_nr, TASK_UNINTERRUPTIBLE, SHARED);
+}
+EXPORT_SYMBOL(wait_on_page_bit);
+
+int wait_on_page_bit_killable(struct page *page, int bit_nr)
+{
+	wait_queue_head_t *q = page_waitqueue(page);
+	return wait_on_page_bit_common(q, page, bit_nr, TASK_KILLABLE, SHARED);
+}
+EXPORT_SYMBOL(wait_on_page_bit_killable);
+
+static int __wait_on_page_locked_async(struct page *page,
+				       struct wait_page_queue *wait, bool set)
+{
+	struct wait_queue_head *q = page_waitqueue(page);
+	int ret = 0;
+
+	wait->page = page;
+	wait->bit_nr = PG_locked;
+
+	spin_lock_irq(&q->lock);
+	__add_wait_queue_entry_tail(q, &wait->wait);
+	SetPageWaiters(page);
+	if (set)
+		ret = !trylock_page(page);
+	else
+		ret = PageLocked(page);
+	/*
+	 * If we were succesful now, we know we're still on the
+	 * waitqueue as we're still under the lock. This means it's
+	 * safe to remove and return success, we know the callback
+	 * isn't going to trigger.
+	 */
+	if (!ret)
+		__remove_wait_queue(q, &wait->wait);
+	else
+		ret = -EIOCBQUEUED;
+	spin_unlock_irq(&q->lock);
+	return ret;
+}
+
+static int wait_on_page_locked_async(struct page *page,
+				     struct wait_page_queue *wait)
+{
+	if (!PageLocked(page))
+		return 0;
+	return __wait_on_page_locked_async(compound_head(page), wait, false);
+}
+
+/**
+ * put_and_wait_on_page_locked - Drop a reference and wait for it to be unlocked
+ * @page: The page to wait for.
+ *
+ * The caller should hold a reference on @page.  They expect the page to
+ * become unlocked relatively soon, but do not wish to hold up migration
+ * (for example) by holding the reference while waiting for the page to
+ * come unlocked.  After this function returns, the caller should not
+ * dereference @page.
+ */
+void put_and_wait_on_page_locked(struct page *page)
+{
+	wait_queue_head_t *q;
+
+	page = compound_head(page);
+	q = page_waitqueue(page);
+	wait_on_page_bit_common(q, page, PG_locked, TASK_UNINTERRUPTIBLE, DROP);
+}
+
+/**
+ * add_page_wait_queue - Add an arbitrary waiter to a page's wait queue
+ * @page: Page defining the wait queue of interest
+ * @waiter: Waiter to add to the queue
+ *
+ * Add an arbitrary @waiter to the wait queue for the nominated @page.
+ */
+void add_page_wait_queue(struct page *page, wait_queue_entry_t *waiter)
+{
+	wait_queue_head_t *q = page_waitqueue(page);
+	unsigned long flags;
+
+	spin_lock_irqsave(&q->lock, flags);
+	__add_wait_queue_entry_tail(q, waiter);
+	SetPageWaiters(page);
+	spin_unlock_irqrestore(&q->lock, flags);
+}
+EXPORT_SYMBOL_GPL(add_page_wait_queue);
+
+#ifndef clear_bit_unlock_is_negative_byte
+
+/*
+ * PG_waiters is the high bit in the same byte as PG_lock.
+ *
+ * On x86 (and on many other architectures), we can clear PG_lock and
+ * test the sign bit at the same time. But if the architecture does
+ * not support that special operation, we just do this all by hand
+ * instead.
+ *
+ * The read of PG_waiters has to be after (or concurrently with) PG_locked
+ * being cleared, but a memory barrier should be unnecessary since it is
+ * in the same byte as PG_locked.
+ */
+static inline bool clear_bit_unlock_is_negative_byte(long nr, volatile void *mem)
+{
+	clear_bit_unlock(nr, mem);
+	/* smp_mb__after_atomic(); */
+	return test_bit(PG_waiters, mem);
+}
+
+#endif
+
+/**
+ * unlock_page - unlock a locked page
+ * @page: the page
+ *
+ * Unlocks the page and wakes up sleepers in wait_on_page_locked().
+ * Also wakes sleepers in wait_on_page_writeback() because the wakeup
+ * mechanism between PageLocked pages and PageWriteback pages is shared.
+ * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
+ *
+ * Note that this depends on PG_waiters being the sign bit in the byte
+ * that contains PG_locked - thus the BUILD_BUG_ON(). That allows us to
+ * clear the PG_locked bit and test PG_waiters at the same time fairly
+ * portably (architectures that do LL/SC can test any bit, while x86 can
+ * test the sign bit).
+ */
+void unlock_page(struct page *page)
+{
+	BUILD_BUG_ON(PG_waiters != 7);
+	page = compound_head(page);
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	if (clear_bit_unlock_is_negative_byte(PG_locked, &page->flags))
+		wake_up_page_bit(page, PG_locked);
+}
+EXPORT_SYMBOL(unlock_page);
+
+/**
+ * end_page_writeback - end writeback against a page
+ * @page: the page
+ */
+void end_page_writeback(struct page *page)
+{
+	/*
+	 * TestClearPageReclaim could be used here but it is an atomic
+	 * operation and overkill in this particular case. Failing to
+	 * shuffle a page marked for immediate reclaim is too mild to
+	 * justify taking an atomic operation penalty at the end of
+	 * ever page writeback.
+	 */
+	if (PageReclaim(page)) {
+		ClearPageReclaim(page);
+		rotate_reclaimable_page(page);
+	}
+
+	/*
+	 * Writeback does not hold a page reference of its own, relying
+	 * on truncation to wait for the clearing of PG_writeback.
+	 * But here we must make sure that the page is not freed and
+	 * reused before the wake_up_page().
+	 */
+	get_page(page);
+	if (!test_clear_page_writeback(page))
+		BUG();
+
+	smp_mb__after_atomic();
+	wake_up_page(page, PG_writeback);
+	put_page(page);
+}
+EXPORT_SYMBOL(end_page_writeback);
+
+/*
+ * After completing I/O on a page, call this routine to update the page
+ * flags appropriately
+ */
+void page_endio(struct page *page, bool is_write, int err)
+{
+	if (!is_write) {
+		if (!err) {
+			SetPageUptodate(page);
+		} else {
+			ClearPageUptodate(page);
+			SetPageError(page);
+		}
+		unlock_page(page);
+	} else {
+		if (err) {
+			struct address_space *mapping;
+
+			SetPageError(page);
+			mapping = page_mapping(page);
+			if (mapping)
+				mapping_set_error(mapping, err);
+		}
+		end_page_writeback(page);
+	}
+}
+EXPORT_SYMBOL_GPL(page_endio);
+
+/**
+ * __lock_page - get a lock on the page, assuming we need to sleep to get it
+ * @__page: the page to lock
+ */
+void __lock_page(struct page *__page)
+{
+	struct page *page = compound_head(__page);
+	wait_queue_head_t *q = page_waitqueue(page);
+	wait_on_page_bit_common(q, page, PG_locked, TASK_UNINTERRUPTIBLE,
+				EXCLUSIVE);
+}
+EXPORT_SYMBOL(__lock_page);
+
+int __lock_page_killable(struct page *__page)
+{
+	struct page *page = compound_head(__page);
+	wait_queue_head_t *q = page_waitqueue(page);
+	return wait_on_page_bit_common(q, page, PG_locked, TASK_KILLABLE,
+					EXCLUSIVE);
+}
+EXPORT_SYMBOL_GPL(__lock_page_killable);
+
+int __lock_page_async(struct page *page, struct wait_page_queue *wait)
+{
+	return __wait_on_page_locked_async(page, wait, true);
+}
+
+/*
+ * Return values:
+ * 1 - page is locked; mmap_lock is still held.
+ * 0 - page is not locked.
+ *     mmap_lock has been released (mmap_read_unlock(), unless flags had both
+ *     FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT set, in
+ *     which case mmap_lock is still held.
+ *
+ * If neither ALLOW_RETRY nor KILLABLE are set, will always return 1
+ * with the page locked and the mmap_lock unperturbed.
+ */
+int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
+			 unsigned int flags)
+{
+	if (fault_flag_allow_retry_first(flags)) {
+		/*
+		 * CAUTION! In this case, mmap_lock is not released
+		 * even though return 0.
+		 */
+		if (flags & FAULT_FLAG_RETRY_NOWAIT)
+			return 0;
+
+		mmap_read_unlock(mm);
+		if (flags & FAULT_FLAG_KILLABLE)
+			wait_on_page_locked_killable(page);
+		else
+			wait_on_page_locked(page);
+		return 0;
+	} else {
+		if (flags & FAULT_FLAG_KILLABLE) {
+			int ret;
+
+			ret = __lock_page_killable(page);
+			if (ret) {
+				mmap_read_unlock(mm);
+				return 0;
+			}
+		} else
+			__lock_page(page);
+		return 1;
+	}
+}
+
+/**
+ * page_cache_next_miss() - Find the next gap in the page cache.
+ * @mapping: Mapping.
+ * @index: Index.
+ * @max_scan: Maximum range to search.
+ *
+ * Search the range [index, min(index + max_scan - 1, ULONG_MAX)] for the
+ * gap with the lowest index.
+ *
+ * This function may be called under the rcu_read_lock.  However, this will
+ * not atomically search a snapshot of the cache at a single point in time.
+ * For example, if a gap is created at index 5, then subsequently a gap is
+ * created at index 10, page_cache_next_miss covering both indices may
+ * return 10 if called under the rcu_read_lock.
+ *
+ * Return: The index of the gap if found, otherwise an index outside the
+ * range specified (in which case 'return - index >= max_scan' will be true).
+ * In the rare case of index wrap-around, 0 will be returned.
+ */
+pgoff_t page_cache_next_miss(struct address_space *mapping,
+			     pgoff_t index, unsigned long max_scan)
+{
+	XA_STATE(xas, &mapping->i_pages, index);
+
+	while (max_scan--) {
+		void *entry = xas_next(&xas);
+		if (!entry || xa_is_value(entry))
+			break;
+		if (xas.xa_index == 0)
+			break;
+	}
+
+	return xas.xa_index;
+}
+EXPORT_SYMBOL(page_cache_next_miss);
+
+/**
+ * page_cache_prev_miss() - Find the previous gap in the page cache.
+ * @mapping: Mapping.
+ * @index: Index.
+ * @max_scan: Maximum range to search.
+ *
+ * Search the range [max(index - max_scan + 1, 0), index] for the
+ * gap with the highest index.
+ *
+ * This function may be called under the rcu_read_lock.  However, this will
+ * not atomically search a snapshot of the cache at a single point in time.
+ * For example, if a gap is created at index 10, then subsequently a gap is
+ * created at index 5, page_cache_prev_miss() covering both indices may
+ * return 5 if called under the rcu_read_lock.
+ *
+ * Return: The index of the gap if found, otherwise an index outside the
+ * range specified (in which case 'index - return >= max_scan' will be true).
+ * In the rare case of wrap-around, ULONG_MAX will be returned.
+ */
+pgoff_t page_cache_prev_miss(struct address_space *mapping,
+			     pgoff_t index, unsigned long max_scan)
+{
+	XA_STATE(xas, &mapping->i_pages, index);
+
+	while (max_scan--) {
+		void *entry = xas_prev(&xas);
+		if (!entry || xa_is_value(entry))
+			break;
+		if (xas.xa_index == ULONG_MAX)
+			break;
+	}
+
+	return xas.xa_index;
+}
+EXPORT_SYMBOL(page_cache_prev_miss);
+
+/**
+ * find_get_entry - find and get a page cache entry
+ * @mapping: the address_space to search
+ * @index: The page cache index.
+ *
+ * Looks up the page cache slot at @mapping & @offset.  If there is a
+ * page cache page, the head page is returned with an increased refcount.
+ *
+ * If the slot holds a shadow entry of a previously evicted page, or a
+ * swap entry from shmem/tmpfs, it is returned.
+ *
+ * Return: The head page or shadow entry, %NULL if nothing is found.
+ */
+struct page *find_get_entry(struct address_space *mapping, pgoff_t index)
+{
+	XA_STATE(xas, &mapping->i_pages, index);
+	struct page *page;
+
+	rcu_read_lock();
+repeat:
+	xas_reset(&xas);
+	page = xas_load(&xas);
+	if (xas_retry(&xas, page))
+		goto repeat;
+	/*
+	 * A shadow entry of a recently evicted page, or a swap entry from
+	 * shmem/tmpfs.  Return it without attempting to raise page count.
+	 */
+	if (!page || xa_is_value(page))
+		goto out;
+
+	if (!page_cache_get_speculative(page))
+		goto repeat;
+
+	/*
+	 * Has the page moved or been split?
+	 * This is part of the lockless pagecache protocol. See
+	 * include/linux/pagemap.h for details.
+	 */
+	if (unlikely(page != xas_reload(&xas))) {
+		put_page(page);
+		goto repeat;
+	}
+out:
+	rcu_read_unlock();
+
+	return page;
+}
+
+/**
+ * find_lock_entry - Locate and lock a page cache entry.
+ * @mapping: The address_space to search.
+ * @index: The page cache index.
+ *
+ * Looks up the page at @mapping & @index.  If there is a page in the
+ * cache, the head page is returned locked and with an increased refcount.
+ *
+ * If the slot holds a shadow entry of a previously evicted page, or a
+ * swap entry from shmem/tmpfs, it is returned.
+ *
+ * Context: May sleep.
+ * Return: The head page or shadow entry, %NULL if nothing is found.
+ */
+struct page *find_lock_entry(struct address_space *mapping, pgoff_t index)
+{
+	struct page *page;
+
+repeat:
+	page = find_get_entry(mapping, index);
+	if (page && !xa_is_value(page)) {
+		lock_page(page);
+		/* Has the page been truncated? */
+		if (unlikely(page->mapping != mapping)) {
+			unlock_page(page);
+			put_page(page);
+			goto repeat;
+		}
+		VM_BUG_ON_PAGE(!thp_contains(page, index), page);
+	}
+	return page;
+}
+
+/**
+ * pagecache_get_page - Find and get a reference to a page.
+ * @mapping: The address_space to search.
+ * @index: The page index.
+ * @fgp_flags: %FGP flags modify how the page is returned.
+ * @gfp_mask: Memory allocation flags to use if %FGP_CREAT is specified.
+ *
+ * Looks up the page cache entry at @mapping & @index.
+ *
+ * @fgp_flags can be zero or more of these flags:
+ *
+ * * %FGP_ACCESSED - The page will be marked accessed.
+ * * %FGP_LOCK - The page is returned locked.
+ * * %FGP_HEAD - If the page is present and a THP, return the head page
+ *   rather than the exact page specified by the index.
+ * * %FGP_CREAT - If no page is present then a new page is allocated using
+ *   @gfp_mask and added to the page cache and the VM's LRU list.
+ *   The page is returned locked and with an increased refcount.
+ * * %FGP_FOR_MMAP - The caller wants to do its own locking dance if the
+ *   page is already in cache.  If the page was allocated, unlock it before
+ *   returning so the caller can do the same dance.
+ * * %FGP_WRITE - The page will be written
+ * * %FGP_NOFS - __GFP_FS will get cleared in gfp mask
+ * * %FGP_NOWAIT - Don't get blocked by page lock
+ *
+ * If %FGP_LOCK or %FGP_CREAT are specified then the function may sleep even
+ * if the %GFP flags specified for %FGP_CREAT are atomic.
+ *
+ * If there is a page cache page, it is returned with an increased refcount.
+ *
+ * Return: The found page or %NULL otherwise.
+ */
+struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
+		int fgp_flags, gfp_t gfp_mask)
+{
+	struct page *page;
+
+repeat:
+	page = find_get_entry(mapping, index);
+	if (xa_is_value(page))
+		page = NULL;
+	if (!page)
+		goto no_page;
+
+	if (fgp_flags & FGP_LOCK) {
+		if (fgp_flags & FGP_NOWAIT) {
+			if (!trylock_page(page)) {
+				put_page(page);
+				return NULL;
+			}
+		} else {
+			lock_page(page);
+		}
+
+		/* Has the page been truncated? */
+		if (unlikely(page->mapping != mapping)) {
+			unlock_page(page);
+			put_page(page);
+			goto repeat;
+		}
+		VM_BUG_ON_PAGE(!thp_contains(page, index), page);
+	}
+
+	if (fgp_flags & FGP_ACCESSED)
+		mark_page_accessed(page);
+	else if (fgp_flags & FGP_WRITE) {
+		/* Clear idle flag for buffer write */
+		if (page_is_idle(page))
+			clear_page_idle(page);
+	}
+	if (!(fgp_flags & FGP_HEAD))
+		page = find_subpage(page, index);
+
+no_page:
+	if (!page && (fgp_flags & FGP_CREAT)) {
+		int err;
+		if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
+			gfp_mask |= __GFP_WRITE;
+		if (fgp_flags & FGP_NOFS)
+			gfp_mask &= ~__GFP_FS;
+
+		page = __page_cache_alloc(gfp_mask);
+		if (!page)
+			return NULL;
+
+		if (WARN_ON_ONCE(!(fgp_flags & (FGP_LOCK | FGP_FOR_MMAP))))
+			fgp_flags |= FGP_LOCK;
+
+		/* Init accessed so avoid atomic mark_page_accessed later */
+		if (fgp_flags & FGP_ACCESSED)
+			__SetPageReferenced(page);
+
+		err = add_to_page_cache_lru(page, mapping, index, gfp_mask);
+		if (unlikely(err)) {
+			put_page(page);
+			page = NULL;
+			if (err == -EEXIST)
+				goto repeat;
+		}
+
+		/*
+		 * add_to_page_cache_lru locks the page, and for mmap we expect
+		 * an unlocked page.
+		 */
+		if (page && (fgp_flags & FGP_FOR_MMAP))
+			unlock_page(page);
+	}
+
+	return page;
+}
+EXPORT_SYMBOL(pagecache_get_page);
+
+/**
+ * find_get_entries - gang pagecache lookup
+ * @mapping:	The address_space to search
+ * @start:	The starting page cache index
+ * @nr_entries:	The maximum number of entries
+ * @entries:	Where the resulting entries are placed
+ * @indices:	The cache indices corresponding to the entries in @entries
+ *
+ * find_get_entries() will search for and return a group of up to
+ * @nr_entries entries in the mapping.  The entries are placed at
+ * @entries.  find_get_entries() takes a reference against any actual
+ * pages it returns.
+ *
+ * The search returns a group of mapping-contiguous page cache entries
+ * with ascending indexes.  There may be holes in the indices due to
+ * not-present pages.
+ *
+ * Any shadow entries of evicted pages, or swap entries from
+ * shmem/tmpfs, are included in the returned array.
+ *
+ * If it finds a Transparent Huge Page, head or tail, find_get_entries()
+ * stops at that page: the caller is likely to have a better way to handle
+ * the compound page as a whole, and then skip its extent, than repeatedly
+ * calling find_get_entries() to return all its tails.
+ *
+ * Return: the number of pages and shadow entries which were found.
+ */
+unsigned find_get_entries(struct address_space *mapping,
+			  pgoff_t start, unsigned int nr_entries,
+			  struct page **entries, pgoff_t *indices)
+{
+	XA_STATE(xas, &mapping->i_pages, start);
+	struct page *page;
+	unsigned int ret = 0;
+
+	if (!nr_entries)
+		return 0;
+
+	rcu_read_lock();
+	xas_for_each(&xas, page, ULONG_MAX) {
+		if (xas_retry(&xas, page))
+			continue;
+		/*
+		 * A shadow entry of a recently evicted page, a swap
+		 * entry from shmem/tmpfs or a DAX entry.  Return it
+		 * without attempting to raise page count.
+		 */
+		if (xa_is_value(page))
+			goto export;
+
+		if (!page_cache_get_speculative(page))
+			goto retry;
+
+		/* Has the page moved or been split? */
+		if (unlikely(page != xas_reload(&xas)))
+			goto put_page;
+
+		/*
+		 * Terminate early on finding a THP, to allow the caller to
+		 * handle it all at once; but continue if this is hugetlbfs.
+		 */
+		if (PageTransHuge(page) && !PageHuge(page)) {
+			page = find_subpage(page, xas.xa_index);
+			nr_entries = ret + 1;
+		}
+export:
+		indices[ret] = xas.xa_index;
+		entries[ret] = page;
+		if (++ret == nr_entries)
+			break;
+		continue;
+put_page:
+		put_page(page);
+retry:
+		xas_reset(&xas);
+	}
+	rcu_read_unlock();
+	return ret;
+}
+
+/**
+ * find_get_pages_range - gang pagecache lookup
+ * @mapping:	The address_space to search
+ * @start:	The starting page index
+ * @end:	The final page index (inclusive)
+ * @nr_pages:	The maximum number of pages
+ * @pages:	Where the resulting pages are placed
+ *
+ * find_get_pages_range() will search for and return a group of up to @nr_pages
+ * pages in the mapping starting at index @start and up to index @end
+ * (inclusive).  The pages are placed at @pages.  find_get_pages_range() takes
+ * a reference against the returned pages.
+ *
+ * The search returns a group of mapping-contiguous pages with ascending
+ * indexes.  There may be holes in the indices due to not-present pages.
+ * We also update @start to index the next page for the traversal.
+ *
+ * Return: the number of pages which were found. If this number is
+ * smaller than @nr_pages, the end of specified range has been
+ * reached.
+ */
+unsigned find_get_pages_range(struct address_space *mapping, pgoff_t *start,
+			      pgoff_t end, unsigned int nr_pages,
+			      struct page **pages)
+{
+	XA_STATE(xas, &mapping->i_pages, *start);
+	struct page *page;
+	unsigned ret = 0;
+
+	if (unlikely(!nr_pages))
+		return 0;
+
+	rcu_read_lock();
+	xas_for_each(&xas, page, end) {
+		if (xas_retry(&xas, page))
+			continue;
+		/* Skip over shadow, swap and DAX entries */
+		if (xa_is_value(page))
+			continue;
+
+		if (!page_cache_get_speculative(page))
+			goto retry;
+
+		/* Has the page moved or been split? */
+		if (unlikely(page != xas_reload(&xas)))
+			goto put_page;
+
+		pages[ret] = find_subpage(page, xas.xa_index);
+		if (++ret == nr_pages) {
+			*start = xas.xa_index + 1;
+			goto out;
+		}
+		continue;
+put_page:
+		put_page(page);
+retry:
+		xas_reset(&xas);
+	}
+
+	/*
+	 * We come here when there is no page beyond @end. We take care to not
+	 * overflow the index @start as it confuses some of the callers. This
+	 * breaks the iteration when there is a page at index -1 but that is
+	 * already broken anyway.
+	 */
+	if (end == (pgoff_t)-1)
+		*start = (pgoff_t)-1;
+	else
+		*start = end + 1;
+out:
+	rcu_read_unlock();
+
+	return ret;
+}
+
+/**
+ * find_get_pages_contig - gang contiguous pagecache lookup
+ * @mapping:	The address_space to search
+ * @index:	The starting page index
+ * @nr_pages:	The maximum number of pages
+ * @pages:	Where the resulting pages are placed
+ *
+ * find_get_pages_contig() works exactly like find_get_pages(), except
+ * that the returned number of pages are guaranteed to be contiguous.
+ *
+ * Return: the number of pages which were found.
+ */
+unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
+			       unsigned int nr_pages, struct page **pages)
+{
+	XA_STATE(xas, &mapping->i_pages, index);
+	struct page *page;
+	unsigned int ret = 0;
+
+	if (unlikely(!nr_pages))
+		return 0;
+
+	rcu_read_lock();
+	for (page = xas_load(&xas); page; page = xas_next(&xas)) {
+		if (xas_retry(&xas, page))
+			continue;
+		/*
+		 * If the entry has been swapped out, we can stop looking.
+		 * No current caller is looking for DAX entries.
+		 */
+		if (xa_is_value(page))
+			break;
+
+		if (!page_cache_get_speculative(page))
+			goto retry;
+
+		/* Has the page moved or been split? */
+		if (unlikely(page != xas_reload(&xas)))
+			goto put_page;
+
+		pages[ret] = find_subpage(page, xas.xa_index);
+		if (++ret == nr_pages)
+			break;
+		continue;
+put_page:
+		put_page(page);
+retry:
+		xas_reset(&xas);
+	}
+	rcu_read_unlock();
+	return ret;
+}
+EXPORT_SYMBOL(find_get_pages_contig);
+
+/**
+ * find_get_pages_range_tag - find and return pages in given range matching @tag
+ * @mapping:	the address_space to search
+ * @index:	the starting page index
+ * @end:	The final page index (inclusive)
+ * @tag:	the tag index
+ * @nr_pages:	the maximum number of pages
+ * @pages:	where the resulting pages are placed
+ *
+ * Like find_get_pages, except we only return pages which are tagged with
+ * @tag.   We update @index to index the next page for the traversal.
+ *
+ * Return: the number of pages which were found.
+ */
+unsigned find_get_pages_range_tag(struct address_space *mapping, pgoff_t *index,
+			pgoff_t end, xa_mark_t tag, unsigned int nr_pages,
+			struct page **pages)
+{
+	XA_STATE(xas, &mapping->i_pages, *index);
+	struct page *page;
+	unsigned ret = 0;
+
+	if (unlikely(!nr_pages))
+		return 0;
+
+	rcu_read_lock();
+	xas_for_each_marked(&xas, page, end, tag) {
+		if (xas_retry(&xas, page))
+			continue;
+		/*
+		 * Shadow entries should never be tagged, but this iteration
+		 * is lockless so there is a window for page reclaim to evict
+		 * a page we saw tagged.  Skip over it.
+		 */
+		if (xa_is_value(page))
+			continue;
+
+		if (!page_cache_get_speculative(page))
+			goto retry;
+
+		/* Has the page moved or been split? */
+		if (unlikely(page != xas_reload(&xas)))
+			goto put_page;
+
+		pages[ret] = find_subpage(page, xas.xa_index);
+		if (++ret == nr_pages) {
+			*index = xas.xa_index + 1;
+			goto out;
+		}
+		continue;
+put_page:
+		put_page(page);
+retry:
+		xas_reset(&xas);
+	}
+
+	/*
+	 * We come here when we got to @end. We take care to not overflow the
+	 * index @index as it confuses some of the callers. This breaks the
+	 * iteration when there is a page at index -1 but that is already
+	 * broken anyway.
+	 */
+	if (end == (pgoff_t)-1)
+		*index = (pgoff_t)-1;
+	else
+		*index = end + 1;
+out:
+	rcu_read_unlock();
+
+	return ret;
+}
+EXPORT_SYMBOL(find_get_pages_range_tag);
+
+/*
+ * CD/DVDs are error prone. When a medium error occurs, the driver may fail
+ * a _large_ part of the i/o request. Imagine the worst scenario:
+ *
+ *      ---R__________________________________________B__________
+ *         ^ reading here                             ^ bad block(assume 4k)
+ *
+ * read(R) => miss => readahead(R...B) => media error => frustrating retries
+ * => failing the whole request => read(R) => read(R+1) =>
+ * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
+ * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
+ * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
+ *
+ * It is going insane. Fix it by quickly scaling down the readahead size.
+ */
+static void shrink_readahead_size_eio(struct file_ra_state *ra)
+{
+	ra->ra_pages /= 4;
+}
+
+/**
+ * generic_file_buffered_read - generic file read routine
+ * @iocb:	the iocb to read
+ * @iter:	data destination
+ * @written:	already copied
+ *
+ * This is a generic file read routine, and uses the
+ * mapping->a_ops->readpage() function for the actual low-level stuff.
+ *
+ * This is really ugly. But the goto's actually try to clarify some
+ * of the logic when it comes to error handling etc.
+ *
+ * Return:
+ * * total number of bytes copied, including those the were already @written
+ * * negative error code if nothing was copied
+ */
+ssize_t generic_file_buffered_read(struct kiocb *iocb,
+		struct iov_iter *iter, ssize_t written)
+{
+	struct file *filp = iocb->ki_filp;
+	struct address_space *mapping = filp->f_mapping;
+	struct inode *inode = mapping->host;
+	struct file_ra_state *ra = &filp->f_ra;
+	loff_t *ppos = &iocb->ki_pos;
+	pgoff_t index;
+	pgoff_t last_index;
+	pgoff_t prev_index;
+	unsigned long offset;      /* offset into pagecache page */
+	unsigned int prev_offset;
+	int error = 0;
+
+	if (unlikely(*ppos >= inode->i_sb->s_maxbytes))
+		return 0;
+	if (unlikely(!iov_iter_count(iter)))
+		return 0;
+
+	iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
+
+	index = *ppos >> PAGE_SHIFT;
+	prev_index = ra->prev_pos >> PAGE_SHIFT;
+	prev_offset = ra->prev_pos & (PAGE_SIZE-1);
+	last_index = (*ppos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT;
+	offset = *ppos & ~PAGE_MASK;
+
+	/*
+	 * If we've already successfully copied some data, then we
+	 * can no longer safely return -EIOCBQUEUED. Hence mark
+	 * an async read NOWAIT at that point.
+	 */
+	if (written && (iocb->ki_flags & IOCB_WAITQ))
+		iocb->ki_flags |= IOCB_NOWAIT;
+
+	for (;;) {
+		struct page *page;
+		pgoff_t end_index;
+		loff_t isize;
+		unsigned long nr, ret;
+
+		cond_resched();
+find_page:
+		if (fatal_signal_pending(current)) {
+			error = -EINTR;
+			goto out;
+		}
+
+		page = find_get_page(mapping, index);
+		if (!page) {
+			if (iocb->ki_flags & IOCB_NOIO)
+				goto would_block;
+			page_cache_sync_readahead(mapping,
+					ra, filp,
+					index, last_index - index);
+			page = find_get_page(mapping, index);
+			if (unlikely(page == NULL))
+				goto no_cached_page;
+		}
+		if (PageReadahead(page)) {
+			if (iocb->ki_flags & IOCB_NOIO) {
+				put_page(page);
+				goto out;
+			}
+			page_cache_async_readahead(mapping,
+					ra, filp, page,
+					index, last_index - index);
+		}
+		if (!PageUptodate(page)) {
+			/*
+			 * See comment in do_read_cache_page on why
+			 * wait_on_page_locked is used to avoid unnecessarily
+			 * serialisations and why it's safe.
+			 */
+			if (iocb->ki_flags & IOCB_WAITQ) {
+				if (written) {
+					put_page(page);
+					goto out;
+				}
+				error = wait_on_page_locked_async(page,
+								iocb->ki_waitq);
+			} else {
+				if (iocb->ki_flags & IOCB_NOWAIT) {
+					put_page(page);
+					goto would_block;
+				}
+				error = wait_on_page_locked_killable(page);
+			}
+			if (unlikely(error))
+				goto readpage_error;
+			if (PageUptodate(page))
+				goto page_ok;
+
+			if (inode->i_blkbits == PAGE_SHIFT ||
+					!mapping->a_ops->is_partially_uptodate)
+				goto page_not_up_to_date;
+			/* pipes can't handle partially uptodate pages */
+			if (unlikely(iov_iter_is_pipe(iter)))
+				goto page_not_up_to_date;
+			if (!trylock_page(page))
+				goto page_not_up_to_date;
+			/* Did it get truncated before we got the lock? */
+			if (!page->mapping)
+				goto page_not_up_to_date_locked;
+			if (!mapping->a_ops->is_partially_uptodate(page,
+							offset, iter->count))
+				goto page_not_up_to_date_locked;
+			unlock_page(page);
+		}
+page_ok:
+		/*
+		 * i_size must be checked after we know the page is Uptodate.
+		 *
+		 * Checking i_size after the check allows us to calculate
+		 * the correct value for "nr", which means the zero-filled
+		 * part of the page is not copied back to userspace (unless
+		 * another truncate extends the file - this is desired though).
+		 */
+
+		isize = i_size_read(inode);
+		end_index = (isize - 1) >> PAGE_SHIFT;
+		if (unlikely(!isize || index > end_index)) {
+			put_page(page);
+			goto out;
+		}
+
+		/* nr is the maximum number of bytes to copy from this page */
+		nr = PAGE_SIZE;
+		if (index == end_index) {
+			nr = ((isize - 1) & ~PAGE_MASK) + 1;
+			if (nr <= offset) {
+				put_page(page);
+				goto out;
+			}
+		}
+		nr = nr - offset;
+
+		/* If users can be writing to this page using arbitrary
+		 * virtual addresses, take care about potential aliasing
+		 * before reading the page on the kernel side.
+		 */
+		if (mapping_writably_mapped(mapping))
+			flush_dcache_page(page);
+
+		/*
+		 * When a sequential read accesses a page several times,
+		 * only mark it as accessed the first time.
+		 */
+		if (prev_index != index || offset != prev_offset)
+			mark_page_accessed(page);
+		prev_index = index;
+
+		/*
+		 * Ok, we have the page, and it's up-to-date, so
+		 * now we can copy it to user space...
+		 */
+
+		ret = copy_page_to_iter(page, offset, nr, iter);
+		offset += ret;
+		index += offset >> PAGE_SHIFT;
+		offset &= ~PAGE_MASK;
+		prev_offset = offset;
+
+		put_page(page);
+		written += ret;
+		if (!iov_iter_count(iter))
+			goto out;
+		if (ret < nr) {
+			error = -EFAULT;
+			goto out;
+		}
+		continue;
+
+page_not_up_to_date:
+		/* Get exclusive access to the page ... */
+		if (iocb->ki_flags & IOCB_WAITQ) {
+			if (written) {
+				put_page(page);
+				goto out;
+			}
+			error = lock_page_async(page, iocb->ki_waitq);
+		} else {
+			error = lock_page_killable(page);
+		}
+		if (unlikely(error))
+			goto readpage_error;
+
+page_not_up_to_date_locked:
+		/* Did it get truncated before we got the lock? */
+		if (!page->mapping) {
+			unlock_page(page);
+			put_page(page);
+			continue;
+		}
+
+		/* Did somebody else fill it already? */
+		if (PageUptodate(page)) {
+			unlock_page(page);
+			goto page_ok;
+		}
+
+readpage:
+		if (iocb->ki_flags & (IOCB_NOIO | IOCB_NOWAIT)) {
+			unlock_page(page);
+			put_page(page);
+			goto would_block;
+		}
+		/*
+		 * A previous I/O error may have been due to temporary
+		 * failures, eg. multipath errors.
+		 * PG_error will be set again if readpage fails.
+		 */
+		ClearPageError(page);
+		/* Start the actual read. The read will unlock the page. */
+		error = mapping->a_ops->readpage(filp, page);
+
+		if (unlikely(error)) {
+			if (error == AOP_TRUNCATED_PAGE) {
+				put_page(page);
+				error = 0;
+				goto find_page;
+			}
+			goto readpage_error;
+		}
+
+		if (!PageUptodate(page)) {
+			if (iocb->ki_flags & IOCB_WAITQ) {
+				if (written) {
+					put_page(page);
+					goto out;
+				}
+				error = lock_page_async(page, iocb->ki_waitq);
+			} else {
+				error = lock_page_killable(page);
+			}
+
+			if (unlikely(error))
+				goto readpage_error;
+			if (!PageUptodate(page)) {
+				if (page->mapping == NULL) {
+					/*
+					 * invalidate_mapping_pages got it
+					 */
+					unlock_page(page);
+					put_page(page);
+					goto find_page;
+				}
+				unlock_page(page);
+				shrink_readahead_size_eio(ra);
+				error = -EIO;
+				goto readpage_error;
+			}
+			unlock_page(page);
+		}
+
+		goto page_ok;
+
+readpage_error:
+		/* UHHUH! A synchronous read error occurred. Report it */
+		put_page(page);
+		goto out;
+
+no_cached_page:
+		/*
+		 * Ok, it wasn't cached, so we need to create a new
+		 * page..
+		 */
+		page = page_cache_alloc(mapping);
+		if (!page) {
+			error = -ENOMEM;
+			goto out;
+		}
+		error = add_to_page_cache_lru(page, mapping, index,
+				mapping_gfp_constraint(mapping, GFP_KERNEL));
+		if (error) {
+			put_page(page);
+			if (error == -EEXIST) {
+				error = 0;
+				goto find_page;
+			}
+			goto out;
+		}
+		goto readpage;
+	}
+
+would_block:
+	error = -EAGAIN;
+out:
+	ra->prev_pos = prev_index;
+	ra->prev_pos <<= PAGE_SHIFT;
+	ra->prev_pos |= prev_offset;
+
+	*ppos = ((loff_t)index << PAGE_SHIFT) + offset;
+	file_accessed(filp);
+	return written ? written : error;
+}
+EXPORT_SYMBOL_GPL(generic_file_buffered_read);
+
+/**
+ * generic_file_read_iter - generic filesystem read routine
+ * @iocb:	kernel I/O control block
+ * @iter:	destination for the data read
+ *
+ * This is the "read_iter()" routine for all filesystems
+ * that can use the page cache directly.
+ *
+ * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall
+ * be returned when no data can be read without waiting for I/O requests
+ * to complete; it doesn't prevent readahead.
+ *
+ * The IOCB_NOIO flag in iocb->ki_flags indicates that no new I/O
+ * requests shall be made for the read or for readahead.  When no data
+ * can be read, -EAGAIN shall be returned.  When readahead would be
+ * triggered, a partial, possibly empty read shall be returned.
+ *
+ * Return:
+ * * number of bytes copied, even for partial reads
+ * * negative error code (or 0 if IOCB_NOIO) if nothing was read
+ */
+ssize_t
+generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	size_t count = iov_iter_count(iter);
+	ssize_t retval = 0;
+
+	if (!count)
+		goto out; /* skip atime */
+
+	if (iocb->ki_flags & IOCB_DIRECT) {
+		struct file *file = iocb->ki_filp;
+		struct address_space *mapping = file->f_mapping;
+		struct inode *inode = mapping->host;
+		loff_t size;
+
+		size = i_size_read(inode);
+		if (iocb->ki_flags & IOCB_NOWAIT) {
+			if (filemap_range_has_page(mapping, iocb->ki_pos,
+						   iocb->ki_pos + count - 1))
+				return -EAGAIN;
+		} else {
+			retval = filemap_write_and_wait_range(mapping,
+						iocb->ki_pos,
+					        iocb->ki_pos + count - 1);
+			if (retval < 0)
+				goto out;
+		}
+
+		file_accessed(file);
+
+		retval = mapping->a_ops->direct_IO(iocb, iter);
+		if (retval >= 0) {
+			iocb->ki_pos += retval;
+			count -= retval;
+		}
+		iov_iter_revert(iter, count - iov_iter_count(iter));
+
+		/*
+		 * Btrfs can have a short DIO read if we encounter
+		 * compressed extents, so if there was an error, or if
+		 * we've already read everything we wanted to, or if
+		 * there was a short read because we hit EOF, go ahead
+		 * and return.  Otherwise fallthrough to buffered io for
+		 * the rest of the read.  Buffered reads will not work for
+		 * DAX files, so don't bother trying.
+		 */
+		if (retval < 0 || !count || iocb->ki_pos >= size ||
+		    IS_DAX(inode))
+			goto out;
+	}
+
+	retval = generic_file_buffered_read(iocb, iter, retval);
+out:
+	return retval;
+}
+EXPORT_SYMBOL(generic_file_read_iter);
+
+#ifdef CONFIG_MMU
+#define MMAP_LOTSAMISS  (100)
+/*
+ * lock_page_maybe_drop_mmap - lock the page, possibly dropping the mmap_lock
+ * @vmf - the vm_fault for this fault.
+ * @page - the page to lock.
+ * @fpin - the pointer to the file we may pin (or is already pinned).
+ *
+ * This works similar to lock_page_or_retry in that it can drop the mmap_lock.
+ * It differs in that it actually returns the page locked if it returns 1 and 0
+ * if it couldn't lock the page.  If we did have to drop the mmap_lock then fpin
+ * will point to the pinned file and needs to be fput()'ed at a later point.
+ */
+static int lock_page_maybe_drop_mmap(struct vm_fault *vmf, struct page *page,
+				     struct file **fpin)
+{
+	if (trylock_page(page))
+		return 1;
+
+	/*
+	 * NOTE! This will make us return with VM_FAULT_RETRY, but with
+	 * the mmap_lock still held. That's how FAULT_FLAG_RETRY_NOWAIT
+	 * is supposed to work. We have way too many special cases..
+	 */
+	if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
+		return 0;
+
+	*fpin = maybe_unlock_mmap_for_io(vmf, *fpin);
+	if (vmf->flags & FAULT_FLAG_KILLABLE) {
+		if (__lock_page_killable(page)) {
+			/*
+			 * We didn't have the right flags to drop the mmap_lock,
+			 * but all fault_handlers only check for fatal signals
+			 * if we return VM_FAULT_RETRY, so we need to drop the
+			 * mmap_lock here and return 0 if we don't have a fpin.
+			 */
+			if (*fpin == NULL)
+				mmap_read_unlock(vmf->vma->vm_mm);
+			return 0;
+		}
+	} else
+		__lock_page(page);
+	return 1;
+}
+
+
+/*
+ * Synchronous readahead happens when we don't even find a page in the page
+ * cache at all.  We don't want to perform IO under the mmap sem, so if we have
+ * to drop the mmap sem we return the file that was pinned in order for us to do
+ * that.  If we didn't pin a file then we return NULL.  The file that is
+ * returned needs to be fput()'ed when we're done with it.
+ */
+static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
+{
+	struct file *file = vmf->vma->vm_file;
+	struct file_ra_state *ra = &file->f_ra;
+	struct address_space *mapping = file->f_mapping;
+	DEFINE_READAHEAD(ractl, file, mapping, vmf->pgoff);
+	struct file *fpin = NULL;
+	unsigned int mmap_miss;
+
+	/* If we don't want any read-ahead, don't bother */
+	if (vmf->vma->vm_flags & VM_RAND_READ)
+		return fpin;
+	if (!ra->ra_pages)
+		return fpin;
+
+	if (vmf->vma->vm_flags & VM_SEQ_READ) {
+		fpin = maybe_unlock_mmap_for_io(vmf, fpin);
+		page_cache_sync_ra(&ractl, ra, ra->ra_pages);
+		return fpin;
+	}
+
+	/* Avoid banging the cache line if not needed */
+	mmap_miss = READ_ONCE(ra->mmap_miss);
+	if (mmap_miss < MMAP_LOTSAMISS * 10)
+		WRITE_ONCE(ra->mmap_miss, ++mmap_miss);
+
+	/*
+	 * Do we miss much more than hit in this file? If so,
+	 * stop bothering with read-ahead. It will only hurt.
+	 */
+	if (mmap_miss > MMAP_LOTSAMISS)
+		return fpin;
+
+	/*
+	 * mmap read-around
+	 */
+	fpin = maybe_unlock_mmap_for_io(vmf, fpin);
+	ra->start = max_t(long, 0, vmf->pgoff - ra->ra_pages / 2);
+	ra->size = ra->ra_pages;
+	ra->async_size = ra->ra_pages / 4;
+	ractl._index = ra->start;
+	do_page_cache_ra(&ractl, ra->size, ra->async_size);
+	return fpin;
+}
+
+/*
+ * Asynchronous readahead happens when we find the page and PG_readahead,
+ * so we want to possibly extend the readahead further.  We return the file that
+ * was pinned if we have to drop the mmap_lock in order to do IO.
+ */
+static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
+					    struct page *page)
+{
+	struct file *file = vmf->vma->vm_file;
+	struct file_ra_state *ra = &file->f_ra;
+	struct address_space *mapping = file->f_mapping;
+	struct file *fpin = NULL;
+	unsigned int mmap_miss;
+	pgoff_t offset = vmf->pgoff;
+
+	/* If we don't want any read-ahead, don't bother */
+	if (vmf->vma->vm_flags & VM_RAND_READ || !ra->ra_pages)
+		return fpin;
+	mmap_miss = READ_ONCE(ra->mmap_miss);
+	if (mmap_miss)
+		WRITE_ONCE(ra->mmap_miss, --mmap_miss);
+	if (PageReadahead(page)) {
+		fpin = maybe_unlock_mmap_for_io(vmf, fpin);
+		page_cache_async_readahead(mapping, ra, file,
+					   page, offset, ra->ra_pages);
+	}
+	return fpin;
+}
+
+/**
+ * filemap_fault - read in file data for page fault handling
+ * @vmf:	struct vm_fault containing details of the fault
+ *
+ * filemap_fault() is invoked via the vma operations vector for a
+ * mapped memory region to read in file data during a page fault.
+ *
+ * The goto's are kind of ugly, but this streamlines the normal case of having
+ * it in the page cache, and handles the special cases reasonably without
+ * having a lot of duplicated code.
+ *
+ * vma->vm_mm->mmap_lock must be held on entry.
+ *
+ * If our return value has VM_FAULT_RETRY set, it's because the mmap_lock
+ * may be dropped before doing I/O or by lock_page_maybe_drop_mmap().
+ *
+ * If our return value does not have VM_FAULT_RETRY set, the mmap_lock
+ * has not been released.
+ *
+ * We never return with VM_FAULT_RETRY and a bit from VM_FAULT_ERROR set.
+ *
+ * Return: bitwise-OR of %VM_FAULT_ codes.
+ */
+vm_fault_t filemap_fault(struct vm_fault *vmf)
+{
+	int error;
+	struct file *file = vmf->vma->vm_file;
+	struct file *fpin = NULL;
+	struct address_space *mapping = file->f_mapping;
+	struct file_ra_state *ra = &file->f_ra;
+	struct inode *inode = mapping->host;
+	pgoff_t offset = vmf->pgoff;
+	pgoff_t max_off;
+	struct page *page;
+	vm_fault_t ret = 0;
+
+	max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
+	if (unlikely(offset >= max_off))
+		return VM_FAULT_SIGBUS;
+
+	/*
+	 * Do we have something in the page cache already?
+	 */
+	page = find_get_page(mapping, offset);
+	if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
+		/*
+		 * We found the page, so try async readahead before
+		 * waiting for the lock.
+		 */
+		fpin = do_async_mmap_readahead(vmf, page);
+	} else if (!page) {
+		/* No page in the page cache at all */
+		count_vm_event(PGMAJFAULT);
+		count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
+		ret = VM_FAULT_MAJOR;
+		fpin = do_sync_mmap_readahead(vmf);
+retry_find:
+		page = pagecache_get_page(mapping, offset,
+					  FGP_CREAT|FGP_FOR_MMAP,
+					  vmf->gfp_mask);
+		if (!page) {
+			if (fpin)
+				goto out_retry;
+			return VM_FAULT_OOM;
+		}
+	}
+
+	if (!lock_page_maybe_drop_mmap(vmf, page, &fpin))
+		goto out_retry;
+
+	/* Did it get truncated? */
+	if (unlikely(compound_head(page)->mapping != mapping)) {
+		unlock_page(page);
+		put_page(page);
+		goto retry_find;
+	}
+	VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page);
+
+	/*
+	 * We have a locked page in the page cache, now we need to check
+	 * that it's up-to-date. If not, it is going to be due to an error.
+	 */
+	if (unlikely(!PageUptodate(page)))
+		goto page_not_uptodate;
+
+	/*
+	 * We've made it this far and we had to drop our mmap_lock, now is the
+	 * time to return to the upper layer and have it re-find the vma and
+	 * redo the fault.
+	 */
+	if (fpin) {
+		unlock_page(page);
+		goto out_retry;
+	}
+
+	/*
+	 * Found the page and have a reference on it.
+	 * We must recheck i_size under page lock.
+	 */
+	max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
+	if (unlikely(offset >= max_off)) {
+		unlock_page(page);
+		put_page(page);
+		return VM_FAULT_SIGBUS;
+	}
+
+	vmf->page = page;
+	return ret | VM_FAULT_LOCKED;
+
+page_not_uptodate:
+	/*
+	 * Umm, take care of errors if the page isn't up-to-date.
+	 * Try to re-read it _once_. We do this synchronously,
+	 * because there really aren't any performance issues here
+	 * and we need to check for errors.
+	 */
+	ClearPageError(page);
+	fpin = maybe_unlock_mmap_for_io(vmf, fpin);
+	error = mapping->a_ops->readpage(file, page);
+	if (!error) {
+		wait_on_page_locked(page);
+		if (!PageUptodate(page))
+			error = -EIO;
+	}
+	if (fpin)
+		goto out_retry;
+	put_page(page);
+
+	if (!error || error == AOP_TRUNCATED_PAGE)
+		goto retry_find;
+
+	shrink_readahead_size_eio(ra);
+	return VM_FAULT_SIGBUS;
+
+out_retry:
+	/*
+	 * We dropped the mmap_lock, we need to return to the fault handler to
+	 * re-find the vma and come back and find our hopefully still populated
+	 * page.
+	 */
+	if (page)
+		put_page(page);
+	if (fpin)
+		fput(fpin);
+	return ret | VM_FAULT_RETRY;
+}
+EXPORT_SYMBOL(filemap_fault);
+
+void filemap_map_pages(struct vm_fault *vmf,
+		pgoff_t start_pgoff, pgoff_t end_pgoff)
+{
+	struct file *file = vmf->vma->vm_file;
+	struct address_space *mapping = file->f_mapping;
+	pgoff_t last_pgoff = start_pgoff;
+	unsigned long max_idx;
+	XA_STATE(xas, &mapping->i_pages, start_pgoff);
+	struct page *head, *page;
+	unsigned int mmap_miss = READ_ONCE(file->f_ra.mmap_miss);
+
+	rcu_read_lock();
+	xas_for_each(&xas, head, end_pgoff) {
+		if (xas_retry(&xas, head))
+			continue;
+		if (xa_is_value(head))
+			goto next;
+
+		/*
+		 * Check for a locked page first, as a speculative
+		 * reference may adversely influence page migration.
+		 */
+		if (PageLocked(head))
+			goto next;
+		if (!page_cache_get_speculative(head))
+			goto next;
+
+		/* Has the page moved or been split? */
+		if (unlikely(head != xas_reload(&xas)))
+			goto skip;
+		page = find_subpage(head, xas.xa_index);
+
+		if (!PageUptodate(head) ||
+				PageReadahead(page) ||
+				PageHWPoison(page))
+			goto skip;
+		if (!trylock_page(head))
+			goto skip;
+
+		if (head->mapping != mapping || !PageUptodate(head))
+			goto unlock;
+
+		max_idx = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
+		if (xas.xa_index >= max_idx)
+			goto unlock;
+
+		if (mmap_miss > 0)
+			mmap_miss--;
+
+		vmf->address += (xas.xa_index - last_pgoff) << PAGE_SHIFT;
+		if (vmf->pte)
+			vmf->pte += xas.xa_index - last_pgoff;
+		last_pgoff = xas.xa_index;
+		if (alloc_set_pte(vmf, page))
+			goto unlock;
+		unlock_page(head);
+		goto next;
+unlock:
+		unlock_page(head);
+skip:
+		put_page(head);
+next:
+		/* Huge page is mapped? No need to proceed. */
+		if (pmd_trans_huge(*vmf->pmd))
+			break;
+	}
+	rcu_read_unlock();
+	WRITE_ONCE(file->f_ra.mmap_miss, mmap_miss);
+}
+EXPORT_SYMBOL(filemap_map_pages);
+
+vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf)
+{
+	struct page *page = vmf->page;
+	struct inode *inode = file_inode(vmf->vma->vm_file);
+	vm_fault_t ret = VM_FAULT_LOCKED;
+
+	sb_start_pagefault(inode->i_sb);
+	file_update_time(vmf->vma->vm_file);
+	lock_page(page);
+	if (page->mapping != inode->i_mapping) {
+		unlock_page(page);
+		ret = VM_FAULT_NOPAGE;
+		goto out;
+	}
+	/*
+	 * We mark the page dirty already here so that when freeze is in
+	 * progress, we are guaranteed that writeback during freezing will
+	 * see the dirty page and writeprotect it again.
+	 */
+	set_page_dirty(page);
+	wait_for_stable_page(page);
+out:
+	sb_end_pagefault(inode->i_sb);
+	return ret;
+}
+
+const struct vm_operations_struct generic_file_vm_ops = {
+	.fault		= filemap_fault,
+	.map_pages	= filemap_map_pages,
+	.page_mkwrite	= filemap_page_mkwrite,
+};
+
+/* This is used for a general mmap of a disk file */
+
+int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
+{
+	struct address_space *mapping = file->f_mapping;
+
+	if (!mapping->a_ops->readpage)
+		return -ENOEXEC;
+	file_accessed(file);
+	vma->vm_ops = &generic_file_vm_ops;
+	return 0;
+}
+
+/*
+ * This is for filesystems which do not implement ->writepage.
+ */
+int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
+		return -EINVAL;
+	return generic_file_mmap(file, vma);
+}
+#else
+vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf)
+{
+	return VM_FAULT_SIGBUS;
+}
+int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
+{
+	return -ENOSYS;
+}
+int generic_file_readonly_mmap(struct file * file, struct vm_area_struct * vma)
+{
+	return -ENOSYS;
+}
+#endif /* CONFIG_MMU */
+
+EXPORT_SYMBOL(filemap_page_mkwrite);
+EXPORT_SYMBOL(generic_file_mmap);
+EXPORT_SYMBOL(generic_file_readonly_mmap);
+
+static struct page *wait_on_page_read(struct page *page)
+{
+	if (!IS_ERR(page)) {
+		wait_on_page_locked(page);
+		if (!PageUptodate(page)) {
+			put_page(page);
+			page = ERR_PTR(-EIO);
+		}
+	}
+	return page;
+}
+
+static struct page *do_read_cache_page(struct address_space *mapping,
+				pgoff_t index,
+				int (*filler)(void *, struct page *),
+				void *data,
+				gfp_t gfp)
+{
+	struct page *page;
+	int err;
+repeat:
+	page = find_get_page(mapping, index);
+	if (!page) {
+		page = __page_cache_alloc(gfp);
+		if (!page)
+			return ERR_PTR(-ENOMEM);
+		err = add_to_page_cache_lru(page, mapping, index, gfp);
+		if (unlikely(err)) {
+			put_page(page);
+			if (err == -EEXIST)
+				goto repeat;
+			/* Presumably ENOMEM for xarray node */
+			return ERR_PTR(err);
+		}
+
+filler:
+		if (filler)
+			err = filler(data, page);
+		else
+			err = mapping->a_ops->readpage(data, page);
+
+		if (err < 0) {
+			put_page(page);
+			return ERR_PTR(err);
+		}
+
+		page = wait_on_page_read(page);
+		if (IS_ERR(page))
+			return page;
+		goto out;
+	}
+	if (PageUptodate(page))
+		goto out;
+
+	/*
+	 * Page is not up to date and may be locked due to one of the following
+	 * case a: Page is being filled and the page lock is held
+	 * case b: Read/write error clearing the page uptodate status
+	 * case c: Truncation in progress (page locked)
+	 * case d: Reclaim in progress
+	 *
+	 * Case a, the page will be up to date when the page is unlocked.
+	 *    There is no need to serialise on the page lock here as the page
+	 *    is pinned so the lock gives no additional protection. Even if the
+	 *    page is truncated, the data is still valid if PageUptodate as
+	 *    it's a race vs truncate race.
+	 * Case b, the page will not be up to date
+	 * Case c, the page may be truncated but in itself, the data may still
+	 *    be valid after IO completes as it's a read vs truncate race. The
+	 *    operation must restart if the page is not uptodate on unlock but
+	 *    otherwise serialising on page lock to stabilise the mapping gives
+	 *    no additional guarantees to the caller as the page lock is
+	 *    released before return.
+	 * Case d, similar to truncation. If reclaim holds the page lock, it
+	 *    will be a race with remove_mapping that determines if the mapping
+	 *    is valid on unlock but otherwise the data is valid and there is
+	 *    no need to serialise with page lock.
+	 *
+	 * As the page lock gives no additional guarantee, we optimistically
+	 * wait on the page to be unlocked and check if it's up to date and
+	 * use the page if it is. Otherwise, the page lock is required to
+	 * distinguish between the different cases. The motivation is that we
+	 * avoid spurious serialisations and wakeups when multiple processes
+	 * wait on the same page for IO to complete.
+	 */
+	wait_on_page_locked(page);
+	if (PageUptodate(page))
+		goto out;
+
+	/* Distinguish between all the cases under the safety of the lock */
+	lock_page(page);
+
+	/* Case c or d, restart the operation */
+	if (!page->mapping) {
+		unlock_page(page);
+		put_page(page);
+		goto repeat;
+	}
+
+	/* Someone else locked and filled the page in a very small window */
+	if (PageUptodate(page)) {
+		unlock_page(page);
+		goto out;
+	}
+
+	/*
+	 * A previous I/O error may have been due to temporary
+	 * failures.
+	 * Clear page error before actual read, PG_error will be
+	 * set again if read page fails.
+	 */
+	ClearPageError(page);
+	goto filler;
+
+out:
+	mark_page_accessed(page);
+	return page;
+}
+
+/**
+ * read_cache_page - read into page cache, fill it if needed
+ * @mapping:	the page's address_space
+ * @index:	the page index
+ * @filler:	function to perform the read
+ * @data:	first arg to filler(data, page) function, often left as NULL
+ *
+ * Read into the page cache. If a page already exists, and PageUptodate() is
+ * not set, try to fill the page and wait for it to become unlocked.
+ *
+ * If the page does not get brought uptodate, return -EIO.
+ *
+ * Return: up to date page on success, ERR_PTR() on failure.
+ */
+struct page *read_cache_page(struct address_space *mapping,
+				pgoff_t index,
+				int (*filler)(void *, struct page *),
+				void *data)
+{
+	return do_read_cache_page(mapping, index, filler, data,
+			mapping_gfp_mask(mapping));
+}
+EXPORT_SYMBOL(read_cache_page);
+
+/**
+ * read_cache_page_gfp - read into page cache, using specified page allocation flags.
+ * @mapping:	the page's address_space
+ * @index:	the page index
+ * @gfp:	the page allocator flags to use if allocating
+ *
+ * This is the same as "read_mapping_page(mapping, index, NULL)", but with
+ * any new page allocations done using the specified allocation flags.
+ *
+ * If the page does not get brought uptodate, return -EIO.
+ *
+ * Return: up to date page on success, ERR_PTR() on failure.
+ */
+struct page *read_cache_page_gfp(struct address_space *mapping,
+				pgoff_t index,
+				gfp_t gfp)
+{
+	return do_read_cache_page(mapping, index, NULL, NULL, gfp);
+}
+EXPORT_SYMBOL(read_cache_page_gfp);
+
+int pagecache_write_begin(struct file *file, struct address_space *mapping,
+				loff_t pos, unsigned len, unsigned flags,
+				struct page **pagep, void **fsdata)
+{
+	const struct address_space_operations *aops = mapping->a_ops;
+
+	return aops->write_begin(file, mapping, pos, len, flags,
+							pagep, fsdata);
+}
+EXPORT_SYMBOL(pagecache_write_begin);
+
+int pagecache_write_end(struct file *file, struct address_space *mapping,
+				loff_t pos, unsigned len, unsigned copied,
+				struct page *page, void *fsdata)
+{
+	const struct address_space_operations *aops = mapping->a_ops;
+
+	return aops->write_end(file, mapping, pos, len, copied, page, fsdata);
+}
+EXPORT_SYMBOL(pagecache_write_end);
+
+/*
+ * Warn about a page cache invalidation failure during a direct I/O write.
+ */
+void dio_warn_stale_pagecache(struct file *filp)
+{
+	static DEFINE_RATELIMIT_STATE(_rs, 86400 * HZ, DEFAULT_RATELIMIT_BURST);
+	char pathname[128];
+	struct inode *inode = file_inode(filp);
+	char *path;
+
+	errseq_set(&inode->i_mapping->wb_err, -EIO);
+	if (__ratelimit(&_rs)) {
+		path = file_path(filp, pathname, sizeof(pathname));
+		if (IS_ERR(path))
+			path = "(unknown)";
+		pr_crit("Page cache invalidation failure on direct I/O.  Possible data corruption due to collision with buffered I/O!\n");
+		pr_crit("File: %s PID: %d Comm: %.20s\n", path, current->pid,
+			current->comm);
+	}
+}
+
+ssize_t
+generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct file	*file = iocb->ki_filp;
+	struct address_space *mapping = file->f_mapping;
+	struct inode	*inode = mapping->host;
+	loff_t		pos = iocb->ki_pos;
+	ssize_t		written;
+	size_t		write_len;
+	pgoff_t		end;
+
+	write_len = iov_iter_count(from);
+	end = (pos + write_len - 1) >> PAGE_SHIFT;
+
+	if (iocb->ki_flags & IOCB_NOWAIT) {
+		/* If there are pages to writeback, return */
+		if (filemap_range_has_page(inode->i_mapping, pos,
+					   pos + write_len - 1))
+			return -EAGAIN;
+	} else {
+		written = filemap_write_and_wait_range(mapping, pos,
+							pos + write_len - 1);
+		if (written)
+			goto out;
+	}
+
+	/*
+	 * After a write we want buffered reads to be sure to go to disk to get
+	 * the new data.  We invalidate clean cached page from the region we're
+	 * about to write.  We do this *before* the write so that we can return
+	 * without clobbering -EIOCBQUEUED from ->direct_IO().
+	 */
+	written = invalidate_inode_pages2_range(mapping,
+					pos >> PAGE_SHIFT, end);
+	/*
+	 * If a page can not be invalidated, return 0 to fall back
+	 * to buffered write.
+	 */
+	if (written) {
+		if (written == -EBUSY)
+			return 0;
+		goto out;
+	}
+
+	written = mapping->a_ops->direct_IO(iocb, from);
+
+	/*
+	 * Finally, try again to invalidate clean pages which might have been
+	 * cached by non-direct readahead, or faulted in by get_user_pages()
+	 * if the source of the write was an mmap'ed region of the file
+	 * we're writing.  Either one is a pretty crazy thing to do,
+	 * so we don't support it 100%.  If this invalidation
+	 * fails, tough, the write still worked...
+	 *
+	 * Most of the time we do not need this since dio_complete() will do
+	 * the invalidation for us. However there are some file systems that
+	 * do not end up with dio_complete() being called, so let's not break
+	 * them by removing it completely.
+	 *
+	 * Noticeable example is a blkdev_direct_IO().
+	 *
+	 * Skip invalidation for async writes or if mapping has no pages.
+	 */
+	if (written > 0 && mapping->nrpages &&
+	    invalidate_inode_pages2_range(mapping, pos >> PAGE_SHIFT, end))
+		dio_warn_stale_pagecache(file);
+
+	if (written > 0) {
+		pos += written;
+		write_len -= written;
+		if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
+			i_size_write(inode, pos);
+			mark_inode_dirty(inode);
+		}
+		iocb->ki_pos = pos;
+	}
+	iov_iter_revert(from, write_len - iov_iter_count(from));
+out:
+	return written;
+}
+EXPORT_SYMBOL(generic_file_direct_write);
+
+/*
+ * Find or create a page at the given pagecache position. Return the locked
+ * page. This function is specifically for buffered writes.
+ */
+struct page *grab_cache_page_write_begin(struct address_space *mapping,
+					pgoff_t index, unsigned flags)
+{
+	struct page *page;
+	int fgp_flags = FGP_LOCK|FGP_WRITE|FGP_CREAT;
+
+	if (flags & AOP_FLAG_NOFS)
+		fgp_flags |= FGP_NOFS;
+
+	page = pagecache_get_page(mapping, index, fgp_flags,
+			mapping_gfp_mask(mapping));
+	if (page)
+		wait_for_stable_page(page);
+
+	return page;
+}
+EXPORT_SYMBOL(grab_cache_page_write_begin);
+
+ssize_t generic_perform_write(struct file *file,
+				struct iov_iter *i, loff_t pos)
+{
+	struct address_space *mapping = file->f_mapping;
+	const struct address_space_operations *a_ops = mapping->a_ops;
+	long status = 0;
+	ssize_t written = 0;
+	unsigned int flags = 0;
+
+	do {
+		struct page *page;
+		unsigned long offset;	/* Offset into pagecache page */
+		unsigned long bytes;	/* Bytes to write to page */
+		size_t copied;		/* Bytes copied from user */
+		void *fsdata = NULL;
+
+		offset = (pos & (PAGE_SIZE - 1));
+		bytes = min_t(unsigned long, PAGE_SIZE - offset,
+						iov_iter_count(i));
+
+again:
+		/*
+		 * Bring in the user page that we will copy from _first_.
+		 * Otherwise there's a nasty deadlock on copying from the
+		 * same page as we're writing to, without it being marked
+		 * up-to-date.
+		 *
+		 * Not only is this an optimisation, but it is also required
+		 * to check that the address is actually valid, when atomic
+		 * usercopies are used, below.
+		 */
+		if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
+			status = -EFAULT;
+			break;
+		}
+
+		if (fatal_signal_pending(current)) {
+			status = -EINTR;
+			break;
+		}
+
+		status = a_ops->write_begin(file, mapping, pos, bytes, flags,
+						&page, &fsdata);
+		if (unlikely(status < 0))
+			break;
+
+		if (mapping_writably_mapped(mapping))
+			flush_dcache_page(page);
+
+		copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
+		flush_dcache_page(page);
+
+		status = a_ops->write_end(file, mapping, pos, bytes, copied,
+						page, fsdata);
+		if (unlikely(status < 0))
+			break;
+		copied = status;
+
+		cond_resched();
+
+		iov_iter_advance(i, copied);
+		if (unlikely(copied == 0)) {
+			/*
+			 * If we were unable to copy any data at all, we must
+			 * fall back to a single segment length write.
+			 *
+			 * If we didn't fallback here, we could livelock
+			 * because not all segments in the iov can be copied at
+			 * once without a pagefault.
+			 */
+			bytes = min_t(unsigned long, PAGE_SIZE - offset,
+						iov_iter_single_seg_count(i));
+			goto again;
+		}
+		pos += copied;
+		written += copied;
+
+		balance_dirty_pages_ratelimited(mapping);
+	} while (iov_iter_count(i));
+
+	return written ? written : status;
+}
+EXPORT_SYMBOL(generic_perform_write);
+
+/**
+ * __generic_file_write_iter - write data to a file
+ * @iocb:	IO state structure (file, offset, etc.)
+ * @from:	iov_iter with data to write
+ *
+ * This function does all the work needed for actually writing data to a
+ * file. It does all basic checks, removes SUID from the file, updates
+ * modification times and calls proper subroutines depending on whether we
+ * do direct IO or a standard buffered write.
+ *
+ * It expects i_mutex to be grabbed unless we work on a block device or similar
+ * object which does not need locking at all.
+ *
+ * This function does *not* take care of syncing data in case of O_SYNC write.
+ * A caller has to handle it. This is mainly due to the fact that we want to
+ * avoid syncing under i_mutex.
+ *
+ * Return:
+ * * number of bytes written, even for truncated writes
+ * * negative error code if no data has been written at all
+ */
+ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct file *file = iocb->ki_filp;
+	struct address_space * mapping = file->f_mapping;
+	struct inode 	*inode = mapping->host;
+	ssize_t		written = 0;
+	ssize_t		err;
+	ssize_t		status;
+
+	/* We can write back this queue in page reclaim */
+	current->backing_dev_info = inode_to_bdi(inode);
+	err = file_remove_privs(file);
+	if (err)
+		goto out;
+
+	err = file_update_time(file);
+	if (err)
+		goto out;
+
+	if (iocb->ki_flags & IOCB_DIRECT) {
+		loff_t pos, endbyte;
+
+		written = generic_file_direct_write(iocb, from);
+		/*
+		 * If the write stopped short of completing, fall back to
+		 * buffered writes.  Some filesystems do this for writes to
+		 * holes, for example.  For DAX files, a buffered write will
+		 * not succeed (even if it did, DAX does not handle dirty
+		 * page-cache pages correctly).
+		 */
+		if (written < 0 || !iov_iter_count(from) || IS_DAX(inode))
+			goto out;
+
+		status = generic_perform_write(file, from, pos = iocb->ki_pos);
+		/*
+		 * If generic_perform_write() returned a synchronous error
+		 * then we want to return the number of bytes which were
+		 * direct-written, or the error code if that was zero.  Note
+		 * that this differs from normal direct-io semantics, which
+		 * will return -EFOO even if some bytes were written.
+		 */
+		if (unlikely(status < 0)) {
+			err = status;
+			goto out;
+		}
+		/*
+		 * We need to ensure that the page cache pages are written to
+		 * disk and invalidated to preserve the expected O_DIRECT
+		 * semantics.
+		 */
+		endbyte = pos + status - 1;
+		err = filemap_write_and_wait_range(mapping, pos, endbyte);
+		if (err == 0) {
+			iocb->ki_pos = endbyte + 1;
+			written += status;
+			invalidate_mapping_pages(mapping,
+						 pos >> PAGE_SHIFT,
+						 endbyte >> PAGE_SHIFT);
+		} else {
+			/*
+			 * We don't know how much we wrote, so just return
+			 * the number of bytes which were direct-written
+			 */
+		}
+	} else {
+		written = generic_perform_write(file, from, iocb->ki_pos);
+		if (likely(written > 0))
+			iocb->ki_pos += written;
+	}
+out:
+	current->backing_dev_info = NULL;
+	return written ? written : err;
+}
+EXPORT_SYMBOL(__generic_file_write_iter);
+
+/**
+ * generic_file_write_iter - write data to a file
+ * @iocb:	IO state structure
+ * @from:	iov_iter with data to write
+ *
+ * This is a wrapper around __generic_file_write_iter() to be used by most
+ * filesystems. It takes care of syncing the file in case of O_SYNC file
+ * and acquires i_mutex as needed.
+ * Return:
+ * * negative error code if no data has been written at all of
+ *   vfs_fsync_range() failed for a synchronous write
+ * * number of bytes written, even for truncated writes
+ */
+ssize_t generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct file *file = iocb->ki_filp;
+	struct inode *inode = file->f_mapping->host;
+	ssize_t ret;
+
+	inode_lock(inode);
+	ret = generic_write_checks(iocb, from);
+	if (ret > 0)
+		ret = __generic_file_write_iter(iocb, from);
+	inode_unlock(inode);
+
+	if (ret > 0)
+		ret = generic_write_sync(iocb, ret);
+	return ret;
+}
+EXPORT_SYMBOL(generic_file_write_iter);
+
+/**
+ * try_to_release_page() - release old fs-specific metadata on a page
+ *
+ * @page: the page which the kernel is trying to free
+ * @gfp_mask: memory allocation flags (and I/O mode)
+ *
+ * The address_space is to try to release any data against the page
+ * (presumably at page->private).
+ *
+ * This may also be called if PG_fscache is set on a page, indicating that the
+ * page is known to the local caching routines.
+ *
+ * The @gfp_mask argument specifies whether I/O may be performed to release
+ * this page (__GFP_IO), and whether the call may block (__GFP_RECLAIM & __GFP_FS).
+ *
+ * Return: %1 if the release was successful, otherwise return zero.
+ */
+int try_to_release_page(struct page *page, gfp_t gfp_mask)
+{
+	struct address_space * const mapping = page->mapping;
+
+	BUG_ON(!PageLocked(page));
+	if (PageWriteback(page))
+		return 0;
+
+	if (mapping && mapping->a_ops->releasepage)
+		return mapping->a_ops->releasepage(page, gfp_mask);
+	return try_to_free_buffers(page);
+}
+
+EXPORT_SYMBOL(try_to_release_page);