1 files changed, 292 insertions, 0 deletions
diff --git a/fs/erofs/utils.c b/fs/erofs/utils.c
new file mode 100644
index 000000000..46627cb69
--- /dev/null
+++ b/fs/erofs/utils.c
@@ -0,0 +1,292 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2018 HUAWEI, Inc.
+ *             https://www.huawei.com/
+ */
+#include "internal.h"
+#include <linux/pagevec.h>
+
+struct page *erofs_allocpage(struct page **pagepool, gfp_t gfp)
+{
+	struct page *page = *pagepool;
+
+	if (page) {
+		DBG_BUGON(page_ref_count(page) != 1);
+		*pagepool = (struct page *)page_private(page);
+	} else {
+		page = alloc_page(gfp);
+	}
+	return page;
+}
+
+void erofs_release_pages(struct page **pagepool)
+{
+	while (*pagepool) {
+		struct page *page = *pagepool;
+
+		*pagepool = (struct page *)page_private(page);
+		put_page(page);
+	}
+}
+
+#ifdef CONFIG_EROFS_FS_ZIP
+/* global shrink count (for all mounted EROFS instances) */
+static atomic_long_t erofs_global_shrink_cnt;
+
+static int erofs_workgroup_get(struct erofs_workgroup *grp)
+{
+	int o;
+
+repeat:
+	o = erofs_wait_on_workgroup_freezed(grp);
+	if (o <= 0)
+		return -1;
+
+	if (atomic_cmpxchg(&grp->refcount, o, o + 1) != o)
+		goto repeat;
+
+	/* decrease refcount paired by erofs_workgroup_put */
+	if (o == 1)
+		atomic_long_dec(&erofs_global_shrink_cnt);
+	return 0;
+}
+
+struct erofs_workgroup *erofs_find_workgroup(struct super_block *sb,
+					     pgoff_t index)
+{
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+	struct erofs_workgroup *grp;
+
+repeat:
+	rcu_read_lock();
+	grp = xa_load(&sbi->managed_pslots, index);
+	if (grp) {
+		if (erofs_workgroup_get(grp)) {
+			/* prefer to relax rcu read side */
+			rcu_read_unlock();
+			goto repeat;
+		}
+
+		DBG_BUGON(index != grp->index);
+	}
+	rcu_read_unlock();
+	return grp;
+}
+
+struct erofs_workgroup *erofs_insert_workgroup(struct super_block *sb,
+					       struct erofs_workgroup *grp)
+{
+	struct erofs_sb_info *const sbi = EROFS_SB(sb);
+	struct erofs_workgroup *pre;
+
+	/*
+	 * Bump up a reference count before making this visible
+	 * to others for the XArray in order to avoid potential
+	 * UAF without serialized by xa_lock.
+	 */
+	atomic_inc(&grp->refcount);
+
+repeat:
+	xa_lock(&sbi->managed_pslots);
+	pre = __xa_cmpxchg(&sbi->managed_pslots, grp->index,
+			   NULL, grp, GFP_NOFS);
+	if (pre) {
+		if (xa_is_err(pre)) {
+			pre = ERR_PTR(xa_err(pre));
+		} else if (erofs_workgroup_get(pre)) {
+			/* try to legitimize the current in-tree one */
+			xa_unlock(&sbi->managed_pslots);
+			cond_resched();
+			goto repeat;
+		}
+		atomic_dec(&grp->refcount);
+		grp = pre;
+	}
+	xa_unlock(&sbi->managed_pslots);
+	return grp;
+}
+
+static void  __erofs_workgroup_free(struct erofs_workgroup *grp)
+{
+	atomic_long_dec(&erofs_global_shrink_cnt);
+	erofs_workgroup_free_rcu(grp);
+}
+
+int erofs_workgroup_put(struct erofs_workgroup *grp)
+{
+	int count = atomic_dec_return(&grp->refcount);
+
+	if (count == 1)
+		atomic_long_inc(&erofs_global_shrink_cnt);
+	else if (!count)
+		__erofs_workgroup_free(grp);
+	return count;
+}
+
+static bool erofs_try_to_release_workgroup(struct erofs_sb_info *sbi,
+					   struct erofs_workgroup *grp)
+{
+	/*
+	 * If managed cache is on, refcount of workgroups
+	 * themselves could be < 0 (freezed). In other words,
+	 * there is no guarantee that all refcounts > 0.
+	 */
+	if (!erofs_workgroup_try_to_freeze(grp, 1))
+		return false;
+
+	/*
+	 * Note that all cached pages should be unattached
+	 * before deleted from the XArray. Otherwise some
+	 * cached pages could be still attached to the orphan
+	 * old workgroup when the new one is available in the tree.
+	 */
+	if (erofs_try_to_free_all_cached_pages(sbi, grp)) {
+		erofs_workgroup_unfreeze(grp, 1);
+		return false;
+	}
+
+	/*
+	 * It's impossible to fail after the workgroup is freezed,
+	 * however in order to avoid some race conditions, add a
+	 * DBG_BUGON to observe this in advance.
+	 */
+	DBG_BUGON(__xa_erase(&sbi->managed_pslots, grp->index) != grp);
+
+	/* last refcount should be connected with its managed pslot.  */
+	erofs_workgroup_unfreeze(grp, 0);
+	__erofs_workgroup_free(grp);
+	return true;
+}
+
+static unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
+					      unsigned long nr_shrink)
+{
+	struct erofs_workgroup *grp;
+	unsigned int freed = 0;
+	unsigned long index;
+
+	xa_lock(&sbi->managed_pslots);
+	xa_for_each(&sbi->managed_pslots, index, grp) {
+		/* try to shrink each valid workgroup */
+		if (!erofs_try_to_release_workgroup(sbi, grp))
+			continue;
+		xa_unlock(&sbi->managed_pslots);
+
+		++freed;
+		if (!--nr_shrink)
+			return freed;
+		xa_lock(&sbi->managed_pslots);
+	}
+	xa_unlock(&sbi->managed_pslots);
+	return freed;
+}
+
+/* protected by 'erofs_sb_list_lock' */
+static unsigned int shrinker_run_no;
+
+/* protects the mounted 'erofs_sb_list' */
+static DEFINE_SPINLOCK(erofs_sb_list_lock);
+static LIST_HEAD(erofs_sb_list);
+
+void erofs_shrinker_register(struct super_block *sb)
+{
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+
+	mutex_init(&sbi->umount_mutex);
+
+	spin_lock(&erofs_sb_list_lock);
+	list_add(&sbi->list, &erofs_sb_list);
+	spin_unlock(&erofs_sb_list_lock);
+}
+
+void erofs_shrinker_unregister(struct super_block *sb)
+{
+	struct erofs_sb_info *const sbi = EROFS_SB(sb);
+
+	mutex_lock(&sbi->umount_mutex);
+	/* clean up all remaining workgroups in memory */
+	erofs_shrink_workstation(sbi, ~0UL);
+
+	spin_lock(&erofs_sb_list_lock);
+	list_del(&sbi->list);
+	spin_unlock(&erofs_sb_list_lock);
+	mutex_unlock(&sbi->umount_mutex);
+}
+
+static unsigned long erofs_shrink_count(struct shrinker *shrink,
+					struct shrink_control *sc)
+{
+	return atomic_long_read(&erofs_global_shrink_cnt);
+}
+
+static unsigned long erofs_shrink_scan(struct shrinker *shrink,
+				       struct shrink_control *sc)
+{
+	struct erofs_sb_info *sbi;
+	struct list_head *p;
+
+	unsigned long nr = sc->nr_to_scan;
+	unsigned int run_no;
+	unsigned long freed = 0;
+
+	spin_lock(&erofs_sb_list_lock);
+	do {
+		run_no = ++shrinker_run_no;
+	} while (run_no == 0);
+
+	/* Iterate over all mounted superblocks and try to shrink them */
+	p = erofs_sb_list.next;
+	while (p != &erofs_sb_list) {
+		sbi = list_entry(p, struct erofs_sb_info, list);
+
+		/*
+		 * We move the ones we do to the end of the list, so we stop
+		 * when we see one we have already done.
+		 */
+		if (sbi->shrinker_run_no == run_no)
+			break;
+
+		if (!mutex_trylock(&sbi->umount_mutex)) {
+			p = p->next;
+			continue;
+		}
+
+		spin_unlock(&erofs_sb_list_lock);
+		sbi->shrinker_run_no = run_no;
+
+		freed += erofs_shrink_workstation(sbi, nr - freed);
+
+		spin_lock(&erofs_sb_list_lock);
+		/* Get the next list element before we move this one */
+		p = p->next;
+
+		/*
+		 * Move this one to the end of the list to provide some
+		 * fairness.
+		 */
+		list_move_tail(&sbi->list, &erofs_sb_list);
+		mutex_unlock(&sbi->umount_mutex);
+
+		if (freed >= nr)
+			break;
+	}
+	spin_unlock(&erofs_sb_list_lock);
+	return freed;
+}
+
+static struct shrinker erofs_shrinker_info = {
+	.scan_objects = erofs_shrink_scan,
+	.count_objects = erofs_shrink_count,
+	.seeks = DEFAULT_SEEKS,
+};
+
+int __init erofs_init_shrinker(void)
+{
+	return register_shrinker(&erofs_shrinker_info, "erofs-shrinker");
+}
+
+void erofs_exit_shrinker(void)
+{
+	unregister_shrinker(&erofs_shrinker_info);
+}
+#endif	/* !CONFIG_EROFS_FS_ZIP */