Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 1239 insertions, 0 deletions

diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c
new file mode 100644
index 0000000000..64b3a1c76f
--- /dev/null
+++ b/drivers/block/drbd/drbd_actlog.c
@@ -0,0 +1,1239 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+   drbd_actlog.c
+
+   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
+
+   Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
+   Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>.
+   Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
+
+
+ */
+
+#include <linux/slab.h>
+#include <linux/crc32c.h>
+#include <linux/drbd.h>
+#include <linux/drbd_limits.h>
+#include "drbd_int.h"
+
+
+enum al_transaction_types {
+	AL_TR_UPDATE = 0,
+	AL_TR_INITIALIZED = 0xffff
+};
+/* all fields on disc in big endian */
+struct __packed al_transaction_on_disk {
+	/* don't we all like magic */
+	__be32	magic;
+
+	/* to identify the most recent transaction block
+	 * in the on disk ring buffer */
+	__be32	tr_number;
+
+	/* checksum on the full 4k block, with this field set to 0. */
+	__be32	crc32c;
+
+	/* type of transaction, special transaction types like:
+	 * purge-all, set-all-idle, set-all-active, ... to-be-defined
+	 * see also enum al_transaction_types */
+	__be16	transaction_type;
+
+	/* we currently allow only a few thousand extents,
+	 * so 16bit will be enough for the slot number. */
+
+	/* how many updates in this transaction */
+	__be16	n_updates;
+
+	/* maximum slot number, "al-extents" in drbd.conf speak.
+	 * Having this in each transaction should make reconfiguration
+	 * of that parameter easier. */
+	__be16	context_size;
+
+	/* slot number the context starts with */
+	__be16	context_start_slot_nr;
+
+	/* Some reserved bytes.  Expected usage is a 64bit counter of
+	 * sectors-written since device creation, and other data generation tag
+	 * supporting usage */
+	__be32	__reserved[4];
+
+	/* --- 36 byte used --- */
+
+	/* Reserve space for up to AL_UPDATES_PER_TRANSACTION changes
+	 * in one transaction, then use the remaining byte in the 4k block for
+	 * context information.  "Flexible" number of updates per transaction
+	 * does not help, as we have to account for the case when all update
+	 * slots are used anyways, so it would only complicate code without
+	 * additional benefit.
+	 */
+	__be16	update_slot_nr[AL_UPDATES_PER_TRANSACTION];
+
+	/* but the extent number is 32bit, which at an extent size of 4 MiB
+	 * allows to cover device sizes of up to 2**54 Byte (16 PiB) */
+	__be32	update_extent_nr[AL_UPDATES_PER_TRANSACTION];
+
+	/* --- 420 bytes used (36 + 64*6) --- */
+
+	/* 4096 - 420 = 3676 = 919 * 4 */
+	__be32	context[AL_CONTEXT_PER_TRANSACTION];
+};
+
+void *drbd_md_get_buffer(struct drbd_device *device, const char *intent)
+{
+	int r;
+
+	wait_event(device->misc_wait,
+		   (r = atomic_cmpxchg(&device->md_io.in_use, 0, 1)) == 0 ||
+		   device->state.disk <= D_FAILED);
+
+	if (r)
+		return NULL;
+
+	device->md_io.current_use = intent;
+	device->md_io.start_jif = jiffies;
+	device->md_io.submit_jif = device->md_io.start_jif - 1;
+	return page_address(device->md_io.page);
+}
+
+void drbd_md_put_buffer(struct drbd_device *device)
+{
+	if (atomic_dec_and_test(&device->md_io.in_use))
+		wake_up(&device->misc_wait);
+}
+
+void wait_until_done_or_force_detached(struct drbd_device *device, struct drbd_backing_dev *bdev,
+				     unsigned int *done)
+{
+	long dt;
+
+	rcu_read_lock();
+	dt = rcu_dereference(bdev->disk_conf)->disk_timeout;
+	rcu_read_unlock();
+	dt = dt * HZ / 10;
+	if (dt == 0)
+		dt = MAX_SCHEDULE_TIMEOUT;
+
+	dt = wait_event_timeout(device->misc_wait,
+			*done || test_bit(FORCE_DETACH, &device->flags), dt);
+	if (dt == 0) {
+		drbd_err(device, "meta-data IO operation timed out\n");
+		drbd_chk_io_error(device, 1, DRBD_FORCE_DETACH);
+	}
+}
+
+static int _drbd_md_sync_page_io(struct drbd_device *device,
+				 struct drbd_backing_dev *bdev,
+				 sector_t sector, enum req_op op)
+{
+	struct bio *bio;
+	/* we do all our meta data IO in aligned 4k blocks. */
+	const int size = 4096;
+	int err;
+	blk_opf_t op_flags = 0;
+
+	device->md_io.done = 0;
+	device->md_io.error = -ENODEV;
+
+	if ((op == REQ_OP_WRITE) && !test_bit(MD_NO_FUA, &device->flags))
+		op_flags |= REQ_FUA | REQ_PREFLUSH;
+	op_flags |= REQ_SYNC;
+
+	bio = bio_alloc_bioset(bdev->md_bdev, 1, op | op_flags, GFP_NOIO,
+			       &drbd_md_io_bio_set);
+	bio->bi_iter.bi_sector = sector;
+	err = -EIO;
+	if (bio_add_page(bio, device->md_io.page, size, 0) != size)
+		goto out;
+	bio->bi_private = device;
+	bio->bi_end_io = drbd_md_endio;
+
+	if (op != REQ_OP_WRITE && device->state.disk == D_DISKLESS && device->ldev == NULL)
+		/* special case, drbd_md_read() during drbd_adm_attach(): no get_ldev */
+		;
+	else if (!get_ldev_if_state(device, D_ATTACHING)) {
+		/* Corresponding put_ldev in drbd_md_endio() */
+		drbd_err(device, "ASSERT FAILED: get_ldev_if_state() == 1 in _drbd_md_sync_page_io()\n");
+		err = -ENODEV;
+		goto out;
+	}
+
+	bio_get(bio); /* one bio_put() is in the completion handler */
+	atomic_inc(&device->md_io.in_use); /* drbd_md_put_buffer() is in the completion handler */
+	device->md_io.submit_jif = jiffies;
+	if (drbd_insert_fault(device, (op == REQ_OP_WRITE) ? DRBD_FAULT_MD_WR : DRBD_FAULT_MD_RD))
+		bio_io_error(bio);
+	else
+		submit_bio(bio);
+	wait_until_done_or_force_detached(device, bdev, &device->md_io.done);
+	if (!bio->bi_status)
+		err = device->md_io.error;
+
+ out:
+	bio_put(bio);
+	return err;
+}
+
+int drbd_md_sync_page_io(struct drbd_device *device, struct drbd_backing_dev *bdev,
+			 sector_t sector, enum req_op op)
+{
+	int err;
+	D_ASSERT(device, atomic_read(&device->md_io.in_use) == 1);
+
+	BUG_ON(!bdev->md_bdev);
+
+	dynamic_drbd_dbg(device, "meta_data io: %s [%d]:%s(,%llus,%s) %pS\n",
+	     current->comm, current->pid, __func__,
+	     (unsigned long long)sector, (op == REQ_OP_WRITE) ? "WRITE" : "READ",
+	     (void*)_RET_IP_ );
+
+	if (sector < drbd_md_first_sector(bdev) ||
+	    sector + 7 > drbd_md_last_sector(bdev))
+		drbd_alert(device, "%s [%d]:%s(,%llus,%s) out of range md access!\n",
+		     current->comm, current->pid, __func__,
+		     (unsigned long long)sector,
+		     (op == REQ_OP_WRITE) ? "WRITE" : "READ");
+
+	err = _drbd_md_sync_page_io(device, bdev, sector, op);
+	if (err) {
+		drbd_err(device, "drbd_md_sync_page_io(,%llus,%s) failed with error %d\n",
+		    (unsigned long long)sector,
+		    (op == REQ_OP_WRITE) ? "WRITE" : "READ", err);
+	}
+	return err;
+}
+
+static struct bm_extent *find_active_resync_extent(struct drbd_device *device, unsigned int enr)
+{
+	struct lc_element *tmp;
+	tmp = lc_find(device->resync, enr/AL_EXT_PER_BM_SECT);
+	if (unlikely(tmp != NULL)) {
+		struct bm_extent  *bm_ext = lc_entry(tmp, struct bm_extent, lce);
+		if (test_bit(BME_NO_WRITES, &bm_ext->flags))
+			return bm_ext;
+	}
+	return NULL;
+}
+
+static struct lc_element *_al_get(struct drbd_device *device, unsigned int enr, bool nonblock)
+{
+	struct lc_element *al_ext;
+	struct bm_extent *bm_ext;
+	int wake;
+
+	spin_lock_irq(&device->al_lock);
+	bm_ext = find_active_resync_extent(device, enr);
+	if (bm_ext) {
+		wake = !test_and_set_bit(BME_PRIORITY, &bm_ext->flags);
+		spin_unlock_irq(&device->al_lock);
+		if (wake)
+			wake_up(&device->al_wait);
+		return NULL;
+	}
+	if (nonblock)
+		al_ext = lc_try_get(device->act_log, enr);
+	else
+		al_ext = lc_get(device->act_log, enr);
+	spin_unlock_irq(&device->al_lock);
+	return al_ext;
+}
+
+bool drbd_al_begin_io_fastpath(struct drbd_device *device, struct drbd_interval *i)
+{
+	/* for bios crossing activity log extent boundaries,
+	 * we may need to activate two extents in one go */
+	unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
+	unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);
+
+	D_ASSERT(device, first <= last);
+	D_ASSERT(device, atomic_read(&device->local_cnt) > 0);
+
+	/* FIXME figure out a fast path for bios crossing AL extent boundaries */
+	if (first != last)
+		return false;
+
+	return _al_get(device, first, true);
+}
+
+bool drbd_al_begin_io_prepare(struct drbd_device *device, struct drbd_interval *i)
+{
+	/* for bios crossing activity log extent boundaries,
+	 * we may need to activate two extents in one go */
+	unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
+	unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);
+	unsigned enr;
+	bool need_transaction = false;
+
+	D_ASSERT(device, first <= last);
+	D_ASSERT(device, atomic_read(&device->local_cnt) > 0);
+
+	for (enr = first; enr <= last; enr++) {
+		struct lc_element *al_ext;
+		wait_event(device->al_wait,
+				(al_ext = _al_get(device, enr, false)) != NULL);
+		if (al_ext->lc_number != enr)
+			need_transaction = true;
+	}
+	return need_transaction;
+}
+
+#if (PAGE_SHIFT + 3) < (AL_EXTENT_SHIFT - BM_BLOCK_SHIFT)
+/* Currently BM_BLOCK_SHIFT, BM_EXT_SHIFT and AL_EXTENT_SHIFT
+ * are still coupled, or assume too much about their relation.
+ * Code below will not work if this is violated.
+ * Will be cleaned up with some followup patch.
+ */
+# error FIXME
+#endif
+
+static unsigned int al_extent_to_bm_page(unsigned int al_enr)
+{
+	return al_enr >>
+		/* bit to page */
+		((PAGE_SHIFT + 3) -
+		/* al extent number to bit */
+		 (AL_EXTENT_SHIFT - BM_BLOCK_SHIFT));
+}
+
+static sector_t al_tr_number_to_on_disk_sector(struct drbd_device *device)
+{
+	const unsigned int stripes = device->ldev->md.al_stripes;
+	const unsigned int stripe_size_4kB = device->ldev->md.al_stripe_size_4k;
+
+	/* transaction number, modulo on-disk ring buffer wrap around */
+	unsigned int t = device->al_tr_number % (device->ldev->md.al_size_4k);
+
+	/* ... to aligned 4k on disk block */
+	t = ((t % stripes) * stripe_size_4kB) + t/stripes;
+
+	/* ... to 512 byte sector in activity log */
+	t *= 8;
+
+	/* ... plus offset to the on disk position */
+	return device->ldev->md.md_offset + device->ldev->md.al_offset + t;
+}
+
+static int __al_write_transaction(struct drbd_device *device, struct al_transaction_on_disk *buffer)
+{
+	struct lc_element *e;
+	sector_t sector;
+	int i, mx;
+	unsigned extent_nr;
+	unsigned crc = 0;
+	int err = 0;
+
+	memset(buffer, 0, sizeof(*buffer));
+	buffer->magic = cpu_to_be32(DRBD_AL_MAGIC);
+	buffer->tr_number = cpu_to_be32(device->al_tr_number);
+
+	i = 0;
+
+	drbd_bm_reset_al_hints(device);
+
+	/* Even though no one can start to change this list
+	 * once we set the LC_LOCKED -- from drbd_al_begin_io(),
+	 * lc_try_lock_for_transaction() --, someone may still
+	 * be in the process of changing it. */
+	spin_lock_irq(&device->al_lock);
+	list_for_each_entry(e, &device->act_log->to_be_changed, list) {
+		if (i == AL_UPDATES_PER_TRANSACTION) {
+			i++;
+			break;
+		}
+		buffer->update_slot_nr[i] = cpu_to_be16(e->lc_index);
+		buffer->update_extent_nr[i] = cpu_to_be32(e->lc_new_number);
+		if (e->lc_number != LC_FREE)
+			drbd_bm_mark_for_writeout(device,
+					al_extent_to_bm_page(e->lc_number));
+		i++;
+	}
+	spin_unlock_irq(&device->al_lock);
+	BUG_ON(i > AL_UPDATES_PER_TRANSACTION);
+
+	buffer->n_updates = cpu_to_be16(i);
+	for ( ; i < AL_UPDATES_PER_TRANSACTION; i++) {
+		buffer->update_slot_nr[i] = cpu_to_be16(-1);
+		buffer->update_extent_nr[i] = cpu_to_be32(LC_FREE);
+	}
+
+	buffer->context_size = cpu_to_be16(device->act_log->nr_elements);
+	buffer->context_start_slot_nr = cpu_to_be16(device->al_tr_cycle);
+
+	mx = min_t(int, AL_CONTEXT_PER_TRANSACTION,
+		   device->act_log->nr_elements - device->al_tr_cycle);
+	for (i = 0; i < mx; i++) {
+		unsigned idx = device->al_tr_cycle + i;
+		extent_nr = lc_element_by_index(device->act_log, idx)->lc_number;
+		buffer->context[i] = cpu_to_be32(extent_nr);
+	}
+	for (; i < AL_CONTEXT_PER_TRANSACTION; i++)
+		buffer->context[i] = cpu_to_be32(LC_FREE);
+
+	device->al_tr_cycle += AL_CONTEXT_PER_TRANSACTION;
+	if (device->al_tr_cycle >= device->act_log->nr_elements)
+		device->al_tr_cycle = 0;
+
+	sector = al_tr_number_to_on_disk_sector(device);
+
+	crc = crc32c(0, buffer, 4096);
+	buffer->crc32c = cpu_to_be32(crc);
+
+	if (drbd_bm_write_hinted(device))
+		err = -EIO;
+	else {
+		bool write_al_updates;
+		rcu_read_lock();
+		write_al_updates = rcu_dereference(device->ldev->disk_conf)->al_updates;
+		rcu_read_unlock();
+		if (write_al_updates) {
+			if (drbd_md_sync_page_io(device, device->ldev, sector, REQ_OP_WRITE)) {
+				err = -EIO;
+				drbd_chk_io_error(device, 1, DRBD_META_IO_ERROR);
+			} else {
+				device->al_tr_number++;
+				device->al_writ_cnt++;
+			}
+		}
+	}
+
+	return err;
+}
+
+static int al_write_transaction(struct drbd_device *device)
+{
+	struct al_transaction_on_disk *buffer;
+	int err;
+
+	if (!get_ldev(device)) {
+		drbd_err(device, "disk is %s, cannot start al transaction\n",
+			drbd_disk_str(device->state.disk));
+		return -EIO;
+	}
+
+	/* The bitmap write may have failed, causing a state change. */
+	if (device->state.disk < D_INCONSISTENT) {
+		drbd_err(device,
+			"disk is %s, cannot write al transaction\n",
+			drbd_disk_str(device->state.disk));
+		put_ldev(device);
+		return -EIO;
+	}
+
+	/* protects md_io_buffer, al_tr_cycle, ... */
+	buffer = drbd_md_get_buffer(device, __func__);
+	if (!buffer) {
+		drbd_err(device, "disk failed while waiting for md_io buffer\n");
+		put_ldev(device);
+		return -ENODEV;
+	}
+
+	err = __al_write_transaction(device, buffer);
+
+	drbd_md_put_buffer(device);
+	put_ldev(device);
+
+	return err;
+}
+
+
+void drbd_al_begin_io_commit(struct drbd_device *device)
+{
+	bool locked = false;
+
+	/* Serialize multiple transactions.
+	 * This uses test_and_set_bit, memory barrier is implicit.
+	 */
+	wait_event(device->al_wait,
+			device->act_log->pending_changes == 0 ||
+			(locked = lc_try_lock_for_transaction(device->act_log)));
+
+	if (locked) {
+		/* Double check: it may have been committed by someone else,
+		 * while we have been waiting for the lock. */
+		if (device->act_log->pending_changes) {
+			bool write_al_updates;
+
+			rcu_read_lock();
+			write_al_updates = rcu_dereference(device->ldev->disk_conf)->al_updates;
+			rcu_read_unlock();
+
+			if (write_al_updates)
+				al_write_transaction(device);
+			spin_lock_irq(&device->al_lock);
+			/* FIXME
+			if (err)
+				we need an "lc_cancel" here;
+			*/
+			lc_committed(device->act_log);
+			spin_unlock_irq(&device->al_lock);
+		}
+		lc_unlock(device->act_log);
+		wake_up(&device->al_wait);
+	}
+}
+
+/*
+ * @delegate:   delegate activity log I/O to the worker thread
+ */
+void drbd_al_begin_io(struct drbd_device *device, struct drbd_interval *i)
+{
+	if (drbd_al_begin_io_prepare(device, i))
+		drbd_al_begin_io_commit(device);
+}
+
+int drbd_al_begin_io_nonblock(struct drbd_device *device, struct drbd_interval *i)
+{
+	struct lru_cache *al = device->act_log;
+	/* for bios crossing activity log extent boundaries,
+	 * we may need to activate two extents in one go */
+	unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
+	unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);
+	unsigned nr_al_extents;
+	unsigned available_update_slots;
+	unsigned enr;
+
+	D_ASSERT(device, first <= last);
+
+	nr_al_extents = 1 + last - first; /* worst case: all touched extends are cold. */
+	available_update_slots = min(al->nr_elements - al->used,
+				al->max_pending_changes - al->pending_changes);
+
+	/* We want all necessary updates for a given request within the same transaction
+	 * We could first check how many updates are *actually* needed,
+	 * and use that instead of the worst-case nr_al_extents */
+	if (available_update_slots < nr_al_extents) {
+		/* Too many activity log extents are currently "hot".
+		 *
+		 * If we have accumulated pending changes already,
+		 * we made progress.
+		 *
+		 * If we cannot get even a single pending change through,
+		 * stop the fast path until we made some progress,
+		 * or requests to "cold" extents could be starved. */
+		if (!al->pending_changes)
+			__set_bit(__LC_STARVING, &device->act_log->flags);
+		return -ENOBUFS;
+	}
+
+	/* Is resync active in this area? */
+	for (enr = first; enr <= last; enr++) {
+		struct lc_element *tmp;
+		tmp = lc_find(device->resync, enr/AL_EXT_PER_BM_SECT);
+		if (unlikely(tmp != NULL)) {
+			struct bm_extent  *bm_ext = lc_entry(tmp, struct bm_extent, lce);
+			if (test_bit(BME_NO_WRITES, &bm_ext->flags)) {
+				if (!test_and_set_bit(BME_PRIORITY, &bm_ext->flags))
+					return -EBUSY;
+				return -EWOULDBLOCK;
+			}
+		}
+	}
+
+	/* Checkout the refcounts.
+	 * Given that we checked for available elements and update slots above,
+	 * this has to be successful. */
+	for (enr = first; enr <= last; enr++) {
+		struct lc_element *al_ext;
+		al_ext = lc_get_cumulative(device->act_log, enr);
+		if (!al_ext)
+			drbd_info(device, "LOGIC BUG for enr=%u\n", enr);
+	}
+	return 0;
+}
+
+void drbd_al_complete_io(struct drbd_device *device, struct drbd_interval *i)
+{
+	/* for bios crossing activity log extent boundaries,
+	 * we may need to activate two extents in one go */
+	unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
+	unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);
+	unsigned enr;
+	struct lc_element *extent;
+	unsigned long flags;
+
+	D_ASSERT(device, first <= last);
+	spin_lock_irqsave(&device->al_lock, flags);
+
+	for (enr = first; enr <= last; enr++) {
+		extent = lc_find(device->act_log, enr);
+		if (!extent) {
+			drbd_err(device, "al_complete_io() called on inactive extent %u\n", enr);
+			continue;
+		}
+		lc_put(device->act_log, extent);
+	}
+	spin_unlock_irqrestore(&device->al_lock, flags);
+	wake_up(&device->al_wait);
+}
+
+static int _try_lc_del(struct drbd_device *device, struct lc_element *al_ext)
+{
+	int rv;
+
+	spin_lock_irq(&device->al_lock);
+	rv = (al_ext->refcnt == 0);
+	if (likely(rv))
+		lc_del(device->act_log, al_ext);
+	spin_unlock_irq(&device->al_lock);
+
+	return rv;
+}
+
+/**
+ * drbd_al_shrink() - Removes all active extents form the activity log
+ * @device:	DRBD device.
+ *
+ * Removes all active extents form the activity log, waiting until
+ * the reference count of each entry dropped to 0 first, of course.
+ *
+ * You need to lock device->act_log with lc_try_lock() / lc_unlock()
+ */
+void drbd_al_shrink(struct drbd_device *device)
+{
+	struct lc_element *al_ext;
+	int i;
+
+	D_ASSERT(device, test_bit(__LC_LOCKED, &device->act_log->flags));
+
+	for (i = 0; i < device->act_log->nr_elements; i++) {
+		al_ext = lc_element_by_index(device->act_log, i);
+		if (al_ext->lc_number == LC_FREE)
+			continue;
+		wait_event(device->al_wait, _try_lc_del(device, al_ext));
+	}
+
+	wake_up(&device->al_wait);
+}
+
+int drbd_al_initialize(struct drbd_device *device, void *buffer)
+{
+	struct al_transaction_on_disk *al = buffer;
+	struct drbd_md *md = &device->ldev->md;
+	int al_size_4k = md->al_stripes * md->al_stripe_size_4k;
+	int i;
+
+	__al_write_transaction(device, al);
+	/* There may or may not have been a pending transaction. */
+	spin_lock_irq(&device->al_lock);
+	lc_committed(device->act_log);
+	spin_unlock_irq(&device->al_lock);
+
+	/* The rest of the transactions will have an empty "updates" list, and
+	 * are written out only to provide the context, and to initialize the
+	 * on-disk ring buffer. */
+	for (i = 1; i < al_size_4k; i++) {
+		int err = __al_write_transaction(device, al);
+		if (err)
+			return err;
+	}
+	return 0;
+}
+
+static const char *drbd_change_sync_fname[] = {
+	[RECORD_RS_FAILED] = "drbd_rs_failed_io",
+	[SET_IN_SYNC] = "drbd_set_in_sync",
+	[SET_OUT_OF_SYNC] = "drbd_set_out_of_sync"
+};
+
+/* ATTENTION. The AL's extents are 4MB each, while the extents in the
+ * resync LRU-cache are 16MB each.
+ * The caller of this function has to hold an get_ldev() reference.
+ *
+ * Adjusts the caching members ->rs_left (success) or ->rs_failed (!success),
+ * potentially pulling in (and recounting the corresponding bits)
+ * this resync extent into the resync extent lru cache.
+ *
+ * Returns whether all bits have been cleared for this resync extent,
+ * precisely: (rs_left <= rs_failed)
+ *
+ * TODO will be obsoleted once we have a caching lru of the on disk bitmap
+ */
+static bool update_rs_extent(struct drbd_device *device,
+		unsigned int enr, int count,
+		enum update_sync_bits_mode mode)
+{
+	struct lc_element *e;
+
+	D_ASSERT(device, atomic_read(&device->local_cnt));
+
+	/* When setting out-of-sync bits,
+	 * we don't need it cached (lc_find).
+	 * But if it is present in the cache,
+	 * we should update the cached bit count.
+	 * Otherwise, that extent should be in the resync extent lru cache
+	 * already -- or we want to pull it in if necessary -- (lc_get),
+	 * then update and check rs_left and rs_failed. */
+	if (mode == SET_OUT_OF_SYNC)
+		e = lc_find(device->resync, enr);
+	else
+		e = lc_get(device->resync, enr);
+	if (e) {
+		struct bm_extent *ext = lc_entry(e, struct bm_extent, lce);
+		if (ext->lce.lc_number == enr) {
+			if (mode == SET_IN_SYNC)
+				ext->rs_left -= count;
+			else if (mode == SET_OUT_OF_SYNC)
+				ext->rs_left += count;
+			else
+				ext->rs_failed += count;
+			if (ext->rs_left < ext->rs_failed) {
+				drbd_warn(device, "BAD! enr=%u rs_left=%d "
+				    "rs_failed=%d count=%d cstate=%s\n",
+				     ext->lce.lc_number, ext->rs_left,
+				     ext->rs_failed, count,
+				     drbd_conn_str(device->state.conn));
+
+				/* We don't expect to be able to clear more bits
+				 * than have been set when we originally counted
+				 * the set bits to cache that value in ext->rs_left.
+				 * Whatever the reason (disconnect during resync,
+				 * delayed local completion of an application write),
+				 * try to fix it up by recounting here. */
+				ext->rs_left = drbd_bm_e_weight(device, enr);
+			}
+		} else {
+			/* Normally this element should be in the cache,
+			 * since drbd_rs_begin_io() pulled it already in.
+			 *
+			 * But maybe an application write finished, and we set
+			 * something outside the resync lru_cache in sync.
+			 */
+			int rs_left = drbd_bm_e_weight(device, enr);
+			if (ext->flags != 0) {
+				drbd_warn(device, "changing resync lce: %d[%u;%02lx]"
+				     " -> %d[%u;00]\n",
+				     ext->lce.lc_number, ext->rs_left,
+				     ext->flags, enr, rs_left);
+				ext->flags = 0;
+			}
+			if (ext->rs_failed) {
+				drbd_warn(device, "Kicking resync_lru element enr=%u "
+				     "out with rs_failed=%d\n",
+				     ext->lce.lc_number, ext->rs_failed);
+			}
+			ext->rs_left = rs_left;
+			ext->rs_failed = (mode == RECORD_RS_FAILED) ? count : 0;
+			/* we don't keep a persistent log of the resync lru,
+			 * we can commit any change right away. */
+			lc_committed(device->resync);
+		}
+		if (mode != SET_OUT_OF_SYNC)
+			lc_put(device->resync, &ext->lce);
+		/* no race, we are within the al_lock! */
+
+		if (ext->rs_left <= ext->rs_failed) {
+			ext->rs_failed = 0;
+			return true;
+		}
+	} else if (mode != SET_OUT_OF_SYNC) {
+		/* be quiet if lc_find() did not find it. */
+		drbd_err(device, "lc_get() failed! locked=%d/%d flags=%lu\n",
+		    device->resync_locked,
+		    device->resync->nr_elements,
+		    device->resync->flags);
+	}
+	return false;
+}
+
+void drbd_advance_rs_marks(struct drbd_peer_device *peer_device, unsigned long still_to_go)
+{
+	struct drbd_device *device = peer_device->device;
+	unsigned long now = jiffies;
+	unsigned long last = device->rs_mark_time[device->rs_last_mark];
+	int next = (device->rs_last_mark + 1) % DRBD_SYNC_MARKS;
+	if (time_after_eq(now, last + DRBD_SYNC_MARK_STEP)) {
+		if (device->rs_mark_left[device->rs_last_mark] != still_to_go &&
+		    device->state.conn != C_PAUSED_SYNC_T &&
+		    device->state.conn != C_PAUSED_SYNC_S) {
+			device->rs_mark_time[next] = now;
+			device->rs_mark_left[next] = still_to_go;
+			device->rs_last_mark = next;
+		}
+	}
+}
+
+/* It is called lazy update, so don't do write-out too often. */
+static bool lazy_bitmap_update_due(struct drbd_device *device)
+{
+	return time_after(jiffies, device->rs_last_bcast + 2*HZ);
+}
+
+static void maybe_schedule_on_disk_bitmap_update(struct drbd_device *device, bool rs_done)
+{
+	if (rs_done) {
+		struct drbd_connection *connection = first_peer_device(device)->connection;
+		if (connection->agreed_pro_version <= 95 ||
+		    is_sync_target_state(device->state.conn))
+			set_bit(RS_DONE, &device->flags);
+			/* and also set RS_PROGRESS below */
+
+		/* Else: rather wait for explicit notification via receive_state,
+		 * to avoid uuids-rotated-too-fast causing full resync
+		 * in next handshake, in case the replication link breaks
+		 * at the most unfortunate time... */
+	} else if (!lazy_bitmap_update_due(device))
+		return;
+
+	drbd_device_post_work(device, RS_PROGRESS);
+}
+
+static int update_sync_bits(struct drbd_device *device,
+		unsigned long sbnr, unsigned long ebnr,
+		enum update_sync_bits_mode mode)
+{
+	/*
+	 * We keep a count of set bits per resync-extent in the ->rs_left
+	 * caching member, so we need to loop and work within the resync extent
+	 * alignment. Typically this loop will execute exactly once.
+	 */
+	unsigned long flags;
+	unsigned long count = 0;
+	unsigned int cleared = 0;
+	while (sbnr <= ebnr) {
+		/* set temporary boundary bit number to last bit number within
+		 * the resync extent of the current start bit number,
+		 * but cap at provided end bit number */
+		unsigned long tbnr = min(ebnr, sbnr | BM_BLOCKS_PER_BM_EXT_MASK);
+		unsigned long c;
+
+		if (mode == RECORD_RS_FAILED)
+			/* Only called from drbd_rs_failed_io(), bits
+			 * supposedly still set.  Recount, maybe some
+			 * of the bits have been successfully cleared
+			 * by application IO meanwhile.
+			 */
+			c = drbd_bm_count_bits(device, sbnr, tbnr);
+		else if (mode == SET_IN_SYNC)
+			c = drbd_bm_clear_bits(device, sbnr, tbnr);
+		else /* if (mode == SET_OUT_OF_SYNC) */
+			c = drbd_bm_set_bits(device, sbnr, tbnr);
+
+		if (c) {
+			spin_lock_irqsave(&device->al_lock, flags);
+			cleared += update_rs_extent(device, BM_BIT_TO_EXT(sbnr), c, mode);
+			spin_unlock_irqrestore(&device->al_lock, flags);
+			count += c;
+		}
+		sbnr = tbnr + 1;
+	}
+	if (count) {
+		if (mode == SET_IN_SYNC) {
+			unsigned long still_to_go = drbd_bm_total_weight(device);
+			bool rs_is_done = (still_to_go <= device->rs_failed);
+			drbd_advance_rs_marks(first_peer_device(device), still_to_go);
+			if (cleared || rs_is_done)
+				maybe_schedule_on_disk_bitmap_update(device, rs_is_done);
+		} else if (mode == RECORD_RS_FAILED)
+			device->rs_failed += count;
+		wake_up(&device->al_wait);
+	}
+	return count;
+}
+
+static bool plausible_request_size(int size)
+{
+	return size > 0
+		&& size <= DRBD_MAX_BATCH_BIO_SIZE
+		&& IS_ALIGNED(size, 512);
+}
+
+/* clear the bit corresponding to the piece of storage in question:
+ * size byte of data starting from sector.  Only clear a bits of the affected
+ * one ore more _aligned_ BM_BLOCK_SIZE blocks.
+ *
+ * called by worker on C_SYNC_TARGET and receiver on SyncSource.
+ *
+ */
+int __drbd_change_sync(struct drbd_peer_device *peer_device, sector_t sector, int size,
+		enum update_sync_bits_mode mode)
+{
+	/* Is called from worker and receiver context _only_ */
+	struct drbd_device *device = peer_device->device;
+	unsigned long sbnr, ebnr, lbnr;
+	unsigned long count = 0;
+	sector_t esector, nr_sectors;
+
+	/* This would be an empty REQ_PREFLUSH, be silent. */
+	if ((mode == SET_OUT_OF_SYNC) && size == 0)
+		return 0;
+
+	if (!plausible_request_size(size)) {
+		drbd_err(device, "%s: sector=%llus size=%d nonsense!\n",
+				drbd_change_sync_fname[mode],
+				(unsigned long long)sector, size);
+		return 0;
+	}
+
+	if (!get_ldev(device))
+		return 0; /* no disk, no metadata, no bitmap to manipulate bits in */
+
+	nr_sectors = get_capacity(device->vdisk);
+	esector = sector + (size >> 9) - 1;
+
+	if (!expect(device, sector < nr_sectors))
+		goto out;
+	if (!expect(device, esector < nr_sectors))
+		esector = nr_sectors - 1;
+
+	lbnr = BM_SECT_TO_BIT(nr_sectors-1);
+
+	if (mode == SET_IN_SYNC) {
+		/* Round up start sector, round down end sector.  We make sure
+		 * we only clear full, aligned, BM_BLOCK_SIZE blocks. */
+		if (unlikely(esector < BM_SECT_PER_BIT-1))
+			goto out;
+		if (unlikely(esector == (nr_sectors-1)))
+			ebnr = lbnr;
+		else
+			ebnr = BM_SECT_TO_BIT(esector - (BM_SECT_PER_BIT-1));
+		sbnr = BM_SECT_TO_BIT(sector + BM_SECT_PER_BIT-1);
+	} else {
+		/* We set it out of sync, or record resync failure.
+		 * Should not round anything here. */
+		sbnr = BM_SECT_TO_BIT(sector);
+		ebnr = BM_SECT_TO_BIT(esector);
+	}
+
+	count = update_sync_bits(device, sbnr, ebnr, mode);
+out:
+	put_ldev(device);
+	return count;
+}
+
+static
+struct bm_extent *_bme_get(struct drbd_device *device, unsigned int enr)
+{
+	struct lc_element *e;
+	struct bm_extent *bm_ext;
+	int wakeup = 0;
+	unsigned long rs_flags;
+
+	spin_lock_irq(&device->al_lock);
+	if (device->resync_locked > device->resync->nr_elements/2) {
+		spin_unlock_irq(&device->al_lock);
+		return NULL;
+	}
+	e = lc_get(device->resync, enr);
+	bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
+	if (bm_ext) {
+		if (bm_ext->lce.lc_number != enr) {
+			bm_ext->rs_left = drbd_bm_e_weight(device, enr);
+			bm_ext->rs_failed = 0;
+			lc_committed(device->resync);
+			wakeup = 1;
+		}
+		if (bm_ext->lce.refcnt == 1)
+			device->resync_locked++;
+		set_bit(BME_NO_WRITES, &bm_ext->flags);
+	}
+	rs_flags = device->resync->flags;
+	spin_unlock_irq(&device->al_lock);
+	if (wakeup)
+		wake_up(&device->al_wait);
+
+	if (!bm_ext) {
+		if (rs_flags & LC_STARVING)
+			drbd_warn(device, "Have to wait for element"
+			     " (resync LRU too small?)\n");
+		BUG_ON(rs_flags & LC_LOCKED);
+	}
+
+	return bm_ext;
+}
+
+static int _is_in_al(struct drbd_device *device, unsigned int enr)
+{
+	int rv;
+
+	spin_lock_irq(&device->al_lock);
+	rv = lc_is_used(device->act_log, enr);
+	spin_unlock_irq(&device->al_lock);
+
+	return rv;
+}
+
+/**
+ * drbd_rs_begin_io() - Gets an extent in the resync LRU cache and sets it to BME_LOCKED
+ * @device:	DRBD device.
+ * @sector:	The sector number.
+ *
+ * This functions sleeps on al_wait. Returns 0 on success, -EINTR if interrupted.
+ */
+int drbd_rs_begin_io(struct drbd_device *device, sector_t sector)
+{
+	unsigned int enr = BM_SECT_TO_EXT(sector);
+	struct bm_extent *bm_ext;
+	int i, sig;
+	bool sa;
+
+retry:
+	sig = wait_event_interruptible(device->al_wait,
+			(bm_ext = _bme_get(device, enr)));
+	if (sig)
+		return -EINTR;
+
+	if (test_bit(BME_LOCKED, &bm_ext->flags))
+		return 0;
+
+	/* step aside only while we are above c-min-rate; unless disabled. */
+	sa = drbd_rs_c_min_rate_throttle(device);
+
+	for (i = 0; i < AL_EXT_PER_BM_SECT; i++) {
+		sig = wait_event_interruptible(device->al_wait,
+					       !_is_in_al(device, enr * AL_EXT_PER_BM_SECT + i) ||
+					       (sa && test_bit(BME_PRIORITY, &bm_ext->flags)));
+
+		if (sig || (sa && test_bit(BME_PRIORITY, &bm_ext->flags))) {
+			spin_lock_irq(&device->al_lock);
+			if (lc_put(device->resync, &bm_ext->lce) == 0) {
+				bm_ext->flags = 0; /* clears BME_NO_WRITES and eventually BME_PRIORITY */
+				device->resync_locked--;
+				wake_up(&device->al_wait);
+			}
+			spin_unlock_irq(&device->al_lock);
+			if (sig)
+				return -EINTR;
+			if (schedule_timeout_interruptible(HZ/10))
+				return -EINTR;
+			goto retry;
+		}
+	}
+	set_bit(BME_LOCKED, &bm_ext->flags);
+	return 0;
+}
+
+/**
+ * drbd_try_rs_begin_io() - Gets an extent in the resync LRU cache, does not sleep
+ * @device:	DRBD device.
+ * @sector:	The sector number.
+ *
+ * Gets an extent in the resync LRU cache, sets it to BME_NO_WRITES, then
+ * tries to set it to BME_LOCKED. Returns 0 upon success, and -EAGAIN
+ * if there is still application IO going on in this area.
+ */
+int drbd_try_rs_begin_io(struct drbd_peer_device *peer_device, sector_t sector)
+{
+	struct drbd_device *device = peer_device->device;
+	unsigned int enr = BM_SECT_TO_EXT(sector);
+	const unsigned int al_enr = enr*AL_EXT_PER_BM_SECT;
+	struct lc_element *e;
+	struct bm_extent *bm_ext;
+	int i;
+	bool throttle = drbd_rs_should_slow_down(peer_device, sector, true);
+
+	/* If we need to throttle, a half-locked (only marked BME_NO_WRITES,
+	 * not yet BME_LOCKED) extent needs to be kicked out explicitly if we
+	 * need to throttle. There is at most one such half-locked extent,
+	 * which is remembered in resync_wenr. */
+
+	if (throttle && device->resync_wenr != enr)
+		return -EAGAIN;
+
+	spin_lock_irq(&device->al_lock);
+	if (device->resync_wenr != LC_FREE && device->resync_wenr != enr) {
+		/* in case you have very heavy scattered io, it may
+		 * stall the syncer undefined if we give up the ref count
+		 * when we try again and requeue.
+		 *
+		 * if we don't give up the refcount, but the next time
+		 * we are scheduled this extent has been "synced" by new
+		 * application writes, we'd miss the lc_put on the
+		 * extent we keep the refcount on.
+		 * so we remembered which extent we had to try again, and
+		 * if the next requested one is something else, we do
+		 * the lc_put here...
+		 * we also have to wake_up
+		 */
+		e = lc_find(device->resync, device->resync_wenr);
+		bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
+		if (bm_ext) {
+			D_ASSERT(device, !test_bit(BME_LOCKED, &bm_ext->flags));
+			D_ASSERT(device, test_bit(BME_NO_WRITES, &bm_ext->flags));
+			clear_bit(BME_NO_WRITES, &bm_ext->flags);
+			device->resync_wenr = LC_FREE;
+			if (lc_put(device->resync, &bm_ext->lce) == 0) {
+				bm_ext->flags = 0;
+				device->resync_locked--;
+			}
+			wake_up(&device->al_wait);
+		} else {
+			drbd_alert(device, "LOGIC BUG\n");
+		}
+	}
+	/* TRY. */
+	e = lc_try_get(device->resync, enr);
+	bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
+	if (bm_ext) {
+		if (test_bit(BME_LOCKED, &bm_ext->flags))
+			goto proceed;
+		if (!test_and_set_bit(BME_NO_WRITES, &bm_ext->flags)) {
+			device->resync_locked++;
+		} else {
+			/* we did set the BME_NO_WRITES,
+			 * but then could not set BME_LOCKED,
+			 * so we tried again.
+			 * drop the extra reference. */
+			bm_ext->lce.refcnt--;
+			D_ASSERT(device, bm_ext->lce.refcnt > 0);
+		}
+		goto check_al;
+	} else {
+		/* do we rather want to try later? */
+		if (device->resync_locked > device->resync->nr_elements-3)
+			goto try_again;
+		/* Do or do not. There is no try. -- Yoda */
+		e = lc_get(device->resync, enr);
+		bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
+		if (!bm_ext) {
+			const unsigned long rs_flags = device->resync->flags;
+			if (rs_flags & LC_STARVING)
+				drbd_warn(device, "Have to wait for element"
+				     " (resync LRU too small?)\n");
+			BUG_ON(rs_flags & LC_LOCKED);
+			goto try_again;
+		}
+		if (bm_ext->lce.lc_number != enr) {
+			bm_ext->rs_left = drbd_bm_e_weight(device, enr);
+			bm_ext->rs_failed = 0;
+			lc_committed(device->resync);
+			wake_up(&device->al_wait);
+			D_ASSERT(device, test_bit(BME_LOCKED, &bm_ext->flags) == 0);
+		}
+		set_bit(BME_NO_WRITES, &bm_ext->flags);
+		D_ASSERT(device, bm_ext->lce.refcnt == 1);
+		device->resync_locked++;
+		goto check_al;
+	}
+check_al:
+	for (i = 0; i < AL_EXT_PER_BM_SECT; i++) {
+		if (lc_is_used(device->act_log, al_enr+i))
+			goto try_again;
+	}
+	set_bit(BME_LOCKED, &bm_ext->flags);
+proceed:
+	device->resync_wenr = LC_FREE;
+	spin_unlock_irq(&device->al_lock);
+	return 0;
+
+try_again:
+	if (bm_ext) {
+		if (throttle) {
+			D_ASSERT(device, !test_bit(BME_LOCKED, &bm_ext->flags));
+			D_ASSERT(device, test_bit(BME_NO_WRITES, &bm_ext->flags));
+			clear_bit(BME_NO_WRITES, &bm_ext->flags);
+			device->resync_wenr = LC_FREE;
+			if (lc_put(device->resync, &bm_ext->lce) == 0) {
+				bm_ext->flags = 0;
+				device->resync_locked--;
+			}
+			wake_up(&device->al_wait);
+		} else
+			device->resync_wenr = enr;
+	}
+	spin_unlock_irq(&device->al_lock);
+	return -EAGAIN;
+}
+
+void drbd_rs_complete_io(struct drbd_device *device, sector_t sector)
+{
+	unsigned int enr = BM_SECT_TO_EXT(sector);
+	struct lc_element *e;
+	struct bm_extent *bm_ext;
+	unsigned long flags;
+
+	spin_lock_irqsave(&device->al_lock, flags);
+	e = lc_find(device->resync, enr);
+	bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
+	if (!bm_ext) {
+		spin_unlock_irqrestore(&device->al_lock, flags);
+		if (drbd_ratelimit())
+			drbd_err(device, "drbd_rs_complete_io() called, but extent not found\n");
+		return;
+	}
+
+	if (bm_ext->lce.refcnt == 0) {
+		spin_unlock_irqrestore(&device->al_lock, flags);
+		drbd_err(device, "drbd_rs_complete_io(,%llu [=%u]) called, "
+		    "but refcnt is 0!?\n",
+		    (unsigned long long)sector, enr);
+		return;
+	}
+
+	if (lc_put(device->resync, &bm_ext->lce) == 0) {
+		bm_ext->flags = 0; /* clear BME_LOCKED, BME_NO_WRITES and BME_PRIORITY */
+		device->resync_locked--;
+		wake_up(&device->al_wait);
+	}
+
+	spin_unlock_irqrestore(&device->al_lock, flags);
+}
+
+/**
+ * drbd_rs_cancel_all() - Removes all extents from the resync LRU (even BME_LOCKED)
+ * @device:	DRBD device.
+ */
+void drbd_rs_cancel_all(struct drbd_device *device)
+{
+	spin_lock_irq(&device->al_lock);
+
+	if (get_ldev_if_state(device, D_FAILED)) { /* Makes sure ->resync is there. */
+		lc_reset(device->resync);
+		put_ldev(device);
+	}
+	device->resync_locked = 0;
+	device->resync_wenr = LC_FREE;
+	spin_unlock_irq(&device->al_lock);
+	wake_up(&device->al_wait);
+}
+
+/**
+ * drbd_rs_del_all() - Gracefully remove all extents from the resync LRU
+ * @device:	DRBD device.
+ *
+ * Returns 0 upon success, -EAGAIN if at least one reference count was
+ * not zero.
+ */
+int drbd_rs_del_all(struct drbd_device *device)
+{
+	struct lc_element *e;
+	struct bm_extent *bm_ext;
+	int i;
+
+	spin_lock_irq(&device->al_lock);
+
+	if (get_ldev_if_state(device, D_FAILED)) {
+		/* ok, ->resync is there. */
+		for (i = 0; i < device->resync->nr_elements; i++) {
+			e = lc_element_by_index(device->resync, i);
+			bm_ext = lc_entry(e, struct bm_extent, lce);
+			if (bm_ext->lce.lc_number == LC_FREE)
+				continue;
+			if (bm_ext->lce.lc_number == device->resync_wenr) {
+				drbd_info(device, "dropping %u in drbd_rs_del_all, apparently"
+				     " got 'synced' by application io\n",
+				     device->resync_wenr);
+				D_ASSERT(device, !test_bit(BME_LOCKED, &bm_ext->flags));
+				D_ASSERT(device, test_bit(BME_NO_WRITES, &bm_ext->flags));
+				clear_bit(BME_NO_WRITES, &bm_ext->flags);
+				device->resync_wenr = LC_FREE;
+				lc_put(device->resync, &bm_ext->lce);
+			}
+			if (bm_ext->lce.refcnt != 0) {
+				drbd_info(device, "Retrying drbd_rs_del_all() later. "
+				     "refcnt=%d\n", bm_ext->lce.refcnt);
+				put_ldev(device);
+				spin_unlock_irq(&device->al_lock);
+				return -EAGAIN;
+			}
+			D_ASSERT(device, !test_bit(BME_LOCKED, &bm_ext->flags));
+			D_ASSERT(device, !test_bit(BME_NO_WRITES, &bm_ext->flags));
+			lc_del(device->resync, &bm_ext->lce);
+		}
+		D_ASSERT(device, device->resync->used == 0);
+		put_ldev(device);
+	}
+	spin_unlock_irq(&device->al_lock);
+	wake_up(&device->al_wait);
+
+	return 0;
+}