[PATCH 03/16] drbd: tracking of active extents

[Philipp Reisner]

Within DRBD the activity log is used to track extents (4MB each) in which IO
happens (or happened recently). It is based on the LRU cache. Each change of
the activity log causes a meta data update (single sector write).  The size
of the activity log is configured by the user, and is a tradeoff between
minimizing updates to the meta data and the resync time after the crash of a
primary node.

Signed-off-by: Philipp Reisner <philipp.reisner@xxxxxxxxxx>
Signed-off-by: Lars Ellenberg <lars.ellenberg@xxxxxxxxxx>

---
diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c
new file mode 100644
index 0000000..1e53d16
--- /dev/null
+++ b/drivers/block/drbd/drbd_actlog.c
@@ -0,0 +1,1485 @@
+/*
+   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@xxxxxxxxxx>.
+   Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@xxxxxxxxxx>.
+
+   drbd is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   drbd is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with drbd; see the file COPYING.  If not, write to
+   the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
+
+ */
+
+#include <linux/slab.h>
+#include <linux/drbd.h>
+#include "drbd_int.h"
+#include "drbd_tracing.h"
+#include "drbd_wrappers.h"
+
+/* We maintain a trivial check sum in our on disk activity log.
+ * With that we can ensure correct operation even when the storage
+ * device might do a partial (last) sector write while loosing power.
+ */
+struct __packed al_transaction {
+	u32       magic;
+	u32       tr_number;
+	struct __packed {
+		u32 pos;
+		u32 extent; } updates[1 + AL_EXTENTS_PT];
+	u32       xor_sum;
+};
+
+struct update_odbm_work {
+	struct drbd_work w;
+	unsigned int enr;
+};
+
+struct update_al_work {
+	struct drbd_work w;
+	struct lc_element *al_ext;
+	struct completion event;
+	unsigned int enr;
+	/* if old_enr != LC_FREE, write corresponding bitmap sector, too */
+	unsigned int old_enr;
+};
+
+struct drbd_atodb_wait {
+	atomic_t           count;
+	struct completion  io_done;
+	struct drbd_conf   *mdev;
+	int                error;
+};
+
+
+int w_al_write_transaction(struct drbd_conf *, struct drbd_work *, int);
+
+/* The actual tracepoint needs to have constant number of known arguments...
+ */
+void trace_drbd_resync(struct drbd_conf *mdev, int level, const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	trace__drbd_resync(mdev, level, fmt, ap);
+	va_end(ap);
+}
+
+static int _drbd_md_sync_page_io(struct drbd_conf *mdev,
+				 struct drbd_backing_dev *bdev,
+				 struct page *page, sector_t sector,
+				 int rw, int size)
+{
+	struct bio *bio;
+	struct drbd_md_io md_io;
+	int ok;
+
+	md_io.mdev = mdev;
+	init_completion(&md_io.event);
+	md_io.error = 0;
+
+	if (rw == WRITE && !test_bit(MD_NO_BARRIER, &mdev->flags))
+		rw |= (1<<BIO_RW_BARRIER);
+	rw |= ((1<<BIO_RW_UNPLUG) | (1<<BIO_RW_SYNCIO));
+
+ retry:
+	bio = bio_alloc(GFP_NOIO, 1);
+	bio->bi_bdev = bdev->md_bdev;
+	bio->bi_sector = sector;
+	ok = (bio_add_page(bio, page, size, 0) == size);
+	if (!ok)
+		goto out;
+	bio->bi_private = &md_io;
+	bio->bi_end_io = drbd_md_io_complete;
+	bio->bi_rw = rw;
+
+	trace_drbd_bio(mdev, "Md", bio, 0, NULL);
+
+	if (FAULT_ACTIVE(mdev, (rw & WRITE) ? DRBD_FAULT_MD_WR : DRBD_FAULT_MD_RD))
+		bio_endio(bio, -EIO);
+	else
+		submit_bio(rw, bio);
+	wait_for_completion(&md_io.event);
+	ok = bio_flagged(bio, BIO_UPTODATE) && md_io.error == 0;
+
+	/* check for unsupported barrier op.
+	 * would rather check on EOPNOTSUPP, but that is not reliable.
+	 * don't try again for ANY return value != 0 */
+	if (unlikely(bio_barrier(bio) && !ok)) {
+		/* Try again with no barrier */
+		dev_warn(DEV, "Barriers not supported on meta data device - disabling\n");
+		set_bit(MD_NO_BARRIER, &mdev->flags);
+		rw &= ~(1 << BIO_RW_BARRIER);
+		bio_put(bio);
+		goto retry;
+	}
+ out:
+	bio_put(bio);
+	return ok;
+}
+
+int drbd_md_sync_page_io(struct drbd_conf *mdev, struct drbd_backing_dev *bdev,
+			 sector_t sector, int rw)
+{
+	int logical_block_size, mask, ok;
+	int offset = 0;
+	struct page *iop = mdev->md_io_page;
+
+	D_ASSERT(mutex_is_locked(&mdev->md_io_mutex));
+
+	BUG_ON(!bdev->md_bdev);
+
+	logical_block_size = bdev_logical_block_size(bdev->md_bdev);
+	if (logical_block_size == 0)
+		logical_block_size = MD_SECTOR_SIZE;
+
+	/* in case logical_block_size != 512 [ s390 only? ] */
+	if (logical_block_size != MD_SECTOR_SIZE) {
+		mask = (logical_block_size / MD_SECTOR_SIZE) - 1;
+		D_ASSERT(mask == 1 || mask == 3 || mask == 7);
+		D_ASSERT(logical_block_size == (mask+1) * MD_SECTOR_SIZE);
+		offset = sector & mask;
+		sector = sector & ~mask;
+		iop = mdev->md_io_tmpp;
+
+		if (rw & WRITE) {
+			/* these are GFP_KERNEL pages, preallocated
+			 * on device initialization */
+			void *p = page_address(mdev->md_io_page);
+			void *hp = page_address(mdev->md_io_tmpp);
+
+			ok = _drbd_md_sync_page_io(mdev, bdev, iop, sector,
+					READ, logical_block_size);
+
+			if (unlikely(!ok)) {
+				dev_err(DEV, "drbd_md_sync_page_io(,%llus,"
+				    "READ [logical_block_size!=512]) failed!\n",
+				    (unsigned long long)sector);
+				return 0;
+			}
+
+			memcpy(hp + offset*MD_SECTOR_SIZE, p, MD_SECTOR_SIZE);
+		}
+	}
+
+	if (sector < drbd_md_first_sector(bdev) ||
+	    sector > drbd_md_last_sector(bdev))
+		dev_alert(DEV, "%s [%d]:%s(,%llus,%s) out of range md access!\n",
+		     current->comm, current->pid, __func__,
+		     (unsigned long long)sector, (rw & WRITE) ? "WRITE" : "READ");
+
+	ok = _drbd_md_sync_page_io(mdev, bdev, iop, sector, rw, logical_block_size);
+	if (unlikely(!ok)) {
+		dev_err(DEV, "drbd_md_sync_page_io(,%llus,%s) failed!\n",
+		    (unsigned long long)sector, (rw & WRITE) ? "WRITE" : "READ");
+		return 0;
+	}
+
+	if (logical_block_size != MD_SECTOR_SIZE && !(rw & WRITE)) {
+		void *p = page_address(mdev->md_io_page);
+		void *hp = page_address(mdev->md_io_tmpp);
+
+		memcpy(p, hp + offset*MD_SECTOR_SIZE, MD_SECTOR_SIZE);
+	}
+
+	return ok;
+}
+
+static struct lc_element *_al_get(struct drbd_conf *mdev, unsigned int enr)
+{
+	struct lc_element *al_ext;
+	struct lc_element *tmp;
+	unsigned long     al_flags = 0;
+
+	spin_lock_irq(&mdev->al_lock);
+	tmp = lc_find(mdev->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)) {
+			spin_unlock_irq(&mdev->al_lock);
+			return NULL;
+		}
+	}
+	al_ext   = lc_get(mdev->act_log, enr);
+	al_flags = mdev->act_log->flags;
+	spin_unlock_irq(&mdev->al_lock);
+
+	/*
+	if (!al_ext) {
+		if (al_flags & LC_STARVING)
+			dev_warn(DEV, "Have to wait for LRU element (AL too small?)\n");
+		if (al_flags & LC_DIRTY)
+			dev_warn(DEV, "Ongoing AL update (AL device too slow?)\n");
+	}
+	*/
+
+	return al_ext;
+}
+
+void drbd_al_begin_io(struct drbd_conf *mdev, sector_t sector)
+{
+	unsigned int enr = (sector >> (AL_EXTENT_SHIFT-9));
+	struct lc_element *al_ext;
+	struct update_al_work al_work;
+
+	D_ASSERT(atomic_read(&mdev->local_cnt) > 0);
+
+	trace_drbd_actlog(mdev, sector, "al_begin_io");
+
+	wait_event(mdev->al_wait, (al_ext = _al_get(mdev, enr)));
+
+	if (al_ext->lc_number != enr) {
+		/* drbd_al_write_transaction(mdev,al_ext,enr);
+		 * recurses into generic_make_request(), which
+		 * disalows recursion, bios being serialized on the
+		 * current->bio_tail list now.
+		 * we have to delegate updates to the activity log
+		 * to the worker thread. */
+		init_completion(&al_work.event);
+		al_work.al_ext = al_ext;
+		al_work.enr = enr;
+		al_work.old_enr = al_ext->lc_number;
+		al_work.w.cb = w_al_write_transaction;
+		drbd_queue_work_front(&mdev->data.work, &al_work.w);
+		wait_for_completion(&al_work.event);
+
+		mdev->al_writ_cnt++;
+
+		spin_lock_irq(&mdev->al_lock);
+		lc_changed(mdev->act_log, al_ext);
+		spin_unlock_irq(&mdev->al_lock);
+		wake_up(&mdev->al_wait);
+	}
+}
+
+void drbd_al_complete_io(struct drbd_conf *mdev, sector_t sector)
+{
+	unsigned int enr = (sector >> (AL_EXTENT_SHIFT-9));
+	struct lc_element *extent;
+	unsigned long flags;
+
+	trace_drbd_actlog(mdev, sector, "al_complete_io");
+
+	spin_lock_irqsave(&mdev->al_lock, flags);
+
+	extent = lc_find(mdev->act_log, enr);
+
+	if (!extent) {
+		spin_unlock_irqrestore(&mdev->al_lock, flags);
+		dev_err(DEV, "al_complete_io() called on inactive extent %u\n", enr);
+		return;
+	}
+
+	if (lc_put(mdev->act_log, extent) == 0)
+		wake_up(&mdev->al_wait);
+
+	spin_unlock_irqrestore(&mdev->al_lock, flags);
+}
+
+int
+w_al_write_transaction(struct drbd_conf *mdev, struct drbd_work *w, int unused)
+{
+	struct update_al_work *aw = (struct update_al_work *)w;
+	struct lc_element *updated = aw->al_ext;
+	const unsigned int new_enr = aw->enr;
+	const unsigned int evicted = aw->old_enr;
+	struct al_transaction *buffer;
+	sector_t sector;
+	int i, n, mx;
+	unsigned int extent_nr;
+	u32 xor_sum = 0;
+
+	if (!get_ldev(mdev)) {
+		dev_err(DEV, "get_ldev() failed in w_al_write_transaction\n");
+		complete(&((struct update_al_work *)w)->event);
+		return 1;
+	}
+	/* do we have to do a bitmap write, first?
+	 * TODO reduce maximum latency:
+	 * submit both bios, then wait for both,
+	 * instead of doing two synchronous sector writes. */
+	if (mdev->state.conn < C_CONNECTED && evicted != LC_FREE)
+		drbd_bm_write_sect(mdev, evicted/AL_EXT_PER_BM_SECT);
+
+	mutex_lock(&mdev->md_io_mutex); /* protects md_io_page, al_tr_cycle, ... */
+	buffer = (struct al_transaction *)page_address(mdev->md_io_page);
+
+	buffer->magic = __constant_cpu_to_be32(DRBD_MAGIC);
+	buffer->tr_number = cpu_to_be32(mdev->al_tr_number);
+
+	n = lc_index_of(mdev->act_log, updated);
+
+	buffer->updates[0].pos = cpu_to_be32(n);
+	buffer->updates[0].extent = cpu_to_be32(new_enr);
+
+	xor_sum ^= new_enr;
+
+	mx = min_t(int, AL_EXTENTS_PT,
+		   mdev->act_log->nr_elements - mdev->al_tr_cycle);
+	for (i = 0; i < mx; i++) {
+		unsigned idx = mdev->al_tr_cycle + i;
+		extent_nr = lc_element_by_index(mdev->act_log, idx)->lc_number;
+		buffer->updates[i+1].pos = cpu_to_be32(idx);
+		buffer->updates[i+1].extent = cpu_to_be32(extent_nr);
+		xor_sum ^= extent_nr;
+	}
+	for (; i < AL_EXTENTS_PT; i++) {
+		buffer->updates[i+1].pos = __constant_cpu_to_be32(-1);
+		buffer->updates[i+1].extent = __constant_cpu_to_be32(LC_FREE);
+		xor_sum ^= LC_FREE;
+	}
+	mdev->al_tr_cycle += AL_EXTENTS_PT;
+	if (mdev->al_tr_cycle >= mdev->act_log->nr_elements)
+		mdev->al_tr_cycle = 0;
+
+	buffer->xor_sum = cpu_to_be32(xor_sum);
+
+	sector =  mdev->ldev->md.md_offset
+		+ mdev->ldev->md.al_offset + mdev->al_tr_pos;
+
+	if (!drbd_md_sync_page_io(mdev, mdev->ldev, sector, WRITE)) {
+		drbd_chk_io_error(mdev, 1, TRUE);
+		drbd_io_error(mdev, TRUE);
+	}
+
+	if (++mdev->al_tr_pos >
+	    div_ceil(mdev->act_log->nr_elements, AL_EXTENTS_PT))
+		mdev->al_tr_pos = 0;
+
+	D_ASSERT(mdev->al_tr_pos < MD_AL_MAX_SIZE);
+	mdev->al_tr_number++;
+
+	mutex_unlock(&mdev->md_io_mutex);
+
+	complete(&((struct update_al_work *)w)->event);
+	put_ldev(mdev);
+
+	return 1;
+}
+
+/**
+ * drbd_al_read_tr() - Read a single transaction from the on disk activity log
+ * @mdev:	DRBD device.
+ * @bdev:	Block device to read form.
+ * @b:		pointer to an al_transaction.
+ * @index:	On disk slot of the transaction to read.
+ *
+ * Returns -1 on IO error, 0 on checksum error and 1 upon success.
+ */
+static int drbd_al_read_tr(struct drbd_conf *mdev,
+			   struct drbd_backing_dev *bdev,
+			   struct al_transaction *b,
+			   int index)
+{
+	sector_t sector;
+	int rv, i;
+	u32 xor_sum = 0;
+
+	sector = bdev->md.md_offset + bdev->md.al_offset + index;
+
+	/* Dont process error normally,
+	 * as this is done before disk is atached! */
+	if (!drbd_md_sync_page_io(mdev, bdev, sector, READ))
+		return -1;
+
+	rv = (be32_to_cpu(b->magic) == DRBD_MAGIC);
+
+	for (i = 0; i < AL_EXTENTS_PT + 1; i++)
+		xor_sum ^= be32_to_cpu(b->updates[i].extent);
+	rv &= (xor_sum == be32_to_cpu(b->xor_sum));
+
+	return rv;
+}
+
+/**
+ * drbd_al_read_log() - Restores the activity log from its on disk representation.
+ * @mdev:	DRBD device.
+ * @bdev:	Block device to read form.
+ *
+ * Returns 1 on success, returns 0 when reading the log failed due to IO errors.
+ */
+int drbd_al_read_log(struct drbd_conf *mdev, struct drbd_backing_dev *bdev)
+{
+	struct al_transaction *buffer;
+	int i;
+	int rv;
+	int mx;
+	int active_extents = 0;
+	int transactions = 0;
+	int found_valid = 0;
+	int from = 0;
+	int to = 0;
+	u32 from_tnr = 0;
+	u32 to_tnr = 0;
+	u32 cnr;
+
+	mx = div_ceil(mdev->act_log->nr_elements, AL_EXTENTS_PT);
+
+	/* lock out all other meta data io for now,
+	 * and make sure the page is mapped.
+	 */
+	mutex_lock(&mdev->md_io_mutex);
+	buffer = page_address(mdev->md_io_page);
+
+	/* Find the valid transaction in the log */
+	for (i = 0; i <= mx; i++) {
+		rv = drbd_al_read_tr(mdev, bdev, buffer, i);
+		if (rv == 0)
+			continue;
+		if (rv == -1) {
+			mutex_unlock(&mdev->md_io_mutex);
+			return 0;
+		}
+		cnr = be32_to_cpu(buffer->tr_number);
+
+		if (++found_valid == 1) {
+			from = i;
+			to = i;
+			from_tnr = cnr;
+			to_tnr = cnr;
+			continue;
+		}
+		if ((int)cnr - (int)from_tnr < 0) {
+			D_ASSERT(from_tnr - cnr + i - from == mx+1);
+			from = i;
+			from_tnr = cnr;
+		}
+		if ((int)cnr - (int)to_tnr > 0) {
+			D_ASSERT(cnr - to_tnr == i - to);
+			to = i;
+			to_tnr = cnr;
+		}
+	}
+
+	if (!found_valid) {
+		dev_warn(DEV, "No usable activity log found.\n");
+		mutex_unlock(&mdev->md_io_mutex);
+		return 1;
+	}
+
+	/* Read the valid transactions.
+	 * dev_info(DEV, "Reading from %d to %d.\n",from,to); */
+	i = from;
+	while (1) {
+		int j, pos;
+		unsigned int extent_nr;
+		unsigned int trn;
+
+		rv = drbd_al_read_tr(mdev, bdev, buffer, i);
+		ERR_IF(rv == 0) goto cancel;
+		if (rv == -1) {
+			mutex_unlock(&mdev->md_io_mutex);
+			return 0;
+		}
+
+		trn = be32_to_cpu(buffer->tr_number);
+
+		spin_lock_irq(&mdev->al_lock);
+
+		/* This loop runs backwards because in the cyclic
+		   elements there might be an old version of the
+		   updated element (in slot 0). So the element in slot 0
+		   can overwrite old versions. */
+		for (j = AL_EXTENTS_PT; j >= 0; j--) {
+			pos = be32_to_cpu(buffer->updates[j].pos);
+			extent_nr = be32_to_cpu(buffer->updates[j].extent);
+
+			if (extent_nr == LC_FREE)
+				continue;
+
+			lc_set(mdev->act_log, extent_nr, pos);
+			active_extents++;
+		}
+		spin_unlock_irq(&mdev->al_lock);
+
+		transactions++;
+
+cancel:
+		if (i == to)
+			break;
+		i++;
+		if (i > mx)
+			i = 0;
+	}
+
+	mdev->al_tr_number = to_tnr+1;
+	mdev->al_tr_pos = to;
+	if (++mdev->al_tr_pos >
+	    div_ceil(mdev->act_log->nr_elements, AL_EXTENTS_PT))
+		mdev->al_tr_pos = 0;
+
+	/* ok, we are done with it */
+	mutex_unlock(&mdev->md_io_mutex);
+
+	dev_info(DEV, "Found %d transactions (%d active extents) in activity log.\n",
+	     transactions, active_extents);
+
+	return 1;
+}
+
+static void atodb_endio(struct bio *bio, int error)
+{
+	struct drbd_atodb_wait *wc = bio->bi_private;
+	struct drbd_conf *mdev = wc->mdev;
+	struct page *page;
+	int uptodate = bio_flagged(bio, BIO_UPTODATE);
+
+	/* strange behaviour of some lower level drivers...
+	 * fail the request by clearing the uptodate flag,
+	 * but do not return any error?! */
+	if (!error && !uptodate)
+		error = -EIO;
+
+	/* corresponding drbd_io_error is in drbd_al_to_on_disk_bm */
+	drbd_chk_io_error(mdev, error, TRUE);
+	if (error && wc->error == 0)
+		wc->error = error;
+
+	if (atomic_dec_and_test(&wc->count))
+		complete(&wc->io_done);
+
+	page = bio->bi_io_vec[0].bv_page;
+	put_page(page);
+	bio_put(bio);
+	mdev->bm_writ_cnt++;
+	put_ldev(mdev);
+}
+
+#define S2W(s)	((s)<<(BM_EXT_SHIFT-BM_BLOCK_SHIFT-LN2_BPL))
+/* activity log to on disk bitmap -- prepare bio unless that sector
+ * is already covered by previously prepared bios */
+static int atodb_prepare_unless_covered(struct drbd_conf *mdev,
+					struct bio **bios,
+					unsigned int enr,
+					struct drbd_atodb_wait *wc) __must_hold(local)
+{
+	struct bio *bio;
+	struct page *page;
+	sector_t on_disk_sector = enr + mdev->ldev->md.md_offset
+				      + mdev->ldev->md.bm_offset;
+	unsigned int page_offset = PAGE_SIZE;
+	int offset;
+	int i = 0;
+	int err = -ENOMEM;
+
+	/* Check if that enr is already covered by an already created bio.
+	 * Caution, bios[] is not NULL terminated,
+	 * but only initialized to all NULL.
+	 * For completely scattered activity log,
+	 * the last invocation iterates over all bios,
+	 * and finds the last NULL entry.
+	 */
+	while ((bio = bios[i])) {
+		if (bio->bi_sector == on_disk_sector)
+			return 0;
+		i++;
+	}
+	/* bios[i] == NULL, the next not yet used slot */
+
+	bio = bio_alloc(GFP_KERNEL, 1);
+	if (bio == NULL)
+		return -ENOMEM;
+
+	if (i > 0) {
+		const struct bio_vec *prev_bv = bios[i-1]->bi_io_vec;
+		page_offset = prev_bv->bv_offset + prev_bv->bv_len;
+		page = prev_bv->bv_page;
+	}
+	if (page_offset == PAGE_SIZE) {
+		page = alloc_page(__GFP_HIGHMEM);
+		if (page == NULL)
+			goto out_bio_put;
+		page_offset = 0;
+	} else {
+		get_page(page);
+	}
+
+	offset = S2W(enr);
+	drbd_bm_get_lel(mdev, offset,
+			min_t(size_t, S2W(1), drbd_bm_words(mdev) - offset),
+			kmap(page) + page_offset);
+	kunmap(page);
+
+	bio->bi_private = wc;
+	bio->bi_end_io = atodb_endio;
+	bio->bi_bdev = mdev->ldev->md_bdev;
+	bio->bi_sector = on_disk_sector;
+
+	if (bio_add_page(bio, page, MD_SECTOR_SIZE, page_offset) != MD_SECTOR_SIZE)
+		goto out_put_page;
+
+	atomic_inc(&wc->count);
+	/* we already know that we may do this...
+	 * get_ldev_if_state(mdev,D_ATTACHING);
+	 * just get the extra reference, so that the local_cnt reflects
+	 * the number of pending IO requests DRBD at its backing device.
+	 */
+	atomic_inc(&mdev->local_cnt);
+
+	bios[i] = bio;
+
+	return 0;
+
+out_put_page:
+	err = -EINVAL;
+	put_page(page);
+out_bio_put:
+	bio_put(bio);
+	return err;
+}
+
+/**
+ * drbd_al_to_on_disk_bm() -  * Writes bitmap parts covered by active AL extents
+ * @mdev:	DRBD device.
+ *
+ * Called when we detach (unconfigure) local storage,
+ * or when we go from R_PRIMARY to R_SECONDARY role.
+ */
+void drbd_al_to_on_disk_bm(struct drbd_conf *mdev)
+{
+	int i, nr_elements;
+	unsigned int enr;
+	struct bio **bios;
+	struct drbd_atodb_wait wc;
+
+	ERR_IF (!get_ldev_if_state(mdev, D_ATTACHING))
+		return; /* sorry, I don't have any act_log etc... */
+
+	wait_event(mdev->al_wait, lc_try_lock(mdev->act_log));
+
+	nr_elements = mdev->act_log->nr_elements;
+
+	bios = kzalloc(sizeof(struct bio *) * nr_elements, GFP_KERNEL);
+	if (!bios)
+		goto submit_one_by_one;
+
+	atomic_set(&wc.count, 0);
+	init_completion(&wc.io_done);
+	wc.mdev = mdev;
+	wc.error = 0;
+
+	for (i = 0; i < nr_elements; i++) {
+		enr = lc_element_by_index(mdev->act_log, i)->lc_number;
+		if (enr == LC_FREE)
+			continue;
+		/* next statement also does atomic_inc wc.count and local_cnt */
+		if (atodb_prepare_unless_covered(mdev, bios,
+						enr/AL_EXT_PER_BM_SECT,
+						&wc))
+			goto free_bios_submit_one_by_one;
+	}
+
+	/* unneccessary optimization? */
+	lc_unlock(mdev->act_log);
+	wake_up(&mdev->al_wait);
+
+	/* all prepared, submit them */
+	for (i = 0; i < nr_elements; i++) {
+		if (bios[i] == NULL)
+			break;
+		if (FAULT_ACTIVE(mdev, DRBD_FAULT_MD_WR)) {
+			bios[i]->bi_rw = WRITE;
+			bio_endio(bios[i], -EIO);
+		} else {
+			submit_bio(WRITE, bios[i]);
+		}
+	}
+
+	drbd_blk_run_queue(bdev_get_queue(mdev->ldev->md_bdev));
+
+	/* always (try to) flush bitmap to stable storage */
+	drbd_md_flush(mdev);
+
+	/* In case we did not submit a single IO do not wait for
+	 * them to complete. ( Because we would wait forever here. )
+	 *
+	 * In case we had IOs and they are already complete, there
+	 * is not point in waiting anyways.
+	 * Therefore this if () ... */
+	if (atomic_read(&wc.count))
+		wait_for_completion(&wc.io_done);
+
+	put_ldev(mdev);
+
+	if (wc.error)
+		drbd_io_error(mdev, TRUE);
+	kfree(bios);
+	return;
+
+ free_bios_submit_one_by_one:
+	/* free everything by calling the endio callback directly. */
+	for (i = 0; i < nr_elements && bios[i]; i++)
+		bio_endio(bios[i], 0);
+
+	kfree(bios);
+
+ submit_one_by_one:
+	dev_warn(DEV, "Using the slow drbd_al_to_on_disk_bm()\n");
+
+	for (i = 0; i < mdev->act_log->nr_elements; i++) {
+		enr = lc_element_by_index(mdev->act_log, i)->lc_number;
+		if (enr == LC_FREE)
+			continue;
+		/* Really slow: if we have al-extents 16..19 active,
+		 * sector 4 will be written four times! Synchronous! */
+		drbd_bm_write_sect(mdev, enr/AL_EXT_PER_BM_SECT);
+	}
+
+	lc_unlock(mdev->act_log);
+	wake_up(&mdev->al_wait);
+	put_ldev(mdev);
+}
+
+/**
+ * drbd_al_apply_to_bm() - Sets the bitmap to diry(1) where covered ba active AL extents
+ * @mdev:	DRBD device.
+ */
+void drbd_al_apply_to_bm(struct drbd_conf *mdev)
+{
+	unsigned int enr;
+	unsigned long add = 0;
+	char ppb[10];
+	int i;
+
+	wait_event(mdev->al_wait, lc_try_lock(mdev->act_log));
+
+	for (i = 0; i < mdev->act_log->nr_elements; i++) {
+		enr = lc_element_by_index(mdev->act_log, i)->lc_number;
+		if (enr == LC_FREE)
+			continue;
+		add += drbd_bm_ALe_set_all(mdev, enr);
+	}
+
+	lc_unlock(mdev->act_log);
+	wake_up(&mdev->al_wait);
+
+	dev_info(DEV, "Marked additional %s as out-of-sync based on AL.\n",
+	     ppsize(ppb, Bit2KB(add)));
+}
+
+static int _try_lc_del(struct drbd_conf *mdev, struct lc_element *al_ext)
+{
+	int rv;
+
+	spin_lock_irq(&mdev->al_lock);
+	rv = (al_ext->refcnt == 0);
+	if (likely(rv))
+		lc_del(mdev->act_log, al_ext);
+	spin_unlock_irq(&mdev->al_lock);
+
+	return rv;
+}
+
+/**
+ * drbd_al_shrink() - Removes all active extents form the activity log
+ * @mdev:	DRBD device.
+ *
+ * Removes all active extents form the activity log, waiting until
+ * the reference count of each etry dropped to 0 first, of course.
+ *
+ * You need to lock mdev->act_log with lc_try_lock() / lc_unlock()
+ */
+void drbd_al_shrink(struct drbd_conf *mdev)
+{
+	struct lc_element *al_ext;
+	int i;
+
+	D_ASSERT(test_bit(__LC_DIRTY, &mdev->act_log->flags));
+
+	for (i = 0; i < mdev->act_log->nr_elements; i++) {
+		al_ext = lc_element_by_index(mdev->act_log, i);
+		if (al_ext->lc_number == LC_FREE)
+			continue;
+		wait_event(mdev->al_wait, _try_lc_del(mdev, al_ext));
+	}
+
+	wake_up(&mdev->al_wait);
+}
+
+static int w_update_odbm(struct drbd_conf *mdev, struct drbd_work *w, int unused)
+{
+	struct update_odbm_work *udw = (struct update_odbm_work *)w;
+
+	if (!get_ldev(mdev)) {
+		if (__ratelimit(&drbd_ratelimit_state))
+			dev_warn(DEV, "Can not update on disk bitmap, local IO disabled.\n");
+		return 1;
+	}
+
+	drbd_bm_write_sect(mdev, udw->enr);
+	put_ldev(mdev);
+
+	kfree(udw);
+
+	if (drbd_bm_total_weight(mdev) <= mdev->rs_failed) {
+		switch (mdev->state.conn) {
+		case C_SYNC_SOURCE:  case C_SYNC_TARGET:
+		case C_PAUSED_SYNC_S: case C_PAUSED_SYNC_T:
+			drbd_resync_finished(mdev);
+		default:
+			/* nothing to do */
+			break;
+		}
+	}
+	drbd_bcast_sync_progress(mdev);
+
+	return 1;
+}
+
+
+/* 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.
+ *
+ * TODO will be obsoleted once we have a caching lru of the on disk bitmap
+ */
+static void drbd_try_clear_on_disk_bm(struct drbd_conf *mdev, sector_t sector,
+				      int count, int success)
+{
+	struct lc_element *e;
+	struct update_odbm_work *udw;
+
+	unsigned int enr;
+
+	D_ASSERT(atomic_read(&mdev->local_cnt));
+
+	/* I simply assume that a sector/size pair never crosses
+	 * a 16 MB extent border. (Currently this is true...) */
+	enr = BM_SECT_TO_EXT(sector);
+
+	e = lc_get(mdev->resync, enr);
+	if (e) {
+		struct bm_extent *ext = lc_entry(e, struct bm_extent, lce);
+		if (ext->lce.lc_number == enr) {
+			if (success)
+				ext->rs_left -= count;
+			else
+				ext->rs_failed += count;
+			if (ext->rs_left < ext->rs_failed) {
+				dev_err(DEV, "BAD! sector=%llus enr=%u rs_left=%d "
+				    "rs_failed=%d count=%d\n",
+				     (unsigned long long)sector,
+				     ext->lce.lc_number, ext->rs_left,
+				     ext->rs_failed, count);
+				dump_stack();
+
+				lc_put(mdev->resync, &ext->lce);
+				drbd_force_state(mdev, NS(conn, C_DISCONNECTING));
+				return;
+			}
+		} 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(mdev, enr);
+			if (ext->flags != 0) {
+				dev_warn(DEV, "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) {
+				dev_warn(DEV, "Kicking resync_lru element enr=%u "
+				     "out with rs_failed=%d\n",
+				     ext->lce.lc_number, ext->rs_failed);
+				set_bit(WRITE_BM_AFTER_RESYNC, &mdev->flags);
+			}
+			ext->rs_left = rs_left;
+			ext->rs_failed = success ? 0 : count;
+			lc_changed(mdev->resync, &ext->lce);
+		}
+		lc_put(mdev->resync, &ext->lce);
+		/* no race, we are within the al_lock! */
+
+		if (ext->rs_left == ext->rs_failed) {
+			ext->rs_failed = 0;
+
+			udw = kmalloc(sizeof(*udw), GFP_ATOMIC);
+			if (udw) {
+				udw->enr = ext->lce.lc_number;
+				udw->w.cb = w_update_odbm;
+				drbd_queue_work_front(&mdev->data.work, &udw->w);
+			} else {
+				dev_warn(DEV, "Could not kmalloc an udw\n");
+				set_bit(WRITE_BM_AFTER_RESYNC, &mdev->flags);
+			}
+		}
+	} else {
+		dev_err(DEV, "lc_get() failed! locked=%d/%d flags=%lu\n",
+		    mdev->resync_locked,
+		    mdev->resync->nr_elements,
+		    mdev->resync->flags);
+	}
+}
+
+/* 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.
+ *
+ */
+void __drbd_set_in_sync(struct drbd_conf *mdev, sector_t sector, int size,
+		       const char *file, const unsigned int line)
+{
+	/* Is called from worker and receiver context _only_ */
+	unsigned long sbnr, ebnr, lbnr;
+	unsigned long count = 0;
+	sector_t esector, nr_sectors;
+	int wake_up = 0;
+	unsigned long flags;
+
+	if (size <= 0 || (size & 0x1ff) != 0 || size > DRBD_MAX_SEGMENT_SIZE) {
+		dev_err(DEV, "drbd_set_in_sync: sector=%llus size=%d nonsense!\n",
+				(unsigned long long)sector, size);
+		return;
+	}
+	nr_sectors = drbd_get_capacity(mdev->this_bdev);
+	esector = sector + (size >> 9) - 1;
+
+	ERR_IF(sector >= nr_sectors) return;
+	ERR_IF(esector >= nr_sectors) esector = (nr_sectors-1);
+
+	lbnr = BM_SECT_TO_BIT(nr_sectors-1);
+
+	/* we clear it (in sync).
+	 * round up start sector, round down end sector.  we make sure we only
+	 * clear full, alligned, BM_BLOCK_SIZE (4K) blocks */
+	if (unlikely(esector < BM_SECT_PER_BIT-1))
+		return;
+	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);
+
+	trace_drbd_resync(mdev, TRACE_LVL_METRICS,
+			  "drbd_set_in_sync: sector=%llus size=%u sbnr=%lu ebnr=%lu\n",
+			  (unsigned long long)sector, size, sbnr, ebnr);
+
+	if (sbnr > ebnr)
+		return;
+
+	/*
+	 * ok, (capacity & 7) != 0 sometimes, but who cares...
+	 * we count rs_{total,left} in bits, not sectors.
+	 */
+	spin_lock_irqsave(&mdev->al_lock, flags);
+	count = drbd_bm_clear_bits(mdev, sbnr, ebnr);
+	if (count) {
+		/* we need the lock for drbd_try_clear_on_disk_bm */
+		if (jiffies - mdev->rs_mark_time > HZ*10) {
+			/* should be roling marks,
+			 * but we estimate only anyways. */
+			if (mdev->rs_mark_left != drbd_bm_total_weight(mdev) &&
+			    mdev->state.conn != C_PAUSED_SYNC_T &&
+			    mdev->state.conn != C_PAUSED_SYNC_S) {
+				mdev->rs_mark_time = jiffies;
+				mdev->rs_mark_left = drbd_bm_total_weight(mdev);
+			}
+		}
+		if (get_ldev(mdev)) {
+			drbd_try_clear_on_disk_bm(mdev, sector, count, TRUE);
+			put_ldev(mdev);
+		}
+		/* just wake_up unconditional now, various lc_chaged(),
+		 * lc_put() in drbd_try_clear_on_disk_bm(). */
+		wake_up = 1;
+	}
+	spin_unlock_irqrestore(&mdev->al_lock, flags);
+	if (wake_up)
+		wake_up(&mdev->al_wait);
+}
+
+/*
+ * this is intended to set one request worth of data out of sync.
+ * affects at least 1 bit,
+ * and at most 1+DRBD_MAX_SEGMENT_SIZE/BM_BLOCK_SIZE bits.
+ *
+ * called by tl_clear and drbd_send_dblock (==drbd_make_request).
+ * so this can be _any_ process.
+ */
+void __drbd_set_out_of_sync(struct drbd_conf *mdev, sector_t sector, int size,
+			    const char *file, const unsigned int line)
+{
+	unsigned long sbnr, ebnr, lbnr, flags;
+	sector_t esector, nr_sectors;
+	unsigned int enr, count;
+	struct lc_element *e;
+
+	if (size <= 0 || (size & 0x1ff) != 0 || size > DRBD_MAX_SEGMENT_SIZE) {
+		dev_err(DEV, "sector: %llus, size: %d\n",
+			(unsigned long long)sector, size);
+		return;
+	}
+
+	if (!get_ldev(mdev))
+		return; /* no disk, no metadata, no bitmap to set bits in */
+
+	nr_sectors = drbd_get_capacity(mdev->this_bdev);
+	esector = sector + (size >> 9) - 1;
+
+	ERR_IF(sector >= nr_sectors)
+		goto out;
+	ERR_IF(esector >= nr_sectors)
+		esector = (nr_sectors-1);
+
+	lbnr = BM_SECT_TO_BIT(nr_sectors-1);
+
+	/* we set it out of sync,
+	 * we do not need to round anything here */
+	sbnr = BM_SECT_TO_BIT(sector);
+	ebnr = BM_SECT_TO_BIT(esector);
+
+	trace_drbd_resync(mdev, TRACE_LVL_METRICS,
+			  "drbd_set_out_of_sync: sector=%llus size=%u sbnr=%lu ebnr=%lu\n",
+			  (unsigned long long)sector, size, sbnr, ebnr);
+
+	/* ok, (capacity & 7) != 0 sometimes, but who cares...
+	 * we count rs_{total,left} in bits, not sectors.  */
+	spin_lock_irqsave(&mdev->al_lock, flags);
+	count = drbd_bm_set_bits(mdev, sbnr, ebnr);
+
+	enr = BM_SECT_TO_EXT(sector);
+	e = lc_find(mdev->resync, enr);
+	if (e)
+		lc_entry(e, struct bm_extent, lce)->rs_left += count;
+	spin_unlock_irqrestore(&mdev->al_lock, flags);
+
+out:
+	put_ldev(mdev);
+}
+
+static
+struct bm_extent *_bme_get(struct drbd_conf *mdev, unsigned int enr)
+{
+	struct lc_element *e;
+	struct bm_extent *bm_ext;
+	int wakeup = 0;
+	unsigned long rs_flags;
+
+	spin_lock_irq(&mdev->al_lock);
+	if (mdev->resync_locked > mdev->resync->nr_elements/2) {
+		spin_unlock_irq(&mdev->al_lock);
+		return NULL;
+	}
+	e = lc_get(mdev->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(mdev, enr);
+			bm_ext->rs_failed = 0;
+			lc_changed(mdev->resync, &bm_ext->lce);
+			wakeup = 1;
+		}
+		if (bm_ext->lce.refcnt == 1)
+			mdev->resync_locked++;
+		set_bit(BME_NO_WRITES, &bm_ext->flags);
+	}
+	rs_flags = mdev->resync->flags;
+	spin_unlock_irq(&mdev->al_lock);
+	if (wakeup)
+		wake_up(&mdev->al_wait);
+
+	if (!bm_ext) {
+		if (rs_flags & LC_STARVING)
+			dev_warn(DEV, "Have to wait for element"
+			     " (resync LRU too small?)\n");
+		BUG_ON(rs_flags & LC_DIRTY);
+	}
+
+	return bm_ext;
+}
+
+static int _is_in_al(struct drbd_conf *mdev, unsigned int enr)
+{
+	struct lc_element *al_ext;
+	int rv = 0;
+
+	spin_lock_irq(&mdev->al_lock);
+	if (unlikely(enr == mdev->act_log->new_number))
+		rv = 1;
+	else {
+		al_ext = lc_find(mdev->act_log, enr);
+		if (al_ext) {
+			if (al_ext->refcnt)
+				rv = 1;
+		}
+	}
+	spin_unlock_irq(&mdev->al_lock);
+
+	/*
+	if (unlikely(rv)) {
+		dev_info(DEV, "Delaying sync read until app's write is done\n");
+	}
+	*/
+	return rv;
+}
+
+/**
+ * drbd_rs_begin_io() - Gets an extent in the resync LRU cache and sets it to BME_LOCKED
+ * @mdev:	DRBD device.
+ * @sector:	The sector number.
+ *
+ * This functions sleeps on al_wait. Returns 1 on success, 0 if interrupted.
+ */
+int drbd_rs_begin_io(struct drbd_conf *mdev, sector_t sector)
+{
+	unsigned int enr = BM_SECT_TO_EXT(sector);
+	struct bm_extent *bm_ext;
+	int i, sig;
+
+	trace_drbd_resync(mdev, TRACE_LVL_ALL,
+			  "drbd_rs_begin_io: sector=%llus (rs_end=%d)\n",
+			  (unsigned long long)sector, enr);
+
+	sig = wait_event_interruptible(mdev->al_wait,
+			(bm_ext = _bme_get(mdev, enr)));
+	if (sig)
+		return 0;
+
+	if (test_bit(BME_LOCKED, &bm_ext->flags))
+		return 1;
+
+	for (i = 0; i < AL_EXT_PER_BM_SECT; i++) {
+		sig = wait_event_interruptible(mdev->al_wait,
+				!_is_in_al(mdev, enr * AL_EXT_PER_BM_SECT + i));
+		if (sig) {
+			spin_lock_irq(&mdev->al_lock);
+			if (lc_put(mdev->resync, &bm_ext->lce) == 0) {
+				clear_bit(BME_NO_WRITES, &bm_ext->flags);
+				mdev->resync_locked--;
+				wake_up(&mdev->al_wait);
+			}
+			spin_unlock_irq(&mdev->al_lock);
+			return 0;
+		}
+	}
+
+	set_bit(BME_LOCKED, &bm_ext->flags);
+
+	return 1;
+}
+
+/**
+ * drbd_try_rs_begin_io() - Gets an extent in the resync LRU cache, does not sleep
+ * @mdev:	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_conf *mdev, sector_t sector)
+{
+	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;
+
+	trace_drbd_resync(mdev, TRACE_LVL_ALL, "drbd_try_rs_begin_io: sector=%llus\n",
+			  (unsigned long long)sector);
+
+	spin_lock_irq(&mdev->al_lock);
+	if (mdev->resync_wenr != LC_FREE && mdev->resync_wenr != enr) {
+		/* in case you have very heavy scattered io, it may
+		 * stall the syncer undefined if we giveup 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 keept the refcount on.
+		 * so we remembered which extent we had to try agin, and
+		 * if the next requested one is something else, we do
+		 * the lc_put here...
+		 * we also have to wake_up
+		 */
+
+		trace_drbd_resync(mdev, TRACE_LVL_ALL,
+				  "dropping %u, aparently got 'synced' by application io\n",
+				  mdev->resync_wenr);
+
+		e = lc_find(mdev->resync, mdev->resync_wenr);
+		bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
+		if (bm_ext) {
+			D_ASSERT(!test_bit(BME_LOCKED, &bm_ext->flags));
+			D_ASSERT(test_bit(BME_NO_WRITES, &bm_ext->flags));
+			clear_bit(BME_NO_WRITES, &bm_ext->flags);
+			mdev->resync_wenr = LC_FREE;
+			if (lc_put(mdev->resync, &bm_ext->lce) == 0)
+				mdev->resync_locked--;
+			wake_up(&mdev->al_wait);
+		} else {
+			dev_alert(DEV, "LOGIC BUG\n");
+		}
+	}
+	/* TRY. */
+	e = lc_try_get(mdev->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)) {
+			mdev->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. */
+			trace_drbd_resync(mdev, TRACE_LVL_ALL,
+					  "dropping extra reference on %u\n", enr);
+
+			bm_ext->lce.refcnt--;
+			D_ASSERT(bm_ext->lce.refcnt > 0);
+		}
+		goto check_al;
+	} else {
+		/* do we rather want to try later? */
+		if (mdev->resync_locked > mdev->resync->nr_elements-3) {
+			trace_drbd_resync(mdev, TRACE_LVL_ALL,
+					  "resync_locked = %u!\n", mdev->resync_locked);
+
+			goto try_again;
+		}
+		/* Do or do not. There is no try. -- Joda */
+		e = lc_get(mdev->resync, enr);
+		bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
+		if (!bm_ext) {
+			const unsigned long rs_flags = mdev->resync->flags;
+			if (rs_flags & LC_STARVING)
+				dev_warn(DEV, "Have to wait for element"
+				     " (resync LRU too small?)\n");
+			BUG_ON(rs_flags & LC_DIRTY);
+			goto try_again;
+		}
+		if (bm_ext->lce.lc_number != enr) {
+			bm_ext->rs_left = drbd_bm_e_weight(mdev, enr);
+			bm_ext->rs_failed = 0;
+			lc_changed(mdev->resync, &bm_ext->lce);
+			wake_up(&mdev->al_wait);
+			D_ASSERT(test_bit(BME_LOCKED, &bm_ext->flags) == 0);
+		}
+		set_bit(BME_NO_WRITES, &bm_ext->flags);
+		D_ASSERT(bm_ext->lce.refcnt == 1);
+		mdev->resync_locked++;
+		goto check_al;
+	}
+check_al:
+	trace_drbd_resync(mdev, TRACE_LVL_ALL, "checking al for %u\n", enr);
+
+	for (i = 0; i < AL_EXT_PER_BM_SECT; i++) {
+		if (unlikely(al_enr+i == mdev->act_log->new_number))
+			goto try_again;
+		if (lc_is_used(mdev->act_log, al_enr+i))
+			goto try_again;
+	}
+	set_bit(BME_LOCKED, &bm_ext->flags);
+proceed:
+	mdev->resync_wenr = LC_FREE;
+	spin_unlock_irq(&mdev->al_lock);
+	return 0;
+
+try_again:
+	trace_drbd_resync(mdev, TRACE_LVL_ALL, "need to try again for %u\n", enr);
+	if (bm_ext)
+		mdev->resync_wenr = enr;
+	spin_unlock_irq(&mdev->al_lock);
+	return -EAGAIN;
+}
+
+void drbd_rs_complete_io(struct drbd_conf *mdev, sector_t sector)
+{
+	unsigned int enr = BM_SECT_TO_EXT(sector);
+	struct lc_element *e;
+	struct bm_extent *bm_ext;
+	unsigned long flags;
+
+	trace_drbd_resync(mdev, TRACE_LVL_ALL,
+			  "drbd_rs_complete_io: sector=%llus (rs_enr=%d)\n",
+			  (long long)sector, enr);
+
+	spin_lock_irqsave(&mdev->al_lock, flags);
+	e = lc_find(mdev->resync, enr);
+	bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
+	if (!bm_ext) {
+		spin_unlock_irqrestore(&mdev->al_lock, flags);
+		dev_err(DEV, "drbd_rs_complete_io() called, but extent not found\n");
+		return;
+	}
+
+	if (bm_ext->lce.refcnt == 0) {
+		spin_unlock_irqrestore(&mdev->al_lock, flags);
+		dev_err(DEV, "drbd_rs_complete_io(,%llu [=%u]) called, "
+		    "but refcnt is 0!?\n",
+		    (unsigned long long)sector, enr);
+		return;
+	}
+
+	if (lc_put(mdev->resync, &bm_ext->lce) == 0) {
+		clear_bit(BME_LOCKED, &bm_ext->flags);
+		clear_bit(BME_NO_WRITES, &bm_ext->flags);
+		mdev->resync_locked--;
+		wake_up(&mdev->al_wait);
+	}
+
+	spin_unlock_irqrestore(&mdev->al_lock, flags);
+}
+
+/**
+ * drbd_rs_cancel_all() - Removes all extents from the resync LRU (even BME_LOCKED)
+ * @mdev:	DRBD device.
+ */
+void drbd_rs_cancel_all(struct drbd_conf *mdev)
+{
+	trace_drbd_resync(mdev, TRACE_LVL_METRICS, "drbd_rs_cancel_all\n");
+
+	spin_lock_irq(&mdev->al_lock);
+
+	if (get_ldev_if_state(mdev, D_FAILED)) { /* Makes sure ->resync is there. */
+		lc_reset(mdev->resync);
+		put_ldev(mdev);
+	}
+	mdev->resync_locked = 0;
+	mdev->resync_wenr = LC_FREE;
+	spin_unlock_irq(&mdev->al_lock);
+	wake_up(&mdev->al_wait);
+}
+
+/**
+ * drbd_rs_del_all() - Gracefully remove all extents from the resync LRU
+ * @mdev:	DRBD device.
+ *
+ * Returns 0 upon success, -EAGAIN if at least one reference count was
+ * not zero.
+ */
+int drbd_rs_del_all(struct drbd_conf *mdev)
+{
+	struct lc_element *e;
+	struct bm_extent *bm_ext;
+	int i;
+
+	trace_drbd_resync(mdev, TRACE_LVL_METRICS, "drbd_rs_del_all\n");
+
+	spin_lock_irq(&mdev->al_lock);
+
+	if (get_ldev_if_state(mdev, D_FAILED)) {
+		/* ok, ->resync is there. */
+		for (i = 0; i < mdev->resync->nr_elements; i++) {
+			e = lc_element_by_index(mdev->resync, i);
+			bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
+			if (bm_ext->lce.lc_number == LC_FREE)
+				continue;
+			if (bm_ext->lce.lc_number == mdev->resync_wenr) {
+				dev_info(DEV, "dropping %u in drbd_rs_del_all, apparently"
+				     " got 'synced' by application io\n",
+				     mdev->resync_wenr);
+				D_ASSERT(!test_bit(BME_LOCKED, &bm_ext->flags));
+				D_ASSERT(test_bit(BME_NO_WRITES, &bm_ext->flags));
+				clear_bit(BME_NO_WRITES, &bm_ext->flags);
+				mdev->resync_wenr = LC_FREE;
+				lc_put(mdev->resync, &bm_ext->lce);
+			}
+			if (bm_ext->lce.refcnt != 0) {
+				dev_info(DEV, "Retrying drbd_rs_del_all() later. "
+				     "refcnt=%d\n", bm_ext->lce.refcnt);
+				put_ldev(mdev);
+				spin_unlock_irq(&mdev->al_lock);
+				return -EAGAIN;
+			}
+			D_ASSERT(!test_bit(BME_LOCKED, &bm_ext->flags));
+			D_ASSERT(!test_bit(BME_NO_WRITES, &bm_ext->flags));
+			lc_del(mdev->resync, &bm_ext->lce);
+		}
+		D_ASSERT(mdev->resync->used == 0);
+		put_ldev(mdev);
+	}
+	spin_unlock_irq(&mdev->al_lock);
+
+	return 0;
+}
+
+/**
+ * drbd_rs_failed_io() - Record information on a failure to resync the specified blocks
+ * @mdev:	DRBD device.
+ * @sector:	The sector number.
+ * @size:	Size of failed IO operation, in byte.
+ */
+void drbd_rs_failed_io(struct drbd_conf *mdev, sector_t sector, int size)
+{
+	/* Is called from worker and receiver context _only_ */
+	unsigned long sbnr, ebnr, lbnr;
+	unsigned long count;
+	sector_t esector, nr_sectors;
+	int wake_up = 0;
+
+	trace_drbd_resync(mdev, TRACE_LVL_SUMMARY,
+			  "drbd_rs_failed_io: sector=%llus, size=%u\n",
+			  (unsigned long long)sector, size);
+
+	if (size <= 0 || (size & 0x1ff) != 0 || size > DRBD_MAX_SEGMENT_SIZE) {
+		dev_err(DEV, "drbd_rs_failed_io: sector=%llus size=%d nonsense!\n",
+				(unsigned long long)sector, size);
+		return;
+	}
+	nr_sectors = drbd_get_capacity(mdev->this_bdev);
+	esector = sector + (size >> 9) - 1;
+
+	ERR_IF(sector >= nr_sectors) return;
+	ERR_IF(esector >= nr_sectors) esector = (nr_sectors-1);
+
+	lbnr = BM_SECT_TO_BIT(nr_sectors-1);
+
+	/*
+	 * round up start sector, round down end sector.  we make sure we only
+	 * handle full, alligned, BM_BLOCK_SIZE (4K) blocks */
+	if (unlikely(esector < BM_SECT_PER_BIT-1))
+		return;
+	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);
+
+	if (sbnr > ebnr)
+		return;
+
+	/*
+	 * ok, (capacity & 7) != 0 sometimes, but who cares...
+	 * we count rs_{total,left} in bits, not sectors.
+	 */
+	spin_lock_irq(&mdev->al_lock);
+	count = drbd_bm_count_bits(mdev, sbnr, ebnr);
+	if (count) {
+		mdev->rs_failed += count;
+
+		if (get_ldev(mdev)) {
+			drbd_try_clear_on_disk_bm(mdev, sector, count, FALSE);
+			put_ldev(mdev);
+		}
+
+		/* just wake_up unconditional now, various lc_chaged(),
+		 * lc_put() in drbd_try_clear_on_disk_bm(). */
+		wake_up = 1;
+	}
+	spin_unlock_irq(&mdev->al_lock);
+	if (wake_up)
+		wake_up(&mdev->al_wait);
+}
--
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