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Commit c6621392 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon
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dm snapshot: avoid dropping lock in __find_pending_exception 



It is uncommon and bug-prone to drop a lock in a function that is called with
the lock held, so this is moved to the caller.

Cc: stable@kernel.org
Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 2913808e

drivers/md/dm-snap.c

+24 −18
Original line number Diff line number Diff line
@@ -992,23 +992,10 @@ __lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk) 
 * this.

 */

static struct dm_snap_pending_exception *

__find_pending_exception(struct dm_snapshot *s, struct bio *bio)

__find_pending_exception(struct dm_snapshot *s,

			 struct dm_snap_pending_exception *pe, chunk_t chunk)

{

	struct dm_snap_pending_exception *pe, *pe2;

	chunk_t chunk = sector_to_chunk(s, bio->bi_sector);



	/*

	 * Create a new pending exception, we don't want

	 * to hold the lock while we do this.

	 */

	up_write(&s->lock);

	pe = alloc_pending_exception(s);

	down_write(&s->lock);



	if (!s->valid) {

		free_pending_exception(pe);

		return NULL;

	}

	struct dm_snap_pending_exception *pe2;



	pe2 = __lookup_pending_exception(s, chunk);

	if (pe2) {
@@ -1083,7 +1070,17 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio, 
	if (bio_rw(bio) == WRITE) {

		pe = __lookup_pending_exception(s, chunk);

		if (!pe) {

			pe = __find_pending_exception(s, bio);

			up_write(&s->lock);

			pe = alloc_pending_exception(s);

			down_write(&s->lock);



			if (!s->valid) {

				free_pending_exception(pe);

				r = -EIO;

				goto out_unlock;

			}



			pe = __find_pending_exception(s, pe, chunk);

			if (!pe) {

				__invalidate_snapshot(s, -ENOMEM);

				r = -EIO;
@@ -1220,7 +1217,16 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio) 


		pe = __lookup_pending_exception(snap, chunk);

		if (!pe) {

			pe = __find_pending_exception(snap, bio);

			up_write(&snap->lock);

			pe = alloc_pending_exception(snap);

			down_write(&snap->lock);



			if (!snap->valid) {

				free_pending_exception(pe);

				goto next_snapshot;

			}



			pe = __find_pending_exception(snap, pe, chunk);

			if (!pe) {

				__invalidate_snapshot(snap, -ENOMEM);

				goto next_snapshot;