From: Mikulas Patocka Date: Fri, 3 Apr 2009 17:45:14 +0000 (+0000) Subject: dm snapshot: avoid having two exceptions for the same chunk X-Git-Tag: v2.6.29.2~61 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=8068bd7e0480e6295b9e0be85a2eb57f9aba7825;p=karo-tx-linux.git dm snapshot: avoid having two exceptions for the same chunk upstream commit: 35bf659b008e83e725dcd30f542e38461dbb867c We need to check if the exception was completed after dropping the lock. After regaining the lock, __find_pending_exception checks if the exception was already placed into &s->pending hash. But we don't check if the exception was already completed and placed into &s->complete hash. If the process waiting in alloc_pending_exception was delayed at this point because of a scheduling latency and the exception was meanwhile completed, we'd miss that and allocate another pending exception for already completed chunk. It would lead to a situation where two records for the same chunk exist and potential data corruption because multiple snapshot I/Os to the affected chunk could be redirected to different locations in the snapshot. Cc: stable@kernel.org Signed-off-by: Mikulas Patocka Signed-off-by: Alasdair G Kergon Signed-off-by: Chris Wright --- diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c index eb7291a84203..462750c66319 100644 --- a/drivers/md/dm-snap.c +++ b/drivers/md/dm-snap.c @@ -1080,6 +1080,13 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio, goto out_unlock; } + e = lookup_exception(&s->complete, chunk); + if (e) { + free_pending_exception(pe); + remap_exception(s, e, bio, chunk); + goto out_unlock; + } + pe = __find_pending_exception(s, pe, chunk); if (!pe) { __invalidate_snapshot(s, -ENOMEM); @@ -1226,6 +1233,12 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio) goto next_snapshot; } + e = lookup_exception(&snap->complete, chunk); + if (e) { + free_pending_exception(pe); + goto next_snapshot; + } + pe = __find_pending_exception(snap, pe, chunk); if (!pe) { __invalidate_snapshot(snap, -ENOMEM);