Gitweb: http://git.kernel.org/linus/35bf659b008e83e725dcd30f542e38461dbb867c
Commit: 35bf659b008e83e725dcd30f542e38461dbb867c
Parent: c66213921c816f6b1b16a84911618ba9a363b134
Author: Mikulas Patocka <mpatocka@redhat.com>
AuthorDate: Thu Apr 2 19:55:26 2009 +0100
Committer: Alasdair G Kergon <agk@redhat.com>
CommitDate: Thu Apr 2 19:55:26 2009 +0100
dm snapshot: avoid having two exceptions for the same chunk
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 <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
---
drivers/md/dm-snap.c | 13 +++++++++++++
1 files changed, 13 insertions(+), 0 deletions(-)
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index eb7291a..462750c 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);
--
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