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authorMikulas Patocka <mpatocka@redhat.com>2009-04-02 22:55:26 +0400
committerAlasdair G Kergon <agk@redhat.com>2009-04-02 22:55:26 +0400
commit35bf659b008e83e725dcd30f542e38461dbb867c (patch)
tree40be2f357f0905573bd4d21ff59e0db3cda26442
parentc66213921c816f6b1b16a84911618ba9a363b134 (diff)
downloadlinux-35bf659b008e83e725dcd30f542e38461dbb867c.tar.xz
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>
-rw-r--r--drivers/md/dm-snap.c13
1 files changed, 13 insertions, 0 deletions
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);