[PATCH] dm snapshot: fix kcopyd destructor

Before removing a snapshot, wait for the completion of any kcopyd jobs using
it.

Do this by maintaining a count (nr_jobs) of how many outstanding jobs each
kcopyd_client has.

The snapshot destructor first unregisters the snapshot so that no new kcopyd
jobs (created by writes to the origin) will reference that particular
snapshot.  kcopyd_client_destroy() is now run next to wait for the completion
of any outstanding jobs before the snapshot exception structures (that those
jobs reference) are freed.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index a5765f9fbe02..08312b46463a 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -559,8 +559,12 @@ static void snapshot_dtr(struct dm_target *ti)
 {
         struct dm_snapshot *s = (struct dm_snapshot *) ti->private;
 
+        /* Prevent further origin writes from using this snapshot. */
+        /* After this returns there can be no new kcopyd jobs. */
         unregister_snapshot(s);
 
+        kcopyd_client_destroy(s->kcopyd_client);
+
         exit_exception_table(&s->pending, pending_cache);
         exit_exception_table(&s->complete, exception_cache);
 
@@ -569,7 +573,7 @@ static void snapshot_dtr(struct dm_target *ti)
 
         dm_put_device(ti, s->origin);
         dm_put_device(ti, s->cow);
-        kcopyd_client_destroy(s->kcopyd_client);
+
         kfree(s);
 }