[100/151] dm snapshot: only take lock for statustype info not table

Greg KH
2009-12-17T04:25:12Z

From: Mikulas Patocka <mpatocka@redhat.com>

commit 94e76572b5dd37b1f0f4b3742ee8a565daead932 upstream.

Take snapshot lock only for STATUSTYPE_INFO, not STATUSTYPE_TABLE.

Commit 4c6fff445d7aa753957856278d4d93bcad6e2c14
(dm-snapshot-lock-snapshot-while-supplying-status.patch)
introduced this use of the lock, but userspace applications using
libdevmapper have been found to request STATUSTYPE_TABLE while the device
is suspended and the lock is already held, leading to deadlock. Since
the lock is not necessary in this case, don't try to take it.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/md/dm-snap.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1152,10 +1152,11 @@ static int snapshot_status(struct dm_tar
unsigned sz = 0;
struct dm_snapshot *snap = ti->private;

- down_write(&snap->lock);
-
switch (type) {
case STATUSTYPE_INFO:
+
+ down_write(&snap->lock);
+
if (!snap->valid)
DMEMIT("Invalid");
else {
@@ -1171,6 +1172,9 @@ static int snapshot_status(struct dm_tar
else
DMEMIT("Unknown");
}
+
+ up_write(&snap->lock);
+
break;

case STATUSTYPE_TABLE:
@@ -1185,8 +1189,6 @@ static int snapshot_status(struct dm_tar
break;
}

- up_write(&snap->lock);
-
return 0;
}