dm snapshot: only take lock for statustype info not table
Mikulas Patocka [Thu, 10 Dec 2009 23:51:53 +0000 (23:51 +0000)]
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.

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

index 3a3ba46..d135212 100644 (file)
@@ -1152,10 +1152,11 @@ static int snapshot_status(struct dm_target *ti, status_type_t type,
        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_target *ti, status_type_t type,
                        else
                                DMEMIT("Unknown");
                }
+
+               up_write(&snap->lock);
+
                break;
 
        case STATUSTYPE_TABLE:
@@ -1185,8 +1189,6 @@ static int snapshot_status(struct dm_target *ti, status_type_t type,
                break;
        }
 
-       up_write(&snap->lock);
-
        return 0;
 }