dm snapshot: fix register_snapshot deadlock
register_snapshot() performs a GFP_KERNEL allocation while holding
_origins_lock for write, but that could write out dirty pages onto a
device that attempts to acquire _origins_lock for read, resulting in
deadlock.
So move the allocation up before taking the lock.
This path is not performance-critical, so it doesn't matter that we
allocate memory and free it if we find that we won't need it.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index b2d9d1a..746603b 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -229,19 +229,21 @@
*/
static int register_snapshot(struct dm_snapshot *snap)
{
- struct origin *o;
+ struct origin *o, *new_o;
struct block_device *bdev = snap->origin->bdev;
+ new_o = kmalloc(sizeof(*new_o), GFP_KERNEL);
+ if (!new_o)
+ return -ENOMEM;
+
down_write(&_origins_lock);
o = __lookup_origin(bdev);
- if (!o) {
+ if (o)
+ kfree(new_o);
+ else {
/* New origin */
- o = kmalloc(sizeof(*o), GFP_KERNEL);
- if (!o) {
- up_write(&_origins_lock);
- return -ENOMEM;
- }
+ o = new_o;
/* Initialise the struct */
INIT_LIST_HEAD(&o->snapshots);