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dm snapshot: fix register_snapshot deadlock

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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>
This commit is contained in:
Mikulas Patocka
2008-10-30 13:33:12 +00:00
committed by Alasdair G Kergon
parent b34578a484
commit 60c856c8e2
1 changed files with 9 additions and 7 deletions
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16
drivers/md/dm-snap.c
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@@ -229,19 +229,21 @@ static void __insert_origin(struct origin *o)
*/ */
static int register_snapshot(struct dm_snapshot *snap) static int register_snapshot(struct dm_snapshot *snap)
{ {
struct origin *o; struct origin *o, *new_o;
struct block_device *bdev = snap->origin->bdev; struct block_device *bdev = snap->origin->bdev;
new_o = kmalloc(sizeof(*new_o), GFP_KERNEL);
if (!new_o)
return -ENOMEM;
down_write(&_origins_lock); down_write(&_origins_lock);
o = __lookup_origin(bdev); o = __lookup_origin(bdev);
if (!o) { if (o)
kfree(new_o);
else {
/* New origin */ /* New origin */
o = kmalloc(sizeof(*o), GFP_KERNEL); o = new_o;
if (!o) {
up_write(&_origins_lock);
return -ENOMEM;
}
/* Initialise the struct */ /* Initialise the struct */
INIT_LIST_HEAD(&o->snapshots); INIT_LIST_HEAD(&o->snapshots);