Commit 60c856c8 authored Oct 30, 2008 by Mikulas Patocka Committed by Alasdair G Kergon Oct 30, 2008

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>

parent b34578a4

drivers/md/dm-snap.c

+9 −7

Original line number	Diff line number	Diff line
		@@ -229,19 +229,21 @@ static void __insert_origin(struct origin *o)
		*/
		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);