Commit 0e4e1de5 authored by Ilya Dryomov's avatar Ilya Dryomov
Browse files

rbd: avoid a deadlock on header_rwsem when flushing notifies 



rbd_unregister_watch() flushes notifies and therefore cannot be called
under header_rwsem because a header update notify takes header_rwsem to
synchronize with "rbd map".  If mapping an image fails after the watch
is established and a header update notify sneaks in, we deadlock when
erroring out from rbd_dev_image_probe().

Move watch registration and unregistration out of the critical section.
The only reason they were put there was to make header_rwsem management
slightly more obvious.

Fixes: 811c6688 ("rbd: fix rbd map vs notify races")
Signed-off-by: default avatarIlya Dryomov <idryomov@gmail.com>
Reviewed-by: default avatarJason Dillaman <dillaman@redhat.com>
parent 8f3d9f35

drivers/block/rbd.c

+13 −4
Original line number Diff line number Diff line
@@ -4527,6 +4527,10 @@ static void cancel_tasks_sync(struct rbd_device *rbd_dev) 
	cancel_work_sync(&rbd_dev->unlock_work);

}



/*

 * header_rwsem must not be held to avoid a deadlock with

 * rbd_dev_refresh() when flushing notifies.

 */

static void rbd_unregister_watch(struct rbd_device *rbd_dev)

{

	cancel_tasks_sync(rbd_dev);
@@ -6907,6 +6911,9 @@ static void rbd_dev_image_release(struct rbd_device *rbd_dev) 
 * device.  If this image is the one being mapped (i.e., not a

 * parent), initiate a watch on its header object before using that

 * object to get detailed information about the rbd image.

 *

 * On success, returns with header_rwsem held for write if called

 * with @depth == 0.

 */

static int rbd_dev_image_probe(struct rbd_device *rbd_dev, int depth)

{
@@ -6936,6 +6943,9 @@ static int rbd_dev_image_probe(struct rbd_device *rbd_dev, int depth) 
		}

	}



	if (!depth)

		down_write(&rbd_dev->header_rwsem);



	ret = rbd_dev_header_info(rbd_dev);

	if (ret) {

		if (ret == -ENOENT && !need_watch)
@@ -6987,6 +6997,8 @@ static int rbd_dev_image_probe(struct rbd_device *rbd_dev, int depth) 
err_out_probe:

	rbd_dev_unprobe(rbd_dev);

err_out_watch:

	if (!depth)

		up_write(&rbd_dev->header_rwsem);

	if (need_watch)

		rbd_unregister_watch(rbd_dev);

err_out_format:
@@ -7050,12 +7062,9 @@ static ssize_t do_rbd_add(struct bus_type *bus, 
		goto err_out_rbd_dev;

	}



	down_write(&rbd_dev->header_rwsem);

	rc = rbd_dev_image_probe(rbd_dev, 0);

	if (rc < 0) {

		up_write(&rbd_dev->header_rwsem);

	if (rc < 0)

		goto err_out_rbd_dev;

	}



	if (rbd_dev->opts->alloc_size > rbd_dev->layout.object_size) {

		rbd_warn(rbd_dev, "alloc_size adjusted to %u",

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