From: Ilya Dryomov idryomov@gmail.com
[ Upstream commit 0e4e1de5b63fa423b13593337a27fd2d2b0bcf77 ]
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: 811c66887746 ("rbd: fix rbd map vs notify races") Signed-off-by: Ilya Dryomov idryomov@gmail.com Reviewed-by: Jason Dillaman dillaman@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/block/rbd.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index a67315786db47..bab9c546ba334 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -4636,6 +4636,10 @@ 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); @@ -6942,6 +6946,9 @@ 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) { @@ -6974,6 +6981,9 @@ 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) goto err_out_watch; @@ -7027,6 +7037,8 @@ 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 (!depth) rbd_unregister_watch(rbd_dev); err_out_format: @@ -7085,12 +7097,9 @@ 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 we are mapping a snapshot it must be marked read-only */ if (rbd_dev->spec->snap_id != CEPH_NOSNAP)