From 88a57e387cf0b967fc84a6632086e76b9d6c3431 Mon Sep 17 00:00:00 2001 From: Ilya Dryomov Date: Fri, 13 Mar 2020 11:20:51 +0100 Subject: [PATCH] rbd: avoid a deadlock on header_rwsem when flushing notifies [ 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 Reviewed-by: Jason Dillaman Signed-off-by: Sasha Levin --- 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 a673157..bab9c54 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; @@ -7028,6 +7038,8 @@ 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: rbd_dev->image_format = 0; @@ -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) -- 2.7.4