rbd: take header_rwsem in rbd_dev_refresh() only when updating
commit 0b207d02 upstream. rbd_dev_refresh() has been holding header_rwsem across header and parent info read-in unnecessarily for ages. With commit 870611e4 ("rbd: get snapshot context after exclusive lock is ensured to be held"), the potential for deadlocks became much more real owning to a) header_rwsem now nesting inside lock_rwsem and b) rw_semaphores not allowing new readers after a writer is registered. For example, assuming that I/O request 1, I/O request 2 and header read-in request all target the same OSD: 1. I/O request 1 comes in and gets submitted 2. watch error occurs 3. rbd_watch_errcb() takes lock_rwsem for write, clears owner_cid and releases lock_rwsem 4. after reestablishing the watch, rbd_reregister_watch() calls rbd_dev_refresh() which takes header_rwsem for write and submits a header read-in request 5. I/O request 2 comes in: after taking lock_rwsem for read in __rbd_img_handle_request(), it blocks trying to take header_rwsem for read in rbd_img_object_requests() 6. another watch error occurs 7. rbd_watch_errcb() blocks trying to take lock_rwsem for write 8. I/O request 1 completion is received by the messenger but can't be processed because lock_rwsem won't be granted anymore 9. header read-in request completion can't be received, let alone processed, because the messenger is stranded Change rbd_dev_refresh() to take header_rwsem only for actually updating rbd_dev->header. Header and parent info read-in don't need any locking. Cc: stable@vger.kernel.org # 0b035401: rbd: move rbd_dev_refresh() definition Cc: stable@vger.kernel.org # 510a7330: rbd: decouple header read-in from updating rbd_dev->header Cc: stable@vger.kernel.org # c1031177: rbd: decouple parent info read-in from updating rbd_dev Cc: stable@vger.kernel.org Fixes: 870611e4 ("rbd: get snapshot context after exclusive lock is ensured to be held") Signed-off-by:Ilya Dryomov <idryomov@gmail.com> Reviewed-by:
Dongsheng Yang <dongsheng.yang@easystack.cn> Signed-off-by:
Sasha Levin <sashal@kernel.org>
parent
698039a4
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