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rbd: retrieve and check lock owner twice before blocklisting
commit 5881590 upstream. An attempt to acquire exclusive lock can race with the current lock owner closing the image: 1. lock is held by client123, rbd_lock() returns -EBUSY 2. get_lock_owner_info() returns client123 instance details 3. client123 closes the image, lock is released 4. find_watcher() returns 0 as there is no matching watcher anymore 5. client123 instance gets erroneously blocklisted Particularly impacted is mirror snapshot scheduler in snapshot-based mirroring since it happens to open and close images a lot (images are opened only for as long as it takes to take the next mirror snapshot, the same client instance is used for all images). To reduce the potential for erroneous blocklisting, retrieve the lock owner again after find_watcher() returns 0. If it's still there, make sure it matches the previously detected lock owner. Cc: stable@vger.kernel.org # f38cb9d: rbd: make get_lock_owner_info() return a single locker or NULL Cc: stable@vger.kernel.org # 8ff2c64: rbd: harden get_lock_owner_info() a bit Cc: stable@vger.kernel.org Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Reviewed-by: Dongsheng Yang <dongsheng.yang@easystack.cn> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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