rbd: retrieve and check lock owner twice before blocklisting

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: [email protected] # f38cb9d9c204: rbd: make get_lock_owner_info() return a single locker or NULL
Cc: [email protected] # 8ff2c64c9765: rbd: harden get_lock_owner_info() a bit
Cc: [email protected]
Signed-off-by: Ilya Dryomov <[email protected]>
Reviewed-by: Dongsheng Yang <[email protected]>

0 files changed, 0 insertions, 0 deletions