The patch title
   locks: ignore same lock in blocked_lock_hash

is a bit misleading the lock isn't in the hash, but it is linked from
something that is.  Maybe

   locks: ignore same lock in posix_locks_deadlock()

??

On Sat, Mar 23 2019, Jeff Layton wrote:

> Andreas reported that he was seeing the tdbtorture test fail in
> some cases with -EDEADLCK when it wasn't before. Some debugging
> showed that deadlock detection was sometimes discovering the
> caller's lock request itself in a dependency chain.
>
> If posix_locks_deadlock() fails to find a deadlock, the caller_fl
> will be passed to __locks_insert_block(), and this wakes up all
> locks that are blocked on caller_fl, clearing the fl_blocker link.
>
> So if posix_locks_deadlock() finds caller_fl while searching for
> a deadlock, it can be sure that link in the cycle is about to be
> broken and it need not treat it as the cause of a deadlock.
>
> URL: https://bugzilla.kernel.org/show_bug.cgi?id=202975
> Fixes: 5946c4319ebb ("fs/locks: allow a lock request to block other requests.")
> Cc: stable@vger.kernel.org
> Reported-by: Andreas Schneider <asn@redhat.com>
> Signed-off-by: Neil Brown <neilb@suse.com>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  fs/locks.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/fs/locks.c b/fs/locks.c
> index eaa1cfaf73b0..a939a274dc71 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -1023,6 +1023,19 @@ static int posix_locks_deadlock(struct file_lock *caller_fl,
>  	while ((block_fl = what_owner_is_waiting_for(block_fl))) {
>  		if (i++ > MAX_DEADLK_ITERATIONS)
>  			return 0;
> +
> +		/*
> +		 * It's possible that we're retrying this lock request after
> +		 * another task is has blocked on it. A lock request can't
> +		 * block itself, and any locks that are blocked on it will
> +		 * also be awoken soon (and have their fl_blocker pointer
> +		 * cleared). Any dependency chain that contains the request
> +		 * itself is therefore about to be broken, so we can safely
> +		 * ignore it.

That first sentence isn't working for me .... maybe remove the "is" ??

Thanks,
NeilBrown


> +		 */
> +		if (block_fl == caller_fl)
> +			return 0;
> +
>  		if (posix_same_owner(caller_fl, block_fl))
>  			return 1;
>  	}
> -- 
> 2.20.1