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@xxxxxxxxxxxxxxx Reported-by: Andreas Schneider <asn@xxxxxxxxxx> Signed-off-by: Neil Brown <neilb@xxxxxxxx> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> --- 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. + */ + if (block_fl == caller_fl) + return 0; + if (posix_same_owner(caller_fl, block_fl)) return 1; } -- 2.20.1
