[PATCH v3] locks: wake any locks blocked on request before deadlock check

[Jeff Layton <jlayton@kernel.org>]

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.

While we remove the request from the blocked_lock_hash prior to
reattempting to acquire it, any locks that are blocked on that request
will still be present in the hash and will still have their fl_blocker
pointer set to the current request.

This causes posix_locks_deadlock to find a deadlock dependency chain
when it shouldn't, as a lock request cannot block itself.

We are going to end up waking all of those blocked locks anyway when we
go to reinsert the request back into the blocked_lock_hash, so just do
it prior to checking for deadlocks. This ensures that any lock blocked
on the current request will no longer be part of any blocked request
chain.

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 | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/locks.c b/fs/locks.c
index eaa1cfaf73b0..71d0c6c2aac5 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1160,6 +1160,11 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
 			 */
 			error = -EDEADLK;
 			spin_lock(&blocked_lock_lock);
+			/*
+			 * Ensure that we don't find any locks blocked on this
+			 * request during deadlock detection.
+			 */
+			__locks_wake_up_blocks(request);
 			if (likely(!posix_locks_deadlock(request, fl))) {
 				error = FILE_LOCK_DEFERRED;
 				__locks_insert_block(fl, request,
-- 
2.20.1