locks: wake any locks blocked on request before deadlock check

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>

diff --git a/fs/locks.c b/fs/locks.c
index eaa1cfaf73b08c8fda256ea57ab816dcc4985217..71d0c6c2aac5ccde4d69cdf7396fbdbdfb40c3e6 100644 (file)
--- 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,