linux-kernel - [PATCH 5.0 045/146] locks: wake any locks blocked on request before deadlock check

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Date:   Mon,  1 Apr 2019 19:00:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andreas Schneider <asn@...hat.com>,
        Neil Brown <neilb@...e.com>, Jeff Layton <jlayton@...nel.org>
Subject: [PATCH 5.0 045/146] locks: wake any locks blocked on request before deadlock check

5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jeff Layton <jlayton@...nel.org>

commit 945ab8f6de94430c23a82f3cf2e3f6d6f2945ff7 upstream.

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@...r.kernel.org
Reported-by: Andreas Schneider <asn@...hat.com>
Signed-off-by: Neil Brown <neilb@...e.com>
Signed-off-by: Jeff Layton <jlayton@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/locks.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1160,6 +1160,11 @@ static int posix_lock_inode(struct inode
 			 */
 			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,