The following commit has been merged into the locking/urgent branch of tip:

Commit-ID: 4fbf5d6837bf81fd7a27d771358f4ee6c4f243f8 Gitweb: https://git.kernel.org/tip/4fbf5d6837bf81fd7a27d771358f4ee6c4f243f8 Author: Thomas Gleixner tglx@linutronix.de AuthorDate: Thu, 22 Apr 2021 21:44:18 +02:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Thu, 06 May 2021 20:12:40 +02:00

Revert 337f13046ff0 ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op")

The FUTEX_WAIT operand has historically a relative timeout which means that the clock id is irrelevant as relative timeouts on CLOCK_REALTIME are not subject to wall clock changes and therefore are mapped by the kernel to CLOCK_MONOTONIC for simplicity.

If a caller would set FUTEX_CLOCK_REALTIME for FUTEX_WAIT the timeout is still treated relative vs. CLOCK_MONOTONIC and then the wait arms that timeout based on CLOCK_REALTIME which is broken and obviously has never been used or even tested.

Reject any attempt to use FUTEX_CLOCK_REALTIME with FUTEX_WAIT again.

The desired functionality can be achieved with FUTEX_WAIT_BITSET and a FUTEX_BITSET_MATCH_ANY argument.

Fixes: 337f13046ff0 ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op") Signed-off-by: Thomas Gleixner tglx@linutronix.de Acked-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20210422194704.834797921@linutronix.de

--- kernel/futex.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c index c98b825..4740200 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -3710,8 +3710,7 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,

if (op & FUTEX_CLOCK_REALTIME) { flags |= FLAGS_CLOCKRT; - if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \ - cmd != FUTEX_WAIT_REQUEUE_PI) + if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI) return -ENOSYS; }