Commit 337f1304 authored Dec 18, 2015 by Darren Hart Committed by Thomas Gleixner Dec 20, 2015

futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op



While reviewing Michael Kerrisk's recent futex manpage update, I noticed
that we allow the FUTEX_CLOCK_REALTIME flag for FUTEX_WAIT_BITSET but
not for FUTEX_WAIT.

FUTEX_WAIT is treated as a simple version for FUTEX_WAIT_BITSET
internally (with a bitmask of FUTEX_BITSET_MATCH_ANY). As such, I cannot
come up with a reason for this exclusion for FUTEX_WAIT.

This change does modify the behavior of the futex syscall, changing a
call with FUTEX_WAIT | FUTEX_CLOCK_REALTIME from returning -ENOSYS, to be
equivalent to FUTEX_WAIT_BITSET | FUTEX_CLOCK_REALTIME with a bitset of
FUTEX_BITSET_MATCH_ANY.

Reported-by: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Link: http://lkml.kernel.org/r/9f3bdc116d79d23f5ee72ceb9a2a857f5ff8fa29.1450474525.git.dvhart@linux.intel.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

parent 885c2cb7

kernel/futex.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -3084,7 +3084,8 @@ 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_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
		if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \
		cmd != FUTEX_WAIT_REQUEUE_PI)
		return -ENOSYS;
		}