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futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op

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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 <[email protected]>
Signed-off-by: Darren Hart <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Link: http://lkml.kernel.org/r/9f3bdc116d79d23f5ee72ceb9a2a857f5ff8fa29.1450474525.git.dvhart@linux.intel.com
Signed-off-by: Thomas Gleixner <[email protected]>
This commit is contained in:
Darren Hart authored and Thomas Gleixner committed 2015-12-20 12:43:25 +01:00
1 parent 885c2cb770
commit 337f13046f
1 file changed
+2 -1
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kernel/futex.c
+2 -1
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@@ -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;
}