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.
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Davidlohr Bueso <d...@stgolabs.net>
Reported-by: Michael Kerrisk <mtk.manpa...@gmail.com>
Signed-off-by: Darren Hart <dvh...@linux.intel.com>
---
kernel/futex.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/futex.c b/kernel/futex.c
index 684d754..3c8c6d6 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -3046,7 +3046,8 @@ 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;
}
--
2.1.4
--
Darren Hart
Intel Open Source Technology Center
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