linux-kernel - [tip:locking/core] futex: Allow FUTEX_CLOCK_REALTIME with FUTEX

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Message-ID: <tip-337f13046ff03717a9e99675284a817527440a49@git.kernel.org>
Date:	Sun, 20 Dec 2015 05:20:23 -0800
From:	tip-bot for Darren Hart <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	peterz@...radead.org, dave@...olabs.net,
	linux-kernel@...r.kernel.org, dvhart@...ux.intel.com,
	mingo@...nel.org, tglx@...utronix.de, mtk.manpages@...il.com,
	hpa@...or.com
Subject: [tip:locking/core] futex:
  Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op

Commit-ID:  337f13046ff03717a9e99675284a817527440a49
Gitweb:     http://git.kernel.org/tip/337f13046ff03717a9e99675284a817527440a49
Author:     Darren Hart <dvhart@...ux.intel.com>
AuthorDate: Fri, 18 Dec 2015 13:36:37 -0800
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Sun, 20 Dec 2015 12:43:25 +0100

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@...il.com>
Signed-off-by: Darren Hart <dvhart@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Davidlohr Bueso <dave@...olabs.net>
Link: http://lkml.kernel.org/r/9f3bdc116d79d23f5ee72ceb9a2a857f5ff8fa29.1450474525.git.dvhart@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/futex.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 461d438..8a310e2 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -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;
 	}
 
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