linux-kernel - [tip: locking/core] futex: Prepare futex_lock

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Date:   Wed, 23 Jun 2021 08:19:07 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Kurt Kanzenbach <kurt@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: locking/core] futex: Prepare futex_lock_pi() for runtime clock
 selection

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

Commit-ID:     e112c41341c03d9224a9fc522bdb3539bc849b56
Gitweb:        https://git.kernel.org/tip/e112c41341c03d9224a9fc522bdb3539bc849b56
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Thu, 22 Apr 2021 21:44:22 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 22 Jun 2021 16:42:08 +02:00

futex: Prepare futex_lock_pi() for runtime clock selection

futex_lock_pi() is the only futex operation which cannot select the clock
for timeouts (CLOCK_MONOTONIC/CLOCK_REALTIME). That's inconsistent and
there is no particular reason why this cannot be supported.

This was overlooked when CLOCK_REALTIME_FLAG was introduced and
unfortunately not reported when the inconsistency was discovered in glibc.

Prepare the function and enforce the CLOCK_REALTIME_FLAG on FUTEX_LOCK_PI
so that a new FUTEX_LOCK_PI2 can implement it correctly.

Reported-by: Kurt Kanzenbach <kurt@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/r/20210422194705.338657741@linutronix.de
---
 kernel/futex.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 08008c2..f820439 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2783,7 +2783,7 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
 	if (refill_pi_state_cache())
 		return -ENOMEM;
 
-	to = futex_setup_timer(time, &timeout, FLAGS_CLOCKRT, 0);
+	to = futex_setup_timer(time, &timeout, flags, 0);
 
 retry:
 	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
@@ -3739,6 +3739,7 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
 	case FUTEX_WAKE_OP:
 		return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
 	case FUTEX_LOCK_PI:
+		flags |= FLAGS_CLOCKRT;
 		return futex_lock_pi(uaddr, flags, timeout, 0);
 	case FUTEX_UNLOCK_PI:
 		return futex_unlock_pi(uaddr, flags);