linux-kernel - [patch 5/6] futex: Prepare futex_lock

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Date:   Thu, 22 Apr 2021 21:44:22 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Adhemerval Zanella <adhemerval.zanella@...aro.org>,
        Lukasz Majewski <lukma@...x.de>,
        Florian Weimer <fweimer@...hat.com>,
        Carlos O'Donell <carlos@...hat.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Ingo Molnar <mingo@...nel.org>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Darren Hart <dvhart@...radead.org>,
        Andrei Vagin <avagin@...il.com>
Subject: [patch 5/6] 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>
---
 kernel/futex.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2786,7 +2786,7 @@ static int futex_lock_pi(u32 __user *uad
 	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);
@@ -3711,7 +3711,7 @@ long do_futex(u32 __user *uaddr, int op,
 
 	if (op & FUTEX_CLOCK_REALTIME) {
 		flags |= FLAGS_CLOCKRT;
-		if (cmd != FUTEX_WAIT_BITSET &&	cmd != FUTEX_WAIT_REQUEUE_PI)
+		if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
 			return -ENOSYS;
 	}
 
@@ -3743,6 +3743,7 @@ long do_futex(u32 __user *uaddr, int op,
 	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);