linux-kernel - [patch 2/6] futex: Do not apply time namespace adjustment on FUTEX_LOCK

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Date:   Thu, 22 Apr 2021 21:44:19 +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>,
        Andrei Vagin <avagin@...il.com>, stable@...r.kernel.org,
        Darren Hart <dvhart@...radead.org>,
        Kurt Kanzenbach <kurt@...utronix.de>
Subject: [patch 2/6] futex: Do not apply time namespace adjustment on FUTEX_LOCK_PI

FUTEX_LOCK_PI does not require to have the FUTEX_CLOCK_REALTIME bit set
because it has been using CLOCK_REALTIME based absolute timeouts
forever. Due to that, the time namespace adjustment which is applied when
FUTEX_CLOCK_REALTIME is not set, will wrongly take place for FUTEX_LOCK_PI
and wreckage the timeout.

Exclude it from that procedure.

Fixes: c2f7d08cccf4 ("futex: Adjust absolute futex timeouts with per time namespace offset")
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Andrei Vagin <avagin@...il.com>
Cc: stable@...r.kernel.org
---
 kernel/futex.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -3781,7 +3781,7 @@ SYSCALL_DEFINE6(futex, u32 __user *, uad
 		t = timespec64_to_ktime(ts);
 		if (cmd == FUTEX_WAIT)
 			t = ktime_add_safe(ktime_get(), t);
-		else if (!(op & FUTEX_CLOCK_REALTIME))
+		else if (cmd != FUTEX_LOCK_PI && !(op & FUTEX_CLOCK_REALTIME))
 			t = timens_ktime_to_host(CLOCK_MONOTONIC, t);
 		tp = &t;
 	}
@@ -3975,7 +3975,7 @@ SYSCALL_DEFINE6(futex_time32, u32 __user
 		t = timespec64_to_ktime(ts);
 		if (cmd == FUTEX_WAIT)
 			t = ktime_add_safe(ktime_get(), t);
-		else if (!(op & FUTEX_CLOCK_REALTIME))
+		else if (cmd != FUTEX_LOCK_PI && !(op & FUTEX_CLOCK_REALTIME))
 			t = timens_ktime_to_host(CLOCK_MONOTONIC, t);
 		tp = &t;
 	}