linux-kernel - [tip:locking/core] futex: Avoid freeing an active timer

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Message-ID: <tip-97181f9bd57405b879403763284537e27d46963d@git.kernel.org>
Date:   Fri, 14 Apr 2017 02:30:28 -0700
From:   tip-bot for Thomas Gleixner <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     peterz@...radead.org, alexander.levin@...izon.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, linux-kernel@...r.kernel.org, hpa@...or.com
Subject: [tip:locking/core] futex: Avoid freeing an active timer

Commit-ID:  97181f9bd57405b879403763284537e27d46963d
Gitweb:     http://git.kernel.org/tip/97181f9bd57405b879403763284537e27d46963d
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Mon, 10 Apr 2017 18:03:36 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 14 Apr 2017 10:29:53 +0200

futex: Avoid freeing an active timer

Alexander reported a hrtimer debug_object splat:

  ODEBUG: free active (active state 0) object type: hrtimer hint: hrtimer_wakeup (kernel/time/hrtimer.c:1423)

  debug_object_free (lib/debugobjects.c:603)
  destroy_hrtimer_on_stack (kernel/time/hrtimer.c:427)
  futex_lock_pi (kernel/futex.c:2740)
  do_futex (kernel/futex.c:3399)
  SyS_futex (kernel/futex.c:3447 kernel/futex.c:3415)
  do_syscall_64 (arch/x86/entry/common.c:284)
  entry_SYSCALL64_slow_path (arch/x86/entry/entry_64.S:249)

Which was caused by commit:

  cfafcd117da0 ("futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock()")

... losing the hrtimer_cancel() in the shuffle. Where previously the
hrtimer_cancel() was done by rt_mutex_slowlock() we now need to do it
manually.

Reported-by: Alexander Levin <alexander.levin@...izon.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Fixes: cfafcd117da0 ("futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock()")
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1704101802370.2906@nanos
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/futex.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index c3eebcd..7ac1676 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2736,8 +2736,10 @@ out_unlock_put_key:
 out_put_key:
 	put_futex_key(&q.key);
 out:
-	if (to)
+	if (to) {
+		hrtimer_cancel(&to->timer);
 		destroy_hrtimer_on_stack(&to->timer);
+	}
 	return ret != -EINTR ? ret : -ERESTARTNOINTR;
 
 uaddr_faulted: