linux-kernel - Re: [PATCH -v6 11/13] futex: Rework futex_lock_pi() to use rt_mutex_*_proxy

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Message-ID: <alpine.DEB.2.20.1704101802370.2906@nanos>
Date:   Mon, 10 Apr 2017 18:03:36 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     alexander.levin@...izon.com
cc:     Peter Zijlstra <peterz@...radead.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "juri.lelli@....com" <juri.lelli@....com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "xlpang@...hat.com" <xlpang@...hat.com>,
        "bigeasy@...utronix.de" <bigeasy@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mathieu.desnoyers@...icios.com" <mathieu.desnoyers@...icios.com>,
        "jdesfossez@...icios.com" <jdesfossez@...icios.com>,
        "bristot@...hat.com" <bristot@...hat.com>,
        "dvhart@...radead.org" <dvhart@...radead.org>
Subject: Re: [PATCH -v6 11/13] futex: Rework futex_lock_pi() to use
 rt_mutex_*_proxy_lock()

On Mon, 10 Apr 2017, alexander.levin@...izon.com wrote:
> On Wed, Mar 22, 2017 at 11:35:58AM +0100, Peter Zijlstra wrote:
> > By changing futex_lock_pi() to use rt_mutex_*_proxy_lock() we arrive
> > at a point where all wait_list modifications are done under both
> > hb->lock and wait_lock.
> [...]
> 
> Hey Peter,
> 
> I'm seeing the following, which seems to be related to this patch:
> 
> [   21.762875] ODEBUG: free active (active state 0) object type: hrtimer hint: hrtimer_wakeup (kernel/time/hrtimer.c:1423)

> [   21.788050] debug_object_free (lib/debugobjects.c:603)
> [   21.791105] destroy_hrtimer_on_stack (kernel/time/hrtimer.c:427)
> [   21.791746] futex_lock_pi (kernel/futex.c:2740)
> [   21.800721] do_futex (kernel/futex.c:3399)
> [   21.818395] SyS_futex (kernel/futex.c:3447 kernel/futex.c:3415)
> [   21.822260] do_syscall_64 (arch/x86/entry/common.c:284)
> [   21.827328] entry_SYSCALL64_slow_path (arch/x86/entry/entry_64.S:249)

Yep, that rework dropped the hrtimer cancel. Fix below.

Thanks,

	tglx

8<------------------------

diff --git a/kernel/futex.c b/kernel/futex.c
index c3eebcdac206..7ac167683c9f 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2736,8 +2736,10 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
 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: