linux-kernel - Re: futex timeout not working? (bisected)

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Message-ID: <alpine.DEB.2.11.1510161443520.4212@nanos>
Date:	Fri, 16 Oct 2015 14:45:37 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
cc:	Stefan Liebler <stli@...ux.vnet.ibm.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: futex timeout not working? (bisected)

Heiko,

On Fri, 16 Oct 2015, Thomas Gleixner wrote:
> On Fri, 16 Oct 2015, Heiko Carstens wrote:
> > Adding the patch below also "fixes" this. Right now I don't see why this
> > could architecture specific. Hmm.
> > 
> > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> > index 3739ac6aa473..75771b15647c 100644
> > --- a/kernel/time/timekeeping.c
> > +++ b/kernel/time/timekeeping.c
> > @@ -1835,7 +1835,7 @@ void update_wall_time(void)
> >  	 * memcpy under the tk_core.seq against one before we start
> >  	 * updating.
> >  	 */
> > -	timekeeping_update(tk, clock_set);
> > +	timekeeping_update(tk, clock_set | TK_CLOCK_WAS_SET);
> >  	memcpy(real_tk, tk, sizeof(*tk));
> >  	/* The memcpy must come last. Do not put anything here! */
> >  	write_seqcount_end(&tk_core.seq);
> 
> Well, the latter is incrementing the sequence count on every wall time
> update.
> 
> The question is why the hrtimer code is not seeing that the clock was
> set at some point during boot.
> 
> Lemme dig into that.

The only point I found which does not update the sequence count is
timekeeping_init().

Does the patch below fix your issue?

Thanks,

	tglx

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

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 3739ac6aa473..44d2cc0436f4 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1251,7 +1251,7 @@ void __init timekeeping_init(void)
 	set_normalized_timespec64(&tmp, -boot.tv_sec, -boot.tv_nsec);
 	tk_set_wall_to_mono(tk, tmp);
 
-	timekeeping_update(tk, TK_MIRROR);
+	timekeeping_update(tk, TK_MIRROR | TK_CLOCK_WAS_SET);
 
 	write_seqcount_end(&tk_core.seq);
 	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
--
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