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

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Message-ID: <alpine.DEB.2.11.1510161234340.3960@nanos>
Date:	Fri, 16 Oct 2015 12:35:23 +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)

On Fri, 16 Oct 2015, Heiko Carstens wrote:
> On Fri, Oct 16, 2015 at 12:21:51PM +0200, Thomas Gleixner wrote:
> > Heiko,
> > 
> > On Thu, 15 Oct 2015, Heiko Carstens wrote:
> > >   /* We wait for half a second.  */
> > >   ts.tv_nsec += 500000000;
> > >   if (ts.tv_nsec >= 1000000000)
> > >     {
> > >       ++ts.tv_sec;
> > >       ts.tv_nsec -= 1000000000;
> > >     }
> > > 
> > >   ret = syscall (__NR_futex, &futex_word, op, expected, ts, NULL, FUTEX_BITSET_MATCH_ANY);
> > 
> > If you actually hand in a pointer to 'ts' then the program works as
> > expected even with the commit in question applied.
> 
> Yes, sorry about that! I was just about to write that this should have
> been &ts on x86. Since x86 seems to pass also structures >8 bytes by
> value.
> 
> However on s390 it is passed by reference. So even it I change ts to &ts,
> it will hang as I described.
> 
> So you are saying this works on x86 and it must be some s390 specific bug?

Looks like. I have no idea why that would break on s390. Did you try
to revert the commit on top of tree?

Thanks,

	tglx
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