linux-kernel - Re: WARN_ON_ONCE(!new_owner) within wake_futex

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Message-ID: <alpine.DEB.2.21.1902012258290.8200@nanos.tec.linutronix.de>
Date:   Fri, 1 Feb 2019 22:59:08 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Heiko Carstens <heiko.carstens@...ibm.com>
cc:     Sebastian Sewior <bigeasy@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-s390@...r.kernel.org,
        Stefan Liebler <stli@...ux.ibm.com>
Subject: Re: WARN_ON_ONCE(!new_owner) within wake_futex_pi() triggerede

On Fri, 1 Feb 2019, Heiko Carstens wrote:
> On Thu, Jan 31, 2019 at 06:06:53PM +0100, Sebastian Sewior wrote:
> > On 2019-01-31 17:52:28 [+0100], Heiko Carstens wrote:
> > > ...nevertheless Stefan and I looked through the lovely disassembly of
> > > _pthread_mutex_lock_full() to verify if the compiler barriers are
> > > actually doing what they are supposed to do. The generated code
> > > however does look correct.
> > > So, it must be something different.
> > 
> > would it make sense to use one locking function instead all three (lock,
> > try-lock, timed) in the test case to figure out if this is related to
> > one of the locking function?
> 
> I tried all three variants, but it seems to be close to impossible to
> re-create then. I had a single fail when using only the trylock
> variant, but I wouldn't say that means anything.
> 
> Only if all three variants run in parallel it seems to be quite
> reliably reproducible, even though sometimes it still takes an hour.

Were you able to capture a trace with the last set of additional trace
printks?

Thanks,

	tglx