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

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Message-Id: <20190201161227.GG3770@osiris>
Date:   Fri, 1 Feb 2019 17:12:27 +0100
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     Sebastian Sewior <bigeasy@...utronix.de>
Cc:     Thomas Gleixner <tglx@...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 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.