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

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Message-Id: <20190129102409.GB26906@osiris>
Date:   Tue, 29 Jan 2019 11:24:09 +0100
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     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>,
        Sebastian Sewior <bigeasy@...utronix.de>
Subject: Re: WARN_ON_ONCE(!new_owner) within wake_futex_pi() triggered

On Tue, Jan 29, 2019 at 10:45:44AM +0100, Thomas Gleixner wrote:
> On Tue, 29 Jan 2019, Heiko Carstens wrote:
> > On Mon, Jan 28, 2019 at 04:53:19PM +0100, Thomas Gleixner wrote:
> > > Patch below cures that.
> > 
> > With your patch the kernel warning doesn't occur anymore. So if this
> > is supposed to be the fix feel free to add:
> 
> Yes, it's supposed to be the fix.
> > 
> > However now I see every now and then the following failure from the
> > same test case:
> > 
> > tst-robustpi8: ../nptl/pthread_mutex_lock.c:425: __pthread_mutex_lock_full: Assertion `INTERNAL_SYSCALL_ERRNO (e, __err) != ESRCH || !robust' failed.
> > 
> > 		/* ESRCH can happen only for non-robust PI mutexes where
> > 		   the owner of the lock died.	*/
> > 		assert (INTERNAL_SYSCALL_ERRNO (e, __err) != ESRCH || !robust);
> > 
> > I just verified that this happened also without your patch, I just
> > didn't see it since I started my tests with panic_on_warn=1 and the
> > warning triggered always earlier.
> > So, this seems to be something different.
> 
> Moo. I ran the test loop all night (simply because I forgot to stop it) and
> of course this does not trigger here. Could you try to gather a bit more
> information with lightweight tracing?

Yes, sure. However ;) I reproduced the above with v5.0-rc4 + your
patch. And now I am trying to reproduce with linux-next 20190129 +
your patch and it doesn't trigger. Did I miss a patch which is only in
linux-next which could fix this?