linux-kernel - Re: commit cfafcd117 "futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock()" causes glibc nptl/tst-robustpi8 failure

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Date:   Wed, 17 May 2017 19:50:31 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Markus Trippelsdorf <markus@...ppelsdorf.de>,
        linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Torvald Riegel <triegel@...hat.com>
Subject: Re: commit cfafcd117 "futex: Rework futex_lock_pi() to use
 rt_mutex_*_proxy_lock()" causes glibc nptl/tst-robustpi8 failure

On 05/17/2017 07:36 PM, Markus Trippelsdorf wrote:
> Since:
> commit cfafcd117da0216520568c195cb2f6cd1980c4bb
> Author: Peter Zijlstra <peterz@...radead.org>
> Date:   Wed Mar 22 11:35:58 2017 +0100
> 
>     futex: Rework futex_lock_pi() to use rt_mutex_*_proxy_lock()
> 
> glibc's nptl/tst-robustpi8 testcase fails:
> 
> glibc-build % ./nptl/tst-robustpi8
> tst-robustpi8: ../nptl/pthread_mutex_lock.c:424: __pthread_mutex_lock_full: Assertion `INTERNAL_SYSCALL_ERRNO (e, __err) != ESRCH || !robust' failed.
> 
> pthread_mutex_lock.c:
> 415             if (INTERNAL_SYSCALL_ERROR_P (e, __err)
> 416                 && (INTERNAL_SYSCALL_ERRNO (e, __err) == ESRCH
> 417                     || INTERNAL_SYSCALL_ERRNO (e, __err) == EDEADLK))
> 418               {
> 419                 assert (INTERNAL_SYSCALL_ERRNO (e, __err) != EDEADLK
> 420                         || (kind != PTHREAD_MUTEX_ERRORCHECK_NP
> 421                             && kind != PTHREAD_MUTEX_RECURSIVE_NP));
> 422                 /* ESRCH can happen only for non-robust PI mutexes where
> 423                    the owner of the lock died.  */
> 424                 assert (INTERNAL_SYSCALL_ERRNO (e, __err) != ESRCH || !robust);
> 
> During bisection the commit above hangs the machine when I run the
> testcase.
> 
> See: https://sourceware.org/bugzilla/show_bug.cgi?id=21487

Markus, could you confirm that it is chocking on the EAGAIN failure?  Or
is it something else?

What is userspace supposed to do with the error code?

Thanks,
Florian