linux-kernel - Re: [patch 00/12] futex: Cure robust/PI futex exit races

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Message-ID: <87o8xm95rt.fsf@oldenburg2.str.redhat.com>
Date:   Fri, 08 Nov 2019 08:38:46 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Darren Hart <darren@...art.com>,
        Yi Wang <wang.yi59@....com.cn>,
        Yang Tao <yang.tao172@....com.cn>,
        Oleg Nesterov <oleg@...hat.com>,
        Carlos O'Donell <carlos@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [patch 00/12] futex: Cure robust/PI futex exit races

* Florian Weimer:

> * Florian Weimer:
>
>> * Thomas Gleixner:
>>
>>> The series is also available from git:
>>>
>>>   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git WIP.locking/futex
>>
>> I ran the glibc upstream test suite (which has some robust futex tests)
>> against b21be7e942b49168ee15a75cbc49fbfdeb1e6a97 on x86-64, both native
>> and 32-bit/i386 compat mode.
>>
>> compat mode seems broken, nptl/tst-thread-affinity-pthread fails.  This
>> is probably *not* due to
>> <https://bugzilla.kernel.org/show_bug.cgi?id=154011> because the failure
>> is non-sporadic, but reliable fails for thread 253:
>>
>> info: Detected CPU set size (in bits): 225
>> info: Maximum test CPU: 255
>> error: pthread_create for thread 253 failed: Resource temporarily unavailable
>>
>> I'm running this on a large box as root, so ulimits etc. do not apply.
>>
>> I did not see this failure with the x86-64 test.
>>
>> You should be able to reproduce with (assuming you've got a multilib gcc):
>>
>> git clone git://sourceware.org/git/glibc.git git
>> mkdir build
>> cd build
>> ../git/configure --prefix=/usr CC="gcc -m32" CXX="g++ -m32" --build=i686-linux
>> make -j`nproc`
>> make test t=nptl/tst-thread-affinity-pthread
>
> Sorry, I realized that I didn't actually verify that this is a
> regression caused by your patches.  Maybe I can do that tomorrow.

Confirmed as a regression caused by the patches.  Depending on the
nature of the bug, you need a machine which has or pretends to have many
CPUs (this one has 256 CPUs).

Please let me know if you need more information.

Thanks,
Florian