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

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Date:   Fri, 8 Nov 2019 10:18:08 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Florian Weimer <fweimer@...hat.com>
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

On Fri, 8 Nov 2019, Florian Weimer wrote:
> * Florian Weimer:
> > * Florian Weimer:
> >> 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).

Sure I can do that, but I completely fail to see how that's a
regression.

Unpatched 5.4-rc6:

FAIL: nptl/tst-thread-affinity-pthread
original exit status 1
info: Detected CPU set size (in bits): 225
info: Maximum test CPU: 255
error: pthread_create for thread 253 failed: Resource temporarily unavailable

TBH, the futex changes have absolutely nothing to do with that resource
fail.

Thanks,

	tglx