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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Bernd Edlinger <bernd.edlinger@hotmail.de>,
        Waiman Long <longman@redhat.com>,
        Ingo Molnar <mingo@kernel.org>, Will Deacon <will@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Alexey Gladkov <gladkov.alexey@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>
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Date:   Thu, 09 Apr 2020 16:00:43 -0500
In-Reply-To: <CAHk-=whJttTNFQn1fMYp91LZ90iHE7B2THZ8NjQ7fBwmWX9k6w@mail.gmail.com>
        (Linus Torvalds's message of "Thu, 9 Apr 2020 13:04:34 -0700")
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Subject: Re: [GIT PULL] Please pull proc and exec work for 5.7-rc1
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Linus Torvalds <torvalds@linux-foundation.org> writes:

> On Thu, Apr 9, 2020 at 12:57 PM Bernd Edlinger
> <bernd.edlinger@hotmail.de> wrote:
>>
>> The use case where this may happen with strace
>> when you call strace with lots of -p <pid> arguments,
>> and one of them is a bomb. strace stuck.
>
> Yeah, so from a convenience angle I do agree that it would be nicer to
> just not count dead threads.
>
> You can test that by just moving the
>
>                 /* Don't bother with already dead threads */
>                 if (t->exit_state)
>                         continue;
>
> test in zap_other_threads() to above the
>
>                 count++;
>
> line instead.

That looks like a legitimate race, and something worth addressing.  It
doesn't look like t->exit_state has siglock protection so I don't think
testing it under siglock would fix that race.  But something like that
certainly should.

But no.  While you are goind a good job at spotting odd corner
cases that need to be fixed.  This also is not the cause of the
deadlock.  It is nothing that subtle.

Eric