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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 9 Apr 2020 09:15:37 -0700
Message-ID: <CAHk-=wjhAvv6s_7OVeZJiHaY7bBrHyiPTkSpq-TLr6qxYqxUUw@mail.gmail.com>
Subject: Re: [GIT PULL] Please pull proc and exec work for 5.7-rc1
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Waiman Long <longman@redhat.com>, Ingo Molnar <mingo@kernel.org>,
        Will Deacon <will@kernel.org>,
        Bernd Edlinger <bernd.edlinger@hotmail.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Alexey Gladkov <gladkov.alexey@gmail.com>
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On Thu, Apr 9, 2020 at 8:01 AM Eric W. Biederman <ebiederm@xmission.com> wrote:
>
> When a thread going about it's ordinary business receives the SIGKILL
> from de_thread the thread changes course and finds it's way to do_exit.
> In do_exit the thread calls ptrace_event(PTRACE_EVENT_EXIT, ...) and
> blocks waiting for the tracer to let it continue.

Hah.

That code isn't _supposed_ to block.

may_ptrace_stop() is supposed to stop the blocking exactly so that it
doesn't deadlock.

I wonder why that doesn't work..

[ Goes and look ]

Oh. I see.

That ptrace_may_stop() only ever considered core-dumping, not execve().

But if _that_ is the reason for the deadlock, then it's trivially fixed.

Famous last words..

             Linus