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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 9 Apr 2020 14:17:39 -0700
Message-ID: <CAHk-=wgh4zts+3hdkGzHLJ6pBGumcJ=23gRbMfubDrLstis2Bg@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:     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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On Thu, Apr 9, 2020 at 2:03 PM Eric W. Biederman <ebiederm@xmission.com> wrote:
>
> 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.

So Eric, I'm now going to stop wasting my time on arguing with you.

Since both you and Bernd claimed to be too busy to even bother testing
that thing, I just built it and booted it.

And guess what? That thing makes your non-deadlock thing go away.

So it's _literally_ that simple.

Now, does it make the tests "pass"? No.

Because the "vmaccess" test fails because the open() now fails -
because we simply don't wait for that dead thread any more, so the
/proc/<pid>/mem thing doesn't exist.

And for the same reason that "attach" test now no longer returns
EAGAIN, it just attaches to the remaining execlp thing instead.

So I'm not just good at "spotting odd corner cases". I told you why
that bogus deadlock of yours failed - the execve was pointlessly
waiting for a dead thread that had marked itself ptraced, and nobody
was reaping it.

And it appears you were too lazy to even try it out.

Yes, that whole "notify_dead" count vs "tsk->exit_state" test is
fundamentally racy. But that race happens to be irrelevant for the
test case in question.

So until you can actually add something to the discussion, I'm done
with this thread.

           Linus