Re: [GIT PULL] Please pull proc and exec work for 5.7-rc1

[Eric W. Biederman]

Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes:

> On Thu, Apr 9, 2020 at 12:57 PM Bernd Edlinger
> <bernd.edlinger@xxxxxxxxxx> 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