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

Bernd Edlinger
2020-04-11T19:15:22Z

On 4/11/20 8:29 PM, Linus Torvalds wrote:
> On Sat, Apr 11, 2020 at 11:21 AM Oleg Nesterov <oleg@redhat.com> wrote:
>>
>> On 04/09, Linus Torvalds wrote:
>>>
>>> (1) have execve() not wait for dead threads while holding the cred
>>> mutex
>>
>> This is what I tried to do 3 years ago, see
>
> Well, you did it differently - by moving the "wait for dead threads"
> logic to after releasing the lock.
>
> My simpler patch was lazier - just don't wait for dead threads at all,
> since they are dead and not interesting.

But won't the dead thread's lifetime overlap the new thread's lifetime
from the tracer's POV?

Bernd.

>
> Because even if it's Easter weekend, those threads are not coming back
> to life ;)
>
> You do say in that old patch that we can't just share the signal
> state, but I wonder how true that is. Sharing it with a TASK_ZOMBIE
> doesn't seem all that problematic to me. The only thing that can do is
> getting reaped by a later wait.
>
> That said, I actually am starting to think that maybe execve() should
> just try to reap those threads instead, and avoid the whole issue that
> way. Basically my "option (2)" thing.
>
> Sure, that's basically stealing them from the parent, but 'execve()'
> really is special wrt threads, and the parent still has the execve()
> thread itself. And it's not so different from SIGKILL, which also
> forcibly breaks off any ptracer etc without anybody being able to say
> anything about it.
>
> Linus
>