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

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Message-ID: <AM6PR03MB5170660DA597EAAAC0AC1B5BE4DF0@AM6PR03MB5170.eurprd03.prod.outlook.com>
Date:   Sat, 11 Apr 2020 21:15:11 +0200
From:   Bernd Edlinger <bernd.edlinger@...mail.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Waiman Long <longman@...hat.com>,
        Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexey Gladkov <gladkov.alexey@...il.com>
Subject: Re: [GIT PULL] Please pull proc and exec work for 5.7-rc1



On 4/11/20 8:29 PM, Linus Torvalds wrote:
> On Sat, Apr 11, 2020 at 11:21 AM Oleg Nesterov <oleg@...hat.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
>