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

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Message-ID: <AM6PR03MB51708CF53D8A02086427DAC2E4AC0@AM6PR03MB5170.eurprd03.prod.outlook.com>
Date:   Tue, 28 Apr 2020 04:56:48 +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 4/12/20 10:14 PM, Linus Torvalds wrote:
> On Sun, Apr 12, 2020 at 12:51 PM Oleg Nesterov <oleg@...hat.com> wrote:
>>
>> To be honest, I don't understand it... OK, suppose that the main thread
>> M execs and zap_other_threads() finds a single (and alive) sub-thread T,
>> sig->notify_count = 1.
>>
>> If T is traced, then ->notify_count won't be decremented until the tracer
>> reaps this task, so we have the same problem.
> 
> Right you are.
> 
> I was hoping to avoid the "move notify_count update", but you're
> right, the threads that do get properly killed will never get to that
> point, so now the live ones that we're waiting for will just hit the
> same issue that the dead ones did.
> 
> Goot catch. So the optimistic simplification doesn't work.
> 
>>> You do say in that old patch that we can't just share the signal
>>> state, but I wonder how true that is.
>>
>> We can share sighand_struct with TASK_ZOMBIE's. The problem is that
>> we can not unshare ->sighand until they go away, execing thread and
>> zombies must use the same sighand->siglock to serialize the access to
>> ->thread_head/etc.
> 
> Yeah, they'll still touch the lock, and maybe look at it, but it's not
> like they'll be changing any state.
> 
>> but see above, I don't think this makes any sense.
> 
> Yeah, I think your patch is better since my simplification doesn't work.
> 

Ping...
was this resolved meanwhile?


Thanks
Bernd.

>              Linus
>