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

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Message-ID: <AM6PR03MB5170147F396B3F40D093C499E4C70@AM6PR03MB5170.eurprd03.prod.outlook.com>
Date:   Fri, 3 Apr 2020 18:36:37 +0200
From:   Bernd Edlinger <bernd.edlinger@...mail.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        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 4/3/20 6:23 PM, Linus Torvalds wrote:
> On Fri, Apr 3, 2020 at 8:09 AM Bernd Edlinger <bernd.edlinger@...mail.de> wrote:
>>
>> On 4/2/20 9:04 PM, Linus Torvalds wrote:
>>> In fact, then you could drop the
>>>
>>>                         mutex_unlock(&tsk->signal->exec_update_mutex);
>>>
>>> in the error case of exec_mmap(), because now the error handling in
>>> free_bprm() would do the cleanup automatically.
>>>
>>
>> The error handling is sometimes called when the exec_update_mutex is
>> not taken, in fact even de_thread not called.
> 
> But that's the whole point of the flag. Make the flag be about "do I
> hold the mutex", and then the error handling does the right thing
> regardless.
> 
>> Can you say how you would suggest that to be done?
> 
> I think the easiest thing to do to explain is to just write the patch.
> 
> This is entirely untested, but see what the difference is? I make the
> flag be about exactly where I take the lock, not about some "I have
> called exec_mmap".
> 
> Which means that now exec_mmap() doesn't even need to unlock it in the
> error case, because the unlocking will happen properly in the
> bprm_exit regardless.
> 
> This makes that unconditional unlocking logic much more obvious.
> 
> That said, Eric says he can make it all properly static so that it
> doesn't need that kind of dynamic "if (x) unlock()" logic at all,
> which is much better.
> 
> So this patch is not for consumption, it's purely for "look, something
> like this"
> 

Works for me.  But I also want to wait for Eric, I am curious.
I have a lot of time.


Bernd.

>               Linus
>