linux-kernel - Re: [PATCH 20/24] task_diag: Only add VMAs for thread

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Date:	Wed, 15 Jul 2015 15:31:07 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Ahern <dsahern@...il.com>
Cc:	Andrey Vagin <avagin@...nvz.org>, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Roger Luethi <rl@...lgate.ch>, Arnd Bergmann <arnd@...db.de>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Pavel Odintsov <pavel.odintsov@...il.com>
Subject: Re: [PATCH 20/24] task_diag: Only add VMAs for thread_group leader

On 07/14, David Ahern wrote:
>
> On 7/14/15 1:47 PM, Oleg Nesterov wrote:
>>>
>>>   	if (show_flags & TASK_DIAG_SHOW_VMA) {
>>> +		/* if the request is to dump all threads of all processes
>>> +		 * only show VMAs for group leader.
>>> +		 */
>>> +		if (req->dump_strategy == TASK_DIAG_DUMP_ALL_THREAD &&
>>> +		    !thread_group_leader(tsk))
>>> +			goto done;
>>> +
>>
>> This doesn't look right, group leader can be a zombie with ->mm == NULL,
>
> Seriously?

Yes, the main thread can do sys_exit() / pthread_exit(), although this
is not that common.

> I'll find some way to track whether VMAs have been dumped for
> a pid.

In case I confused you, the thread_group_leader() check and "goto done"
above are fine, just you can't trust tsk->mm, so

>>>   		if (i >= n)
>>>   			err = fill_vma(tsk, skb, cb, &progress, show_flags);
>>
>> so this probably needs something like find_lock_task_mm().
>
> ok.

Yes, you just need to (try) find a subthread with ->mm != NULL if !tsk->mm,
find_lock_task_mm() can help.

Oleg.

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