linux-kernel - Re: Query: Crash is coming during /prod/PID/stat and do

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Message-ID: <9982db93-e392-f6da-e70b-d38d818cd4ff@codeaurora.org>
Date:   Tue, 16 Jan 2018 15:14:59 +0530
From:   "Kohli, Gaurav" <gkohli@...eaurora.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: Query: Crash is coming during /prod/PID/stat and do_exit of same
 task

On 1/16/2018 12:50 PM, Alexey Dobriyan wrote:

> On Tue, Jan 16, 2018 at 11:06:47AM +0530, Kohli, Gaurav wrote:
>> On 1/10/2018 10:50 AM, Alexey Dobriyan wrote:
>>
>>>> We are seeing crash in do_task_stat while accessing stack pointer, It
>>>> seems same task has already completed do_exit call.
>>>> So it seems a race between them:
>>> Please, post exact kernel version and struct task_struct::usage if you
>>> still have that kernel core (or even full task_struct)
>> Hi Alexey,
>>
>> We are working on 4.9.65 and Please find below usage value and other task_struct value,
>> please let me know if some other data required as well.
> Kernel stacks live their own lives nowadays, the code needs try_get_task_stack().
>
Hi Alexey,

Yes , agree we have to put some check like below

   if (permitted && (task->flags & PF_DUMPCORE) && try_get_task_stack(task)) {

                         eip = KSTK_EIP(task);

                         esp = KSTK_ESP(task);

                 }

Or instead of this also , can't we check whether task is in exiting path or not by checking some flags like PF_EXITING.

Regards

Gaurav

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