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Subject: Re: Query: Crash is coming during /prod/PID/stat and do_exit of same
 task
To: John Ogness <john.ogness@linutronix.de>
Cc: peterz@infradead.org, mingo@kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org
References: <36ea8b88-4786-dbb2-6b89-15f9801e9c86@codeaurora.org>
 <87zi5fxu4g.fsf@linutronix.de>
From: "Kohli, Gaurav" <gkohli@codeaurora.org>
Message-ID: <959b7b1e-3f93-5792-c613-d23b21c46246@codeaurora.org>
Date: Mon, 15 Jan 2018 18:00:14 +0530
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On 1/15/2018 4:32 PM, John Ogness wrote:

> Hello Gaurav.
>
> On 2018-01-09, Kohli, Gaurav <gkohli@codeaurora.org> 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:
>>
>> Below is the crash trace:
>> 49750.534377] Kernel BUG at ffffff8e7a4c53a8 [verbose debug info
>> unavailable]
>> [49750.534394] task: ffffffe7b4475580 task.stack: ffffffe7a5f0c000
>> [49750.534400] PC is at do_task_stat+0x740/0x908
>> [49750.534402] LR is at do_task_stat+0xa4/0x908
>> [49750.534403] pc : [<ffffff8e7a4c53a8>] lr : [<ffffff8e7a4c4d0c>]
>> pstate: 80400145
>> [49750.534404] sp : ffffffe7a5f0fbd0
>>
>> and here is stack trace on that core:
>>
>> -000|user_stack_pointer(inline)
>> -000|do_task_stat(
>>      |    m = 0xFFFFFFE7A5CD7380,
>>      |    ns = 0xFFFFFF8E7C43C748,
>>      |  ?,
>>      |    task = 0xFFFFFFE80D8C2280,
>>      |  ?)
>>      |  tty_pgrp = 0
>>      |  ppid = 2084696064
>>      |  sid = 0
>>      |  mm = 0xFFFFFFE7B4424140
>>      |  tcomm = (84, 9, 71, 122, 142, 255, 255, 255, 48, 253, 240, 165,
>> 231, 255, 255, 255)
>>      |  flags = 18446743969119403392
>> -001|proc_tgid_stat(
>>      |    m = 0xFFFFFFE7A5CD7380,
>>      |  ?,
>>
>> Below are task stats which shows , process completed the do_exit call:
>> struct task_struct.flags -x 0xFFFFFFE80D8C2280
>>    flags = 0x40870c
>>
>> crash_64> struct task_struct.exit_code -x 0xFFFFFFE80D8C2280
>>    exit_code = 0x6
>>
>>     struct task_struct.state -x 0xFFFFFFE80D8C2280
>>    state = 0x40
> I am confused why this task is in the TASK_PARKED state. What kind of
> task is this?

Hi John,

This is android HAL layer service and also before bug, i am seeing lot of service exited in logs also,
although not seeing for this pid 6807

.452202:   <2> init: starting service 'limits-hal-1-0'...

  49749.460039:   <2> init: property_set("ro.boottime.limits-hal-1-0", "61591320967789") failed: property already set

  49749.607496:   <6> sh (2422): drop_caches: 3

  49750.281635:   <6> sh (2422): drop_caches: 3

  49750.533853:   <2> init: Untracked pid 6811 exited with status 0

And why it is parked , that is not clear as state is already updated of task.

Regards

Gaurav

>
>> In our build both patches are there ,
>> fs/proc: report eip/esp in /prod/PID/stat for coredumping
>>
>> and also  task.state has already set PF_DUMPCORE as it got the sigabrt
>> signal.
> John Ogness
>
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