Re: Query: Crash is coming during /prod/PID/stat and do_exit of same task

[John Ogness <john.ogness@linutronix.de>]

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?

> 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