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

[John Ogness]

Hello Gaurav.

On 2018-01-09, Kohli, Gaurav <gkohli@xxxxxxxxxxxxxx> 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(
> ÂÂÂ |ÂÂÂ m = 0xFFFFFFE7A5CD7380,
> ÂÂÂ |ÂÂÂ ns = 0xFFFFFF8E7C43C748,
> ÂÂÂ |Â ?,
> ÂÂÂ |ÂÂÂ task = 0xFFFFFFE80D8C2280,
> ÂÂÂ |Â ?)
> ÂÂÂ |Â tty_pgrp = 0
> ÂÂÂ |Â ppid = 2084696064
> ÂÂÂ |Â sid = 0
> ÂÂÂ |Â mm = 0xFFFFFFE7B4424140
> ÂÂÂ |Â tcomm = (84, 9, 71, 122, 142, 255, 255, 255, 48, 253, 240, 165,
> 231, 255, 255, 255)
> ÂÂÂ |Â flags = 18446743969119403392
> -001|proc_tgid_stat(
> ÂÂÂ |ÂÂÂ m = 0xFFFFFFE7A5CD7380,
> ÂÂÂ |Â ?,
>
> Below are task stats which shows , process completed the do_exit call:
> struct task_struct.flags -x 0xFFFFFFE80D8C2280
> Â flags = 0x40870c
>
> crash_64> struct task_struct.exit_code -x 0xFFFFFFE80D8C2280
> Â exit_code = 0x6
>
> ÂÂ struct task_struct.state -x 0xFFFFFFE80D8C2280
> Â 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