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

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HI ,

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

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.

Regards
Gaurav


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