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

[Kohli, Gaurav]

Hi John, Ingo

As still we are seeing race between do_task_stat and do_exit of task, 
Can't we have to
put more strict check in case, if stack pointer is NULL in below code :

ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ if (permitted && (task->flags & PF_DUMPCORE)) {
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ eip = KSTK_EIP(task);
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ esp = KSTK_ESP(task);
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ }

Regards
Gaurav


On 1/9/2018 7:03 PM, Kohli, Gaurav wrote:
> 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(
> 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
>
> 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
>
>
> -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation 
> Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation 
> Collaborative Project.

-- Qualcomm India Private Limited, on behalf of Qualcomm Innovation 
Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation 
Collaborative Project.