lkml.org 
[lkml]   [2018]   [Mar]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] arm64: avoid race condition issue in dump_backtrace
Hi Ji Zhang,

On Thu, Mar 22, 2018 at 11:06:00AM +0800, Ji Zhang wrote:
> When we dump the backtrace of some specific task, there is a potential race
> condition due to the task may be running on other cores if SMP enabled.
> That is because for current implementation, if the task is not the current
> task, we will get the registers used for unwind from cpu_context saved in
> thread_info, which is the snapshot before context switch, but if the task
> is running on other cores, the registers and the content of stack are
> changed.
> This may cause that we get the wrong backtrace or incomplete backtrace or
> even crash the kernel.
> To avoid this case, do not dump the backtrace of the tasks which are
> running on other cores.
> This patch cannot solve the issue completely but can shrink the window of
> race condition.
>
> Signed-off-by: Ji Zhang <ji.zhang@mediatek.com>
> ---
> arch/arm64/kernel/traps.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index eb2d151..95749364 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -113,6 +113,9 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
> if (tsk == current) {
> frame.fp = (unsigned long)__builtin_frame_address(0);
> frame.pc = (unsigned long)dump_backtrace;
> + else if (tsk->state == TASK_RUNNING) {

Missing closing brace. Does this build?

> + pr_notice("Do not dump other running tasks\n");
> + return;
> } else {
> /*
> * task blocked in __switch_to

baruch

--
http://baruch.siach.name/blog/ ~. .~ Tk Open Systems
=}------------------------------------------------ooO--U--Ooo------------{=
- baruch@tkos.co.il - tel: +972.2.679.5364, http://www.tkos.co.il -

\
 
 \ /
  Last update: 2018-03-22 05:57    [W:0.175 / U:0.624 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site