Messages in this thread | | | Date | Thu, 9 Apr 2020 11:40:16 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH] ARM64: fixed dump_backtrace() when task running on another cpu |
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Hi,
On Thu, Apr 09, 2020 at 05:38:16PM +0800, Wang Qing wrote: > We cannot get FP and PC when the task is running on another CPU, > task->thread.cpu_context is the last time the task was switched out, > it's better to give a reminder than to provide wrong information. > > Signed-off-by: Wang Qing <wangqing@vivo.com>
Are you seeing this happen anywhere in particular today?
> --- > arch/arm64/kernel/traps.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c > index cf402be..c04e3e8 100644 > --- a/arch/arm64/kernel/traps.c > +++ b/arch/arm64/kernel/traps.c > @@ -106,6 +106,14 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk) > start_backtrace(&frame, > (unsigned long)__builtin_frame_address(0), > (unsigned long)dump_backtrace); > + } else if (tsk->on_cpu) { > + /* > + * The task is running in another cpu, so the call stack > + * is changing and we cannot get it. > + */ > + pr_warn("tsk: %s is running in CPU%d, Don't call trace!\n", > + tsk->comm, tsk->cpu);
I believe that we can race with a concurrent write to tsk->cpu in both cases above. We could use READ_ONCE() to get a snapshot, but we can still race and miss cases where the task was runnning as we backtrace it.
Thanks, Mark.
> + return; > } else { > /* > * task blocked in __switch_to > -- > 2.7.4 >
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