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SubjectRe: [PATCH] arm64: break while loop if task had been rescheduled
On 2019-05-24 18:41, Mark Rutland wrote:
> On Tue, May 21, 2019 at 05:20:04PM +0800, Tengfei Fan wrote:
>> While printing a task's backtrace and this task isn't
>> current task, it is possible that task's fp and fp+8
>> have the same value, so cannot break the while loop.
>> This can break while loop if this task had been
>> rescheduled during print this task's backtrace.
>
> There are a few cases where backtracing can get stuck in an infinite
> loop. I'd attempted to address that more generally in my
> arm64/robust-stacktrace branch [1].
>
> Looking at tsk->state here is inherently racy, and doesn't solve the
> general case, so I'd prefer to avoid that.
>
> Do my patches help you here? If so, I'm happy to rebase those to
> v5.2-rc1 and repost.

I think your arm64/robust-stacktrace branch [1] can cover my issue,
please
rebase and reposet

Thanks,
Tengfei Fan

>
> Thanks,
> Mark.
>
> [1]
> https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/robust-stacktrace
>
>>
>> Signed-off-by: Tengfei Fan <tengfeif@codeaurora.org>
>> ---
>> arch/arm64/kernel/traps.c | 23 +++++++++++++++++++++++
>> 1 file changed, 23 insertions(+)
>>
>> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
>> index 2975598..9df6e02 100644
>> --- a/arch/arm64/kernel/traps.c
>> +++ b/arch/arm64/kernel/traps.c
>> @@ -103,6 +103,9 @@ void dump_backtrace(struct pt_regs *regs, struct
>> task_struct *tsk)
>> {
>> struct stackframe frame;
>> int skip = 0;
>> + long cur_state = 0;
>> + unsigned long cur_sp = 0;
>> + unsigned long cur_fp = 0;
>>
>> pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
>>
>> @@ -127,6 +130,9 @@ void dump_backtrace(struct pt_regs *regs, struct
>> task_struct *tsk)
>> */
>> frame.fp = thread_saved_fp(tsk);
>> frame.pc = thread_saved_pc(tsk);
>> + cur_state = tsk->state;
>> + cur_sp = thread_saved_sp(tsk);
>> + cur_fp = frame.fp;
>> }
>> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>> frame.graph = 0;
>> @@ -134,6 +140,23 @@ void dump_backtrace(struct pt_regs *regs, struct
>> task_struct *tsk)
>>
>> printk("Call trace:\n");
>> do {
>> + if (tsk != current && (cur_state != tsk->state
>> + /*
>> + * We would not be printing backtrace for the task
>> + * that has changed state from uninterruptible to
>> + * running before hitting the do-while loop but after
>> + * saving the current state. If task is in running
>> + * state before saving the state, then we may print
>> + * wrong call trace or end up in infinite while loop
>> + * if *(fp) and *(fp+8) are same. While the situation
>> + * will stop print when that task schedule out.
>> + */
>> + || cur_sp != thread_saved_sp(tsk)
>> + || cur_fp != thread_saved_fp(tsk))) {
>> + printk("The task:%s had been rescheduled!\n",
>> + tsk->comm);
>> + break;
>> + }
>> /* skip until specified stack frame */
>> if (!skip) {
>> dump_backtrace_entry(frame.pc);
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
>> Forum,
>> a Linux Foundation Collaborative Project
>>

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