Messages in this thread | | | Date | Thu, 30 May 2019 10:41:11 +0800 | From | tengfeif@codeauro ... | Subject | Re: [PATCH] arm64: break while loop if task had been rescheduled |
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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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