Messages in this thread | | | Date | Mon, 29 Jul 2019 22:15:06 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] tracing: Prevent RCU EQS breakage in preemptirq events |
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On Tue, 30 Jul 2019 11:00:42 +0900 Eiichi Tsukata <devel@etsukata.com> wrote:
> Thanks for comments. > > On 2019/07/30 0:21, Steven Rostedt wrote: > > On Mon, 29 Jul 2019 10:07:34 +0900 > > Eiichi Tsukata <devel@etsukata.com> wrote: > > > >> If context tracking is enabled, causing page fault in preemptirq > >> irq_enable or irq_disable events triggers the following RCU EQS warning. > >> > >> Reproducer: > >> > >> // CONFIG_PREEMPTIRQ_EVENTS=y > >> // CONFIG_CONTEXT_TRACKING=y > >> // CONFIG_RCU_EQS_DEBUG=y > >> # echo 1 > events/preemptirq/irq_disable/enable > >> # echo 1 > options/userstacktrace > > > > So the problem is only with userstacktrace enabled? > > It can happen when tracing code causes page fault in preemptirq events. > For example, the following perf command also hit the warning: > > # perf record -e 'preemptirq:irq_enable' -g ls
Again,
That's not a irq trace event issue, that's a stack trace issue.
> > > >> > >> __visible void trace_hardirqs_on_caller(unsigned long caller_addr) > >> { > >> + enum ctx_state prev_state; > >> + > >> if (this_cpu_read(tracing_irq_cpu)) { > >> - if (!in_nmi()) > >> + if (!in_nmi()) { > > > > This is a very high fast path (for tracing irqs off and such). Instead > > of adding a check here for a case that is seldom used (userstacktrace > > and tracing irqs on/off). Move this to surround the userstack trace > > code. > > > > -- Steve > > If the problem was only with userstacktrace, it will be reasonable to > surround only the userstack unwinder. But the situation is similar to > the previous "tracing vs CR2" case. As Peter taught me in > https://lore.kernel.org/lkml/20190708074823.GV3402@hirez.programming.kicks-ass.net/ > there are some other codes likely to to user access. > So I surround preemptirq events earlier.
I disagree. The issue is with the attached callbacks that call something (a stack unwinder) that can fault.
This is called whenever irqs are disabled. I say we surround the culprit (the stack unwinder or stack trace) and not punish the irq enable/disable events.
So NAK on this patch.
-- Steve
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