Messages in this thread | | | Date | Wed, 09 Sep 2009 10:40:35 +0800 | From | Li Zefan <> | Subject | Re: [PATCH 1/2] tracing: Add sysctl to enable/disable tracing on oops |
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>>>>>>> Currently we always disable tracing on oops, and this patch >>>>>>> adds a sysctl so one can choose to enable it. >>>>>> Hmm, we already have a way to enable it. >>>>>> >>>>>> # echo 1 > /debug/tracing/tracing_on >>>>>> >>>>> What I want is a way to not disable it when an oops happened. :) >>>>> >>>> Ah, I misunderstood. May I ask a silly question? >>>> >>>> Why? >>>> >>> Otherwise we won't get trace output from trae_crash_kexec if >>> crash_kexec() is not called by panic(). For example: >>> >>> oops_begin() >>> ->trace_off() >>> ->panic_on_oops >>> ->kexec_should_crash() >>> ->crash_kexec() >> OK, but I'm not exactly sure what you final goal is here. To have a >> something to search for in the ring buffer after the crash? Maybe >> instead we can add a "trace_oops" event? Just put it before the >> tracing_off call. > > I have another silly question. > Why should we call tracing_off() in oops_enter()? >
I guess it's because trace outputs generated during oops can overwrite/mess up those generated before oops?
It was added by this commit, but I can't find trace_printk_on_oops.
commit bdff78707f3ce47e891f3201c9666122a70556ce Author: Thomas Gleixner <tglx@linutronix.de> Date: Fri Jul 24 15:30:45 2009 -0400
trace: stop tracer in oops_enter()
If trace_printk_on_oops is set we lose interesting trace information when the tracer is enabled across oops handling and printing. We want the trace which might give us information _WHY_ we oopsed.
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