Messages in this thread | | | Subject | Re: [PATCH] [2/2] Don't complain about disabled irqs when the system has paniced | From | Peter Zijlstra <> | Date | Tue, 02 Sep 2008 16:45:17 +0200 |
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On Tue, 2008-09-02 at 16:40 +0200, Andi Kleen wrote: > On Tue, Sep 02, 2008 at 04:28:03PM +0200, Peter Zijlstra wrote: > > On Tue, 2008-09-02 at 15:49 +0200, Andi Kleen wrote: > > > panic calls smp_send_stop which eventually calls smp_call_function_*. > > > smp_call_function warns about disabled interrupts. But it's legal > > > to call panic in this case. When this happens panic() prints > > > several ugly backtraces. So don't check for disabled interrupts > > > in panic state. > > > > While it might be legal for panic to be called from such contexts, I > > understand those warnings are there to warn of deadlocks. > > > > So with the below patch you allow panic to deadlock if I understand > > things correctly. > > Please describe the deadlock exactly. I don't think it can deadlock > in this case.
Then why are those warnings there? The deadlock is for the CSD_FLAG_WAIT case, which can always happen due to the static csd data fallback.
The deadlock scenario is long the lines of two such smp_call_function*() both under irq disabled calling each other with CSD_FLAG_WAIT set. Neither remote cpu will handle the IPI due to irqs being disabled, so we'll wait at-infinitum for completion.
> Besides do you prefer to not allow panic from interrupts/machine > checks etc. anymore?
However did I imply that, I just said your fix looked iffy.
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