Re: [PATCH] perfcounters: fix "perf counters kills oprofile" bug

[Ingo Molnar]

* Mike Galbraith <efault@xxxxxx> wrote:

> Impact: fix "perf counters kills oprofile" bug
> 
> Both oprofile and perfcounters register an NMI die handler, but only one
> can handle the NMI.  Conveniently, oprofile unregisters it's notifier
> when not actively in use, so setting it's notifier priority higher than
> perfcounter's allows oprofile to borrow the NMI for the duration of it's
> run.  Tested/works both as module and built-in.
> 
> While testing, I found that if kerneltop was generating NMIs at very
> high frequency, the kernel may panic when oprofile registered it's
> handler.  This turned out to be because oprofile registers it's handler
> before reset_value has been allocated, so if an NMI comes in while it's
> still setting up, kabOom.  Rather than try more invasive changes, I
> followed the lead of other places in op_model_ppro.c, and simply
> returned in that highly unlikely event.  (debug warnings attached)

applied to tip:perfcounters/core, thanks Mike!

> I can break this into two patches if you prefer, but since the panic was 
> initiated by borrowing the active NMI, I figured they belong together.

No need, it's fine this way. Note that there's two commits from you: i 
applied your earier fix of this already, and now i did a delta patch of the 
other bug you found. The delta patch i have applied is below.

Thanks,

	Ingo

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