Re: [PATCH 1/3] perf_event: fix race inperf_swevent_get_recursion_context()

[Peter Zijlstra]

On Tue, 2010-01-19 at 15:36 +0800, Xiao Guangrong wrote:
> Hi Peter,
> 
> Peter Zijlstra wrote:
> > On Mon, 2010-01-18 at 21:42 +0800, Xiao Guangrong wrote:
> >> It only disable preemption in perf_swevent_get_recursion_context()
> >> it can't avoid race of hard-irq and NMI
> >>
> >> In this patch, we use atomic operation to avoid it and reduce
> >> cpu_ctx->recursion size, it also make this patch no need diable
> >> preemption
> > 
> > Uhm why?
> > 
> > This patch looks terminally broken
> 
> Please see my explanation in another mail:
> http://lkml.org/lkml/2010/1/18/501

Still its not going to happen, we need those 4 recursion contexts.
Otherwise we could not receive a software event from an IRQ while we are
processing a software event from process context, etc.

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