Re: perf: perf_fuzzer crashes on Pentium 4 systems

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Wed, Apr 03, 2019 at 10:59:32AM -0400, Vince Weaver wrote:
> 
> so moving this to its own thread.
> 
> There was a two-part question asked.
> 	1. Can the perf-fuzzer crash a Pentium 4 system
> 	2. Does anyone care anymore?
> 
> The answer to #1 turns out to be "yes"
> I'm not sure about #2 (but it's telling my p4 test system hadn't been 
> turned on in over 3 years).
> 
> In any case the perf_fuzzer can crash my p4 system within an hour or so.  
> The debugging from this isn't great, I forget what the preferred debug 
> things to enable in the kernel hacking menu are.
> 
> Here is one crash that just happened:
> 
> The instruction at RIP is unhelpfully
> 	./arch/x86/include/asm/processor.h:400
> which is
> 	DECLARE_PER_CPU_FIRST(union irq_stack_union, irq_stack_union) __visible;
> 
> Though looking at the assembly it looks like
> 	p4_pmu_enable_event() is called with NULL as the paramater.
>

Interesting! I'll look more carefully at evening. As far as I remember we
rely on active_mask bit set completely, not sure how it could happen that
we get nil here. Thanks for pointing!