Re: perf: fuzzer triggered trouble on AMD, maybe ibs related

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Oct 22, 2015 at 12:46:53PM -0400, Vince Weaver wrote:
> Hello
> 
> I've been busy but finally had a chance to run perf_fuzzer on current git.
> I am running on an AMD A10 system (my traditional Haswell system is 
> otherwise occupied).
> 
> I got the following WARNING which was followed by an NMI storm which 
> eventually managed to confuse ext4 enough that my / partition was 
> remounted read-only? Very alarming.
> 
> This is in static void perf_ibs_start(struct perf_event *event, int flags)
> 
> 	if (WARN_ON_ONCE(!(hwc->state & PERF_HES_STOPPED)))
>                 return;

Hurm, its been a long while since I looked at the AMD IBS stuff. But
looking at it I would not be surprised if there's weird interaction
between the HES flags and IBS_flags.

But I'll have to look more careful..

> [  468.763231] Dazed and confused, but trying to continue
> [  468.794184] Uhhuh. NMI received for unknown reason 2d on CPU 2.
> [  468.794184] Do you have a strange power saving mode enabled?
> [  468.794184] Dazed and confused, but trying to continue
> [  473.190535] sd 0:0:0:0: [sda] tag#2 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_TIMEOUT
> [  473.199631] sd 0:0:0:0: [sda] tag#2 CDB: Write(10) 2a 00 39 93 49 d0 00 00 18 00

This might just be the NMI storm starving a device interrupt.