Re: perf_fuzzer crash on pentium 4

From: Vince Weaver <vincent.weaver@maine.edu>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Vince Weaver <vincent.weaver@maine.edu>,
	linux-kernel@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: perf_fuzzer crash on pentium 4
Date: Tue, 6 May 2014 17:30:19 -0400 (EDT)	[thread overview]
Message-ID: <alpine.DEB.2.10.1405061729350.4849@vincent-weaver-1.umelst.maine.edu> (raw)
In-Reply-To: <20140506202307.GA1458@moon>

On Wed, 7 May 2014, Cyrill Gorcunov wrote:

> > [   67.872274] BUG: unable to handle kernel NULL pointer dereference at 00000004
> > [   67.876146] IP: [<ffffffff81013df2>] p4_pmu_schedule_events+0xa5/0x331
> 
> This looks like
> 
> p4_pmu_schedule_events:
> 		...
> 		bind = p4_config_get_bind(hwc->config);
> 			returned bind = NULL;
> 		escr_idx = p4_get_escr_idx(bind->escr_msr[thread]); NULL deref
> 
> If i'm right (btw it's possible to use addr2line helper?) 

Yes, the address maps to

	escr_idx = p4_get_escr_idx(bind->escr_msr[thread]);

> then hwc->config
> is corrupted and p4_config_get_bind returned nil simply because proper event
> was not found. And I don't understand how it could happen because before
> configuration gets written into hwc->config it's validated once obtained
> from user-space as a raw event. Weird...

I'll try to get some sort of trace out if it to see what event is being 
tried.

Vince