linux-kernel - Re: perf: NULL ptr deref in perf_event_context_sched

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Date:	Wed, 10 Sep 2014 12:02:57 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	paulus@...ba.org, Ingo Molnar <mingo@...nel.org>,
	acme@...stprotocols.net, LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: perf: NULL ptr deref in perf_event_context_sched_in

On Tue, Sep 09, 2014 at 03:23:53PM -0400, Sasha Levin wrote:

> While fuzzing with trinity inside a KVM tools guest running the latest -next
> kernel, I've stumbled on the following spew:
> 
> [ 1181.492212] BUG: unable to handle kernel NULL pointer dereference at 0000000000000040
> [ 1181.500717] IP: perf_event_context_sched_in (kernel/events/core.c:333 kernel/events/core.c:2575)

Oh joy:

static inline struct perf_cpu_context *
__get_cpu_context(struct perf_event_context *ctx)
{
	return this_cpu_ptr(ctx->pmu->pmu_cpu_context);
}

For some reason our pmu::pmu_cpu_context per-cpu storage is gone. Now
how did that happen.... /me puzzled

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