linux-kernel - Re: perf/ring-buffer: Undefined behaviour in kernel/events/ring

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Message-ID: <20160119143111.GH6344@twins.programming.kicks-ass.net>
Date:	Tue, 19 Jan 2016 15:31:11 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: perf/ring-buffer: Undefined behaviour in
 kernel/events/ring_buffer.c:685:22

On Sun, Jan 10, 2016 at 03:55:13PM -0500, Sasha Levin wrote:
> Hi all,
> 
> While fuzzing with trinity inside a KVM tools guest, running the latest -next
> kernel, I've hit the following warning:
> 
> [ 3494.030114] UBSAN: Undefined behaviour in kernel/events/ring_buffer.c:685:22
> [ 3494.030647] shift exponent -1 is negative

That's rb->page_order == -1, which should 'never' happen, curious!

Funny though that rb::page_order is the exact field _after_ rb::work, ho
humm.