linux-kernel - Re: SIGSEGV when using "perf record -g" with 3.13-rc* kernel

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Message-ID: <20140110201234.GL7572@laptop.programming.kicks-ass.net>
Date:	Fri, 10 Jan 2014 21:12:34 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Waiman Long <waiman.long@...com>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Aswin Chandramouleeswaran <aswin@...com>,
	Scott J Norton <scott.norton@...com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: SIGSEGV when using "perf record -g" with 3.13-rc* kernel

On Fri, Jan 10, 2014 at 11:56:07AM -0800, Andy Lutomirski wrote:
>  - The perf callchain code tries to read from a bad userspace pointer
> (not sure why -- the ip value in the vsyscall page *is* readable).
> That traps (as expected), but the trap handler injects SIGSEGV due to
> sig_on_uaccess_fault==1.

So the perf thing tries to walk the entire stack in order to obtain a
callchain. Its fairly common to hit crap when attempting this :-)
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