linux-kernel - Re: [perf] yet another 32/64-bit range check failure

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Message-ID: <alpine.DEB.2.10.1404230930090.29827@vincent-weaver-1.um.maine.edu>
Date:	Wed, 23 Apr 2014 09:33:56 -0400 (EDT)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [perf] yet another 32/64-bit range check failure

On Wed, 23 Apr 2014, Peter Zijlstra wrote:
> 
> So perf_event_open() -> err_alloc: -> free_event() -> __free_event() ->
> call_rcu() -> free_event_rcu() -> kfree().
> 
> Would explain that, right? The memory is RCU freed, which means we need
> to wait a grace period before releasing it.

ah yes, RCU.  That does make debugging this issue a lot harder.

Back to trying to get the bug to trigger in a useful location while ftrace 
is running.  I keep triggering it immediately after the compiler generates 
helpful code like
	mov    0x40(%rbx),%rbx
so the address is lost and the register dump just holds 0x6b6b6b6b6b6b6b6b.

Vince

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