linux-kernel - Re: Random scheduler/unaligned accesses crashes with perf lock events on sparc 64

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Message-ID: <20100405194055.GA5265@nowhere>
Date:	Mon, 5 Apr 2010 21:40:58 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
	mingo@...e.hu, acme@...hat.com, a.p.zijlstra@...llo.nl,
	paulus@...ba.org
Subject: Re: Random scheduler/unaligned accesses crashes with perf lock
	events on sparc 64

On Mon, Apr 05, 2010 at 12:22:33PM -0700, David Miller wrote:
> From: Frederic Weisbecker <fweisbec@...il.com>
> Date: Mon, 5 Apr 2010 08:57:04 +0200
> 
> > It seems to happen after an unaligned access fixup.
> 
> You shouldn't be getting the unaligned fixup in the first place,
> especially in the locations where you see them.  I suspect that
> once you see first fixup, all of the registers in the cpu have
> been corrupted in one way or another.
> 
> I suspect something fundamental gets corrupted, for example the
> current register window (%cwp) is corrupted and that screws up all of
> the registers so every single function starts accessing garbage.
> 
> My suspicions lie in three places, the ftrace mcount()
> stubs, stack_trace_flush(), or the new perf_arch_save_caller_regs()
> since those are the three places offhand that could make
> us potentially make us return to function in the wrong
> register window.


It happens without CONFIG_FUNCTION_TRACER as well (but it happens
when the function tracer runs). And I hadn't your perf_arch_save_caller_regs()
when I triggered this.

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