linux-kernel - Re: [PATCH RFC] x86: avoid atomic operation in test_and_set_bit

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Message-ID: <20110325192601.GC22960@elte.hu>
Date:	Fri, 25 Mar 2011 20:26:01 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jack Steiner <steiner@....com>,
	Jan Beulich <JBeulich@...ell.com>,
	Borislav Petkov <bp@...64.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...nel.dk>,
	"x86@...nel.org" <x86@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>, tee@....com,
	Nikanth Karthikesan <knikanth@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH RFC] x86: avoid atomic operation in test_and_set_bit_lock
 if possible


* Andi Kleen <andi@...stfloor.org> wrote:

> > Could you please try the patch below?
> 
> This is very likely not a good idea.  I heard some systems can hang
> if you overwrite their PMUs this way and you're unlucky enough :-(

Wrong - in that case all kernels from 2.6.32 to 2.6.38 would already be locking 
up. This patch simply restores behavior to essentially what it was before 
v2.6.38 - but also adds the warning.

Thanks,

	Ingo
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