linux-kernel - Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all

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Date:	Thu, 01 Apr 2010 18:39:48 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org,
	Kent Overstreet <kent.overstreet@...il.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all_locks()

On 04/01/2010 06:36 PM, Andrea Arcangeli wrote:
> On Thu, Apr 01, 2010 at 01:16:32PM +0200, Peter Zijlstra wrote:
>    
>> On Thu, 2010-04-01 at 14:13 +0300, Avi Kivity wrote:
>>
>>      
>>> If someone is willing to audit all code paths to make sure these locks
>>> are always taken in schedulable context I agree that's a better fix.
>>>        
>> They had better be, they're not irq-safe. Also that's what lockdep is
>> for.
>>      
> In my original patchset I included patches from Christoph to convert
> those locks to mutexes, there was apparently no problem at all with
> that. But frankly I think the only problem here is the warning. The
> only compliant we ever had here is from developers, no users at
> all. If this was a practical problem I think we should have heard
> something by now with so many KVM users out there (and gru too).
>
> The only single reason I'd go for mutexes would be to accommodate
> XPMEM requirements once and for all, no other reason.
>    

There is also a minor benefit for kvm.  Reduced latency over large mmu 
operations; code simplification (we now have some 
copy_from_user_inatomic() that could be simplified).

-- 
error compiling committee.c: too many arguments to function

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