linux-kernel - Re: [RFC 4/9] Atomic reclaim: Save irq flags in vmscan.c

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Message-ID: <20070814203329.GA22202@one.firstfloor.org>
Date:	Tue, 14 Aug 2007 22:33:29 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC 4/9] Atomic reclaim: Save irq flags in vmscan.c

> There are other lock interactions that may cause problems. If we do not 
> switch to the saving of irq flags then all involved spinlocks must become 
> trylocks because the interrupt could have happened while the spinlock is 
> held. So interrupts must be disabled on locks acquired during an 
> interrupt.

I was thinking of a per cpu flag that is set before and unset after
taking the lock in process context. If the flag is set the interrupt
will never try to take the spinlock and return NULL instead. 
That should be equivalent to cli/sti for this special case.

-Andi
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