linux-kernel - Re: 2.6.24-git: kmap_atomic() WARN

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Message-ID: <47C43F18.6060207@pobox.com>
Date:	Tue, 26 Feb 2008 11:32:24 -0500
From:	Jeff Garzik <jgarzik@...ox.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Björn Steinbrink <B.Steinbrink@....de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.24-git: kmap_atomic() WARN_ON()

Ingo Molnar wrote:
> * Jeff Garzik <jgarzik@...ox.com> wrote:
> 
>> +	unsigned long flags;
>> +
>> +	local_irq_save(flags);
> 
> hm, couldnt we attach the irq disabling to some spinlock, in a natural 
> way? Explicit flags fiddling is a PITA once we do things like threaded 
> irq handlers, -rt, etc.

Attaching the irq disabling to some spinlock is what would be 
artificial...  See the ahci.c patch earlier in this thread.  It is taken 
without spin_lock_irqsave() in the interrupt handler, and there is no 
reason to disable interrupts for the entirety of the interrupt handler 
run -- only the part where we call kmap.

This is only being done to satisfy kmap_atomic's requirements, not libata's.

I could add a "kmap lock" but that just seems silly.

	Jeff

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