netdev - Re: [Bugme-new] [Bug 10318] New: WARNING: at arch/x86/mm/highmem_32.c:43 kmap_atomic

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Date:	Tue, 25 Mar 2008 21:23:50 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	netdev@...r.kernel.org, bugme-daemon@...zilla.kernel.org,
	pstaszewski@...com.pl, linux-mm@...ck.org,
	Christoph Lameter <clameter@....com>
Subject: Re: [Bugme-new] [Bug 10318] New: WARNING: at
	arch/x86/mm/highmem_32.c:43 kmap_atomic_prot+0x87/0x184()


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> afacit what's happened is that someone is running __alloc_pages(..., 
> __GFP_ZERO) from softirq context.  But the __GFP_ZERO implementation 
> uses KM_USER0 which cannot be used from softirq context because 
> non-interrupt code on this CPU might be using the same kmap slot.
> 
> Can anyone thing of anything which recently changed in either 
> networking core or e1000e which would have triggered this?
> 
> I think the core MM code is being doubly dumb here.
> 
> a) We should be able to use __GFP_ZERO from all copntexts.
> 
> b) it's not a highmem page anyway, so we won't be using that kmap 
> slot.

i think this came up before (with kzalloc()) and the MM code should have 
been fixed to not even attempt a kmap_atomic(), instead of working it 
around in the callsite or in the kmap_atomic() code.

	Ingo
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