From: Rik van Riel <riel@redhat.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Hellwig <hch@infradead.org>,
linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [RFT][PATCH] mm: Fix race in kunmap_atomic()
Date: Wed, 27 Oct 2010 13:46:47 -0400 [thread overview]
Message-ID: <4CC86587.6010506@redhat.com> (raw)
In-Reply-To: <1288191261.15336.1953.camel@twins>
On 10/27/2010 10:54 AM, Peter Zijlstra wrote:
> Christoph reported a nice splat which illustrated a race in the new
> stack based kmap_atomic implementation.
>
> The problem is that we pop our stack slot before we're completely done
> resetting its state -- in particular clearing the PTE (sometimes that's
> CONFIG_DEBUG_HIGHMEM). If an interrupt happens before we actually clear
> the PTE used for the last slot, that interrupt can reuse the slot in a
> dirty state, which triggers a BUG in kmap_atomic().
>
> Fix this by introducing kmap_atomic_idx() which reports the current slot
> index without actually releasing it and use that to find the PTE and
> delay the _pop() until after we're completely done.
>
> Reported-by: Christoph Hellwig<hch@infradead.org>
> Signed-off-by: Peter Zijlstra<a.p.zijlstra@chello.nl>
Acked-by: Rik van Riel <riel@redhat.com>
--
All rights reversed
WARNING: multiple messages have this Message-ID (diff)
From: Rik van Riel <riel@redhat.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Hellwig <hch@infradead.org>,
linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [RFT][PATCH] mm: Fix race in kunmap_atomic()
Date: Wed, 27 Oct 2010 13:46:47 -0400 [thread overview]
Message-ID: <4CC86587.6010506@redhat.com> (raw)
In-Reply-To: <1288191261.15336.1953.camel@twins>
On 10/27/2010 10:54 AM, Peter Zijlstra wrote:
> Christoph reported a nice splat which illustrated a race in the new
> stack based kmap_atomic implementation.
>
> The problem is that we pop our stack slot before we're completely done
> resetting its state -- in particular clearing the PTE (sometimes that's
> CONFIG_DEBUG_HIGHMEM). If an interrupt happens before we actually clear
> the PTE used for the last slot, that interrupt can reuse the slot in a
> dirty state, which triggers a BUG in kmap_atomic().
>
> Fix this by introducing kmap_atomic_idx() which reports the current slot
> index without actually releasing it and use that to find the PTE and
> delay the _pop() until after we're completely done.
>
> Reported-by: Christoph Hellwig<hch@infradead.org>
> Signed-off-by: Peter Zijlstra<a.p.zijlstra@chello.nl>
Acked-by: Rik van Riel <riel@redhat.com>
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All rights reversed
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next prev parent reply other threads:[~2010-10-27 17:47 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-27 12:51 another potentioal kmap rework issue Christoph Hellwig
2010-10-27 14:54 ` [RFT][PATCH] mm: Fix race in kunmap_atomic() Peter Zijlstra
2010-10-27 14:54 ` Peter Zijlstra
2010-10-27 17:46 ` Rik van Riel [this message]
2010-10-27 17:46 ` Rik van Riel
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