netdev - Re: kmap_atomic() oopses in current mainline

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Message-ID: <20070719092856.GA15839@2ka.mipt.ru>
Date:	Thu, 19 Jul 2007 13:28:56 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	netdev@...r.kernel.org, linux-kernel-announce@...r.kernel.org,
	Dan Williams <dan.j.williams@...el.com>
Subject: Re: kmap_atomic() oopses in current mainline

Hi.

On Thu, Jul 19, 2007 at 01:33:04AM -0700, Andrew Morton (akpm@...ux-foundation.org) wrote:
> I don't think the 2-year-old Vaio has offload engine support ;) Dan, this:
> 
> +		if (flags & ASYNC_TX_KMAP_DST)
> +			dest_buf = kmap_atomic(dest, KM_USER0) + dest_offset;
> +		else
> +			dest_buf = page_address(dest) + dest_offset;
> +
> +		if (flags & ASYNC_TX_KMAP_SRC)
> +			src_buf = kmap_atomic(src, KM_USER0) + src_offset;
> +		else
> +			src_buf = page_address(src) + src_offset;
> +
> +		memcpy(dest_buf, src_buf, len);
> +
> +		if (flags & ASYNC_TX_KMAP_DST)
> +			kunmap_atomic(dest_buf, KM_USER0);
> +
> +		if (flags & ASYNC_TX_KMAP_SRC)
> +			kunmap_atomic(src_buf, KM_USER0);
> +
> 
> is very wrong if both ASYNC_TX_KMAP_DST and ASYNC_TX_KMAP_SRC can ever be
> set.  We'll end up using the same kmap slot for both src add dest and we
> get either corrupted data or a BUG.

So far it can not since the only user is raid code, which only allows to
perform either reading from bio or writing into one, which requires only
one mapping.

Btw, shouldn't it always be kmap_atomic() even if flag is not set.
That pages are usual one returned by alloc_page().
 

-- 
	Evgeniy Polyakov
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