netdev - Re: [PATCH] Fix up truesize after pskb_expand

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Message-Id: <1231144574.3286.15.camel@johannes>
Date:	Mon, 05 Jan 2009 09:36:14 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
	linville@...driver.com, davem <davem@...emloft.net>
Subject: Re: [PATCH] Fix up truesize after pskb_expand_head() in wireless
	stack

On Sun, 2009-01-04 at 19:41 +0100, Andi Kleen wrote:

> I think most adjustments are too small to be noticed. Typically
> they are just for a few bytes in the header. truesize
> is already larger, so it can tolerate some slag.

This statement is incompatible with your patch when you think about the
exact definition of truesize and the (unconditional!) adjustments your
patch makes.

> I also only see it occasionally (maybe 5-10 times/day) when
> the wireless stack appends a lot of data.

Except the data it appends should generally be of the same or very
similar size under unchanging conditions, so that doesn't make a lot of
sense either.

> My proposal would be to include this patch for 2.6.28/2.6.29
> and investigate fixing pskb_expand_head for 2.6.30.

I disagree, obviously. I knew there was some truesize corruption, and I
think you for tracing down where it occurs. I'll investigate a proper
fix when I get around to that, meanwhile I don't think the problem is
awfully urgent since we've had this going on for quite a while and, if
any, it probably only affects/corrupts the raw monitor sockets.

johannes

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