netdev - Re: buggy IFB driver change

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Message-ID: <45BFBE1B.2040508@pobox.com>
Date:	Tue, 30 Jan 2007 16:52:27 -0500
From:	Jeff Garzik <jgarzik@...ox.com>
To:	David Miller <davem@...emloft.net>
CC:	netdev@...r.kernel.org, m.kozlowski@...land.pl,
	Andrew Morton <akpm@...l.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: buggy IFB driver change

David Miller wrote:
> Jeff, please revert: 0c0b3ae68ec93b1db5c637d294647d1cca0df763
> 
> It's wrong.  We had a lengthy analysis of this piece of code
> several months ago, and it is correct.
> 
> Consider, if we run the loop and we get an error
> the following happens:
> 
> 1) attempt of ifb_init_one(i) fails, therefore we should
>    not try to "ifb_free_one()" on "i" since it failed
> 2) the loop iteration first increments "i", then it
>    check for error
> 
> Therefore we must decrement "i" twice before the first
> free during the cleanup.  One to "undo" the for() loop
> increment, and one to "skip" the ifb_init_one() case which
> failed.
> 
> commit 0c0b3ae68ec93b1db5c637d294647d1cca0df763
> Author: Mariusz Kozlowski <m.kozlowski@...land.pl>

Andrew and I both missed that thread, sorry.

I'm about to crash, can you or Linus handle the correction?

	Jeff


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