netdev - Re: [Kgdb-bugreport] [PATCH] 8139too: harden against TX ring overflow

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Date:	Fri, 25 May 2007 01:44:30 +0400
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	netdev@...r.kernel.org, mhuth@...sta.com,
	kgdb-bugreport@...ts.sourceforge.net
Subject: Re: [Kgdb-bugreport] [PATCH] 8139too: harden against TX ring overflow

Jeff Garzik wrote:

>>> This driver's 4-packet deep TX queue is too sensible to the 
>>> "careless" callers
>>> ignoring its state (like netpoll in trapped mode), so add "queue 
>>> full" check at
>>> the start of the hard_start_xmit() method (only under #ifndef 
>>> RTL8139_NDEBUG,
>>> otherwise the queue will get stuck once dirty pointer gets out of 
>>> sync); switch
>>> to using appropriate mnemonics for the return values while at it.
>>> Also, the out-of-sync dirty pointer check is misplaced in 
>>> rtl8139_tx_interrupt()
>>> which causes TX descriptors to be inspected more than once in case 
>>> the pointer
>>> really gets out-of-sync (and incrementing the dirty pointer always by 
>>> 4 is just
>>> not enough, e.g. KGDBoE managed to stuff 20+ extra buffers into the 
>>> queue) --
>>> place it before the loop and limit the loop to only look through 4 
>>> descriptors
>>> at most, so that already overwritten descriptors are just not counted.

>>> Signed-off-by: Sergei Shtylyov <sshtylyov@...mvista.com>

>>    Jeff, do you have any opinion on this patch?

> The out-of-sync dirty pointer check is leftover boilerplate, and not 
> really indicative of anything except for some code to be removed.

> As for the other stuff, I would say "fix the caller".  We don't need to 
> hack every driver for cases where netpoll is being dumb.

    Caller's been fixed now. So, I read that as reject. :-)

>     Jeff

WBR, Sergei
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