netdev - Re: [PATCH] Re: kernel BUG in eth_alloc_tx_desc_index at drivers/net/mv643xx

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Message-ID: <7d01f9f00701230352r6e951b08wea2255ce0baeb40d@mail.gmail.com>
Date:	Tue, 23 Jan 2007 12:52:06 +0100
From:	"Thibaut VARENE" <T-Bone@...isc-linux.org>
To:	"Dale Farnsworth" <dale@...nsworth.org>
Cc:	"Jarek Poplawski" <jarkao2@...pl>, netdev@...r.kernel.org,
	mlachwani@...sta.com
Subject: Re: [PATCH] Re: kernel BUG in eth_alloc_tx_desc_index at drivers/net/mv643xx_eth.c:1069!

On 1/22/07, Dale Farnsworth <dale@...nsworth.org> wrote:
> Jarek and Thibaut,
>
> Thank you both very much for your work finding and fixing this bug.
> Jarek, can you verify that the following patch fixes the problem you
> were seeing?
>
> -Dale

Hi Dale,

The patch seems to work fine. Just thinking out loud (as I really
don't know this part of the kernel), here are a few remarks:

- As Jarek pointed out, you're checking twice the value of
mp->tx_desc_count, which means dereferencing a pointer and accessing
memory twice. I don't know how perf-critical this bit of code is, but
I wonder which of keeping the lock for a long time or doing what you
is better (I'm being anal and you probably know that better than me :)

- Also, lines 344-349, in the test condition, cmd_sts (an indirection
to mp content) is accessed (dunno if it's ok to do that outside of the
lock), and on line 346, mp->stats.tx.errors is incremented outside of
the spinlock protection. But then, I don't know what that lock is
meant to protect, just pointing this out :)

Thanks for your help, I hope the fix will go upstream asap :)

And about being the author of the patch, since I'm not, I don't really mind 8)

HTH

T-Bone

-- 
Thibaut VARENE
http://www.parisc-linux.org/~varenet/
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