netdev - Re: [PATCH] b44: netpoll locking fix

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Message-ID: <20070529222041.GB31200@electric-eye.fr.zoreil.com>
Date:	Wed, 30 May 2007 00:20:41 +0200
From:	Francois Romieu <romieu@...zoreil.com>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
Cc:	Gary Zambrano <zambrano@...adcom.com>, jgarzik@...ox.com,
	akpm@...ux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH] b44: netpoll locking fix

Stephen Hemminger <shemminger@...ux-foundation.org> :
⅜...]
> Better to just get rid of using the lock as a transmit lock and
> use netif_tx_lock instead.
> --- a/drivers/net/b44.c	2007-05-29 09:51:43.000000000 -0700
> +++ b/drivers/net/b44.c	2007-05-29 14:26:03.000000000 -0700
> @@ -607,6 +607,7 @@ static void b44_tx(struct b44 *bp)
>  {
>  	u32 cur, cons;
>  
> +	netif_tx_lock(bp->dev);
>  	cur  = br32(bp, B44_DMATX_STAT) & DMATX_STAT_CDMASK;
>  	cur /= sizeof(struct dma_desc);
>  

(damn, you are quick)

I am not completely convinced.

1. netpoll_send_skb (calls netif_tx_trylock(dev))
   -> netpoll_poll(np)
      -> poll_napi(np)
         -> np->dev->poll(np->dev, &budget) ( == b44_poll)
            -> b44_tx
               -> netif_tx_lock(bp->dev) *deadlock*

2. Hunk #5 clashes with John Linville's wireless-dev#master

3. Moderately appropriate for 2.6.22-rc (imho, fwiw, etc.)

-- 
Ueimor
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