From: "Dale Farnsworth" <dale@farnsworth.org>
To: "Steven J. Hill" <sjhill@realitydiluted.com>
Cc: netdev@vger.kernel.org
Subject: Re: [PATCH] Merge GT/MV642xx Support into MV643xx Driver [8/8]
Date: Thu, 19 Jul 2007 07:45:02 -0700 [thread overview]
Message-ID: <20070719144502.GG12892@xyzzy.farnsworth.org> (raw)
In-Reply-To: <469EF04C.1020505@realitydiluted.com>
On Thu, Jul 19, 2007 at 05:02:04AM +0000, Steven J. Hill wrote:
> Fix long standing panic with regards to descriptors and locking.
>
> Signed-off-by: Steven J. Hill <sjhill1@rockwellcollins.com>
> ---
>
> diff -ur linux-2.6.22.1/drivers/net/mv643xx_eth.c linux-2.6.22.1-rci/drivers/net/mv643xx_eth.c
> --- linux-2.6.22.1/drivers/net/mv643xx_eth.c 2007-07-18 22:55:11.000000000 -0500
> +++ linux-2.6.22.1-rci/drivers/net/mv643xx_eth.c 2007-07-18 22:39:37.000000000 -0500
> @@ -350,13 +350,6 @@
>
> while (mp->tx_desc_count > 0) {
> spin_lock_irqsave(&mp->lock, flags);
> -
> - /* tx_desc_count might have changed before acquiring the lock */
> - if (mp->tx_desc_count <= 0) {
> - spin_unlock_irqrestore(&mp->lock, flags);
> - return released;
> - }
> -
The code you remove above is needed to protect against a nasty bug.
It was added in January and needs to stay in.
> @@ -367,7 +360,7 @@
>
> if (!force && (cmd_sts & ETH_BUFFER_OWNED_BY_DMA)) {
> spin_unlock_irqrestore(&mp->lock, flags);
> - return released;
> + continue;
> }
No. Continuing at that point results in the driver spinning, wasting
cpu while polling for the hardware to release the DMA descriptor.
> @@ -1488,7 +1481,19 @@
> BUG_ON(netif_queue_stopped(dev));
> BUG_ON(skb == NULL);
>
> - if (mp->tx_ring_size - mp->tx_desc_count < MAX_DESCS_PER_SKB) {
> + if (mp->tx_ring_size - mp->tx_desc_count <= MAX_DESCS_PER_SKB) {
> + /*
> + * We are completely out of TX descriptors, however,
> + * if 'tx_used_desc_q' is zero, most likely the port
> + * has been configured and is up, but there is no link.
> + * We attempt to free a single descriptor to keep the
> + * 'sendto' call and rest of the stack happy. If this
> + * check is taken out, expect an error and kernel panic
> + * from 'kernel/softirq.c:141' inside 'local_bh_enable'.
> + */
> + if (mp->tx_used_desc_q == 0)
> + mv643xx_eth_free_all_tx_descs(dev);
I don't understand the bug, but regardless, we need a better fix.
Freeing all the descriptors when the HW xmit queue is full is not
a solution.
-Dale
prev parent reply other threads:[~2007-07-19 14:45 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-07-19 5:02 [PATCH] Merge GT/MV642xx Support into MV643xx Driver [8/8] Steven J. Hill
2007-07-19 14:45 ` Dale Farnsworth [this message]
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