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 <[EMAIL PROTECTED]>
> ---
>
> 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
-
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