[PATCH 3/4] forcedeth: napi schedule lock fix

[PATCH 3/4] forcedeth: napi schedule lock fix

[Ayaz Abdulla]

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This patch fixes a potential race condition between scheduling napi and 
completing napi poll. The call to netif_rx_schedule should be under 
protection of the lock (as is the completion), otherwise, interrupts 
could be masked off.

Signed-off-by: Ayaz Abdulla <aabdulla@nvidia.com>


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--- old/drivers/net/forcedeth.c	2009-01-09 15:11:55.000000000 -0800
+++ new/drivers/net/forcedeth.c	2009-01-09 15:17:27.000000000 -0800
@@ -3407,10 +3407,10 @@
 
 #ifdef CONFIG_FORCEDETH_NAPI
 		if (events & NVREG_IRQ_RX_ALL) {
+			spin_lock(&np->lock);
 			netif_rx_schedule(dev, &np->napi);
 
 			/* Disable furthur receive irq's */
-			spin_lock(&np->lock);
 			np->irqmask &= ~NVREG_IRQ_RX_ALL;
 
 			if (np->msi_flags & NV_MSI_X_ENABLED)
@@ -3524,10 +3524,10 @@
 
 #ifdef CONFIG_FORCEDETH_NAPI
 		if (events & NVREG_IRQ_RX_ALL) {
+			spin_lock(&np->lock);
 			netif_rx_schedule(dev, &np->napi);
 
 			/* Disable furthur receive irq's */
-			spin_lock(&np->lock);
 			np->irqmask &= ~NVREG_IRQ_RX_ALL;
 
 			if (np->msi_flags & NV_MSI_X_ENABLED)

Re: [PATCH 3/4] forcedeth: napi schedule lock fix

[David Miller]

From: Ayaz Abdulla <aabdulla@nvidia.com>
Date: Fri, 09 Jan 2009 16:03:49 -0500

> This patch fixes a potential race condition between scheduling napi and completing napi poll. The call to netif_rx_schedule should be under protection of the lock (as is the completion), otherwise, interrupts could be masked off.
> 
> Signed-off-by: Ayaz Abdulla <aabdulla@nvidia.com>

Another patch I had to apply by hand.

The 'dev' argument was removed from the netif_*() NAPI interfaces
and then were converted to napi_*() in the net-2.6 tree.

Re: [PATCH 3/4] forcedeth: napi schedule lock fix

[Vitaliy Gusev]

On 10 January 2009 00:03:49 Ayaz Abdulla wrote:
> This patch fixes a potential race condition between scheduling napi and 
> completing napi poll. The call to netif_rx_schedule should be under 
> protection of the lock (as is the completion), otherwise, interrupts 
> could be masked off.

Can you explain how this issue or race can occur (interrupts can be masked off) ?

netif_rx_schedule() merely mark soft irq as waked on current CPU. So dev->poll
will not be called until irq_exit() or local_bh_enable. As nv_nic_irq() is run
under interrupt context, so napi poll will be called only during irq_exit.


> 
> Signed-off-by: Ayaz Abdulla <aabdulla@nvidia.com>
> 
> 



-- 
Thank,
Vitaliy Gusev