macb: Don't re-enable interrupts while in polling mode

On a busy network, the macb driver could get stuck in the interrupt
handler, quickly triggering the watchdog, due to a confluence of
factors:

 1. macb_poll re-enables interrupts unconditionally, even when it will
    be called again because it exhausted its rx budget

 2. macb_interrupt only disables interrupts after scheduling
    macb_poll, but scheduling fails when macb_poll is already scheduled
    because it didn't call napi_complete

 3. macb_interrupt loops until the interrupt status register is clear,
    which will never happen in this case if the driver doesn't disable
    the RX interrupt

Since macb_interrupt runs in interrupt context, this effectively locks
up the machine, triggering the hardware watchdog.

This issue was readily reproducible on a flooded network with a
modified 2.6.27.48 kernel. The same problem appears to still be in the
2.6.36-rc8 driver code, so I am submitting this patch against that
version. I have not tested this version of the patch except to make
sure the kernel compiles.

Signed-off-by: Joshua Hoke <joshua.hoke@sixnet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/macb.c b/drivers/net/macb.c
index 4297f6e..f69e73e 100644 (file)
--- a/drivers/net/macb.c
+++ b/drivers/net/macb.c
@@ -515,14 +515,15 @@ static int macb_poll(struct napi_struct *napi, int budget)
                (unsigned long)status, budget);
 
        work_done = macb_rx(bp, budget);
-       if (work_done < budget)
+       if (work_done < budget) {
                napi_complete(napi);
 
-       /*
-        * We've done what we can to clean the buffers. Make sure we
-        * get notified when new packets arrive.
-        */
-       macb_writel(bp, IER, MACB_RX_INT_FLAGS);
+               /*
+                * We've done what we can to clean the buffers. Make sure we
+                * get notified when new packets arrive.
+                */
+               macb_writel(bp, IER, MACB_RX_INT_FLAGS);
+       }
 
        /* TODO: Handle errors */
 
@@ -550,12 +551,16 @@ static irqreturn_t macb_interrupt(int irq, void *dev_id)
                }
 
                if (status & MACB_RX_INT_FLAGS) {
+                       /*
+                        * There's no point taking any more interrupts
+                        * until we have processed the buffers. The
+                        * scheduling call may fail if the poll routine
+                        * is already scheduled, so disable interrupts
+                        * now.
+                        */
+                       macb_writel(bp, IDR, MACB_RX_INT_FLAGS);
+
                        if (napi_schedule_prep(&bp->napi)) {
-                               /*
-                                * There's no point taking any more interrupts
-                                * until we have processed the buffers
-                                */
-                               macb_writel(bp, IDR, MACB_RX_INT_FLAGS);
                                dev_dbg(&bp->pdev->dev,
                                        "scheduling RX softirq\n");
                                __napi_schedule(&bp->napi);