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
--- a/drivers/net/macb.c
+++ b/drivers/net/macb.c
@@ -515,14 +515,15 @@
(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 @@
}
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);