Commit b336369c authored Oct 25, 2010 by Joshua Hoke Committed by David S. Miller Oct 25, 2010

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>

parent c6ce2f4b

drivers/net/macb.c

+16 −11

Original line number	Diff line number	Diff line
		@@ -515,7 +515,7 @@ 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);

		/*
		@@ -523,6 +523,7 @@ static int macb_poll(struct napi_struct *napi, int budget)
		* 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) {
		if (napi_schedule_prep(&bp->napi)) {
		/*
		* There's no point taking any more interrupts
		* until we have processed the buffers
		* 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)) {
		dev_dbg(&bp->pdev->dev,
		"scheduling RX softirq\n");
		__napi_schedule(&bp->napi);

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