Re: [PATCH net] net: usbnet: fix softirq storm on suspend

On Tue, Sep 4, 2012 at 3:49 PM, Bjørn Mork [off-list ref] wrote:

That's easy:

- Take any usbnet device supporting remote wakeup (and of course with a
  minidriver supporting it as well),
- enable autosuspend,
- ip link set dev ethX/usbX/wwanX up

And watch ksoftirqd/X use 100% of one of your CPU cores.

I'd very much like to hear the details if you are unable to reproduce
the bug using this simple test.

I have no such kind of devices, and can't reproduce the problem with
a cdc-ether gadget built by one omap3 beagleboard.

quoted

Once usbnet_terminate_urbs and netif_device_attach() are
completed, who will schedule tasklet to trigger rx_alloc_submit?

That's a good question.  It sure would be nice if that never happened
without waking the device first.  But there are just too many call sites
for me to follow:

To be honest, your patch is correct, and I am just curious about
the reason why tasklet is scheduled after the device is suspended.

bjorn@nemi:/usr/local/src/git/linux$ grep tasklet_schedule drivers/net/usb/usbnet.c
                tasklet_schedule(&dev->bh);
 * but tasklet_schedule() doesn't.  hope the failure is rare.
                        tasklet_schedule (&dev->bh);
        tasklet_schedule(&dev->bh);
                tasklet_schedule(&dev->bh);
        tasklet_schedule (&dev->bh);
                        tasklet_schedule (&dev->bh);
                                tasklet_schedule (&dev->bh);
        tasklet_schedule (&dev->bh);
                                tasklet_schedule (&dev->bh);
                        tasklet_schedule (&dev->bh);

Could you add some debug info inside the caller to see which one
cause the tasklet to be scheduled?


Thanks,
--
Ming Lei
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