Re: [PATCH 01/12] usbnet: introduce usbnet 3 command helpers

On Wed, Oct 10, 2012 at 1:51 PM, Oliver Neukum [off-list ref] wrote:

No, the problem is autoresume.

Suppose we have a device with two interface. Interface A be usbnet; interface B
something you page on. Now consider that you can only resume both interfaces
and this is (and needs to be) done synchronously.

Now we can have this code path:

autoresume of device -> resume() -> kmalloc(..., GFP_KERNEL) ->
VM layer decides to start paging out -> IO to interface B -> autoresume of device
--> DEADLOCK

OK, thanks for your detailed explanation.

We need to use GFP_NOIO in situations the helper cannot know about.
Please add a gfp_t parameter. Then the caller will solve that.

Considered that most of drivers call the helpers in different context, I think
it is better to switch the gpf_t flag runtime inside helpers, like below:

           if (dev->power.runtime_status == RPM_RESUMING)
                   gfp = GFP_NOIO;
          else
                   gfp = GFP_KERNEL;

Thanks,
--
Ming Lei
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html