Re: [PATCH] hid: usbhid: fix possible deadlock in __usbhid_submit_report

On Sun, 22 Apr 2012, Ming Lei wrote:

On Sun, Apr 22, 2012 at 1:31 AM, Alan Stern [off-list ref] wrote:

quoted

On Sat, 21 Apr 2012, Ming Lei wrote:

quoted

How about always scheduling a tasklet to run what usb_unlink_urb does?
just implement usb_unlink_urb as something like
tasklet_schedule(unlink_tasklet).

Then we can have a uniform lock requirement and no changes are involved
on host controller drivers.

The return values would not be correct.

If you run 'git grep -n usb_unlink_urb drivers/usb/', it may show that
most of callers do not check its return value, and the others only check
for dumping warnings. If usb_unlink_urb is converted into tasklet
implementation, we still can dump these warnings inside its tasklet function.

That sounds rather awkward.  How would the "tasklet-ized" version of 
usb_unlink_urb know what warnings to issue?

quoted

On the other hand, usbnet could call usb_unlink_urb from within a
tasklet.

Sorry, you mean tasklet_schedule can't be called inside a tasklet?

What I meant is: If you're going to run in a tasklet, it doesn't matter
whether the tasklet is started by the usb_unlink_urb function or by its
caller.  The end result should be the same either way.

However Oliver has already objected to using a tasklet for unlinking.

Alan Stern