On Thu, 18 Sep 2014, Tejun Heo wrote:
> Hello, Alan, Petr.
>
> On Wed, Sep 17, 2014 at 01:36:26PM -0400, Alan Stern wrote:
> > > - /* If khubd ever becomes multithreaded, this will need a lock */
> > > + /* If hub_wq ever becomes multithreaded, this will need a lock */
> > > if (udev->wusb) {
> > > devnum = udev->portnum + 1;
> > > BUG_ON(test_bit(devnum, bus->devmap.devicemap));
> >
> > You probably didn't notice when changing this comment. But in fact,
> > workqueues _are_ multithreaded. Therefore you need to add a lock to
> > this routine.
>
> Haven't read the code but if this function is called from a single
> work_struct, workqueue guarantees that there's only single thread of
> execution at any given time. A work item is never executed
> concurrently no matter what.
This routine can be called from multiple work_structs, because a USB
bus can have multiple hubs.
Alan Stern
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