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Date: Thu, 18 Sep 2014 10:24:23 -0400 (EDT) From: Alan Stern <stern@...land.harvard.edu> To: Tejun Heo <tj@...nel.org> cc: Petr Mladek <pmladek@...e.cz>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Joe Lawrence <joe.lawrence@...atus.com>, Jiri Kosina <jkosina@...e.cz>, <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2 4/4] usb: hub: rename khubd to hub_wq in documentation and comments 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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