linux-kernel - Re: [PATCH v2 4/4] usb: hub: rename khubd to hub

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Message-ID: <20140917212238.GB15795@mtj.dyndns.org>
Date:	Thu, 18 Sep 2014 06:22:38 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Alan Stern <stern@...land.harvard.edu>
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

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.

Thanks.

-- 
tejun
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