linux-kernel - Re: [PATCH v2 1/6] hid: new driver for PicoLCD device

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Date:	Mon, 22 Mar 2010 09:54:12 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Bruno Prémont <bonbons@...ux-vserver.org>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Rick L. Vinyard Jr." <rvinyard@...nmsu.edu>,
	Nicu Pavel <npavel@...ner.com>,
	Oliver Neukum <oliver@...kum.org>,
	Jaya Kumar <jayakumar.lkml@...il.com>
Subject: Re: [PATCH v2 1/6] hid: new driver for PicoLCD device

On Sun, 21 Mar 2010, Bruno Prémont wrote:

> > > +	}
> > > +	data->status |= PICOLCD_BUSY;
> > > +	data->pending = work;
> > > +	for (i = k = 0; i < report->maxfield; i++)
> > > +		for (j = 0; j < report->field[i]->report_count; j++) {
> > > +			hid_set_field(report->field[i], j, k < size ? raw_data[k] : 0);
> > > +			k++;
> > > +		}
> > > +	usbhid_submit_report(data->hdev, report, USB_DIR_OUT);
> > > +	complete_all(&data->ready);
> > > +	INIT_COMPLETION(data->ready);
> > 
> > Umm, what does this do, exactly?
> >
> It wakes up anyone waiting on the completion and then resets the completion
> as otherwise any future attempt to wait on it would succeed immediately.
> 
> The complete_all() instead of just complete() comes from the reset() function.
> I can probably reduce it here.
> 
> Will check this combined with your mutex suggestion above.

I am afraid this code is racy as is. You can't be sure that whoever has 
been waiting on the completion has been notified already between 
complete_all() and INIT_COMPLETION(), can you?

Thanks for the driver!

-- 
Jiri Kosina
SUSE Labs, Novell Inc.
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