linux-kernel - Re: [RFC v1 PATCH 3/6] led: pmic8058: Add PMIC8058 leds driver

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Message-ID: <20101110232840.GA2121@core.coreip.homeip.net>
Date:	Wed, 10 Nov 2010 15:28:41 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Trilok Soni <tsoni@...eaurora.org>, linux-kernel@...r.kernel.org,
	linux-input@...r.kernel.org, rtc-linux@...glegroups.com,
	linux-arm-msm@...r.kernel.org, Richard Purdie <rpurdie@...ys.net>
Subject: Re: [RFC v1 PATCH 3/6] led: pmic8058: Add PMIC8058 leds driver

On Wed, Nov 10, 2010 at 09:45:05PM +0100, Lars-Peter Clausen wrote:
> Trilok Soni wrote:
> > +
> > +static void led_kp_set(struct pmic8058_led_data *led, enum led_brightness value)
> > +{
> > +	int rc;
> > +	u8 level;
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&led->value_lock, flags);
> This function is only ever called from within the workqueue so there is no need for
> locking.
> 

That is a common misconception, unfortunately. The same work may
be executing on several CPUs at the same time if it was scheduled on
multi-threaded work queue.

...

> > +	schedule_work(&led->work);

And sure enough, keventd is such workqueue.

Now, whether having the same work run simultaneously is OK or not is a
different question altogether...

-- 
Dmitry
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