linux-kernel - Re: [RESEND PATCH V2] leds: sc27xx: Move mutex

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Date:   Fri, 13 Oct 2023 11:19:59 +0100
From:   Lee Jones <lee@...nel.org>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     Chunyan Zhang <chunyan.zhang@...soc.com>,
        Pavel Machek <pavel@....cz>, linux-leds@...r.kernel.org,
        Orson Zhai <orsonzhai@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH V2] leds: sc27xx: Move mutex_init() to the end of
 probe

On Thu, 12 Oct 2023, Baolin Wang wrote:

> 
> 
> On 10/12/2023 5:16 PM, Lee Jones wrote:
> > On Thu, 12 Oct 2023, Baolin Wang wrote:
> > 
> > > 
> > > 
> > > On 10/12/2023 11:47 AM, Chunyan Zhang wrote:
> > > > Move the mutex_init() to avoid redundant mutex_destroy() calls after
> > > > that for each time the probe fails.
> > > > 
> > > > Signed-off-by: Chunyan Zhang <chunyan.zhang@...soc.com>
> > > > ---
> > > > Rebased onto linux-next.
> > > > 
> > > > V2:
> > > > - Move the mutex_init() to the end of .probe() instead of adding
> > > > mutex_destroy() according to Lee's comments.
> > > > ---
> > > >    drivers/leds/leds-sc27xx-bltc.c | 9 ++++-----
> > > >    1 file changed, 4 insertions(+), 5 deletions(-)
> > > > 
> > > > diff --git a/drivers/leds/leds-sc27xx-bltc.c b/drivers/leds/leds-sc27xx-bltc.c
> > > > index af1f00a2f328..ef57e57ecf07 100644
> > > > --- a/drivers/leds/leds-sc27xx-bltc.c
> > > > +++ b/drivers/leds/leds-sc27xx-bltc.c
> > > > @@ -296,7 +296,6 @@ static int sc27xx_led_probe(struct platform_device *pdev)
> > > >    		return -ENOMEM;
> > > >    	platform_set_drvdata(pdev, priv);
> > > > -	mutex_init(&priv->lock);
> > > >    	priv->base = base;
> > > >    	priv->regmap = dev_get_regmap(dev->parent, NULL);
> > > >    	if (!priv->regmap) {
> > > > @@ -309,13 +308,11 @@ static int sc27xx_led_probe(struct platform_device *pdev)
> > > >    		err = of_property_read_u32(child, "reg", &reg);
> > > >    		if (err) {
> > > >    			of_node_put(child);
> > > > -			mutex_destroy(&priv->lock);
> > > >    			return err;
> > > >    		}
> > > >    		if (reg >= SC27XX_LEDS_MAX || priv->leds[reg].active) {
> > > >    			of_node_put(child);
> > > > -			mutex_destroy(&priv->lock);
> > > >    			return -EINVAL;
> > > >    		}
> > > > @@ -325,9 +322,11 @@ static int sc27xx_led_probe(struct platform_device *pdev)
> > > >    	err = sc27xx_led_register(dev, priv);
> > > >    	if (err)
> > > > -		mutex_destroy(&priv->lock);
> > > > +		return err;
> > > > -	return err;
> > > > +	mutex_init(&priv->lock);
> > > 
> > > I think it is better to prepare all the required resources before
> > > registering the led device, what I mean is moving mutex_init() before
> > > calling sc27xx_led_register().
> > 
> > Is the mutex used before this point?
> > 
> > If not, I don't see any reason to initialise it sooner.
> 
> When inserting the led module, after registering the led device, users can
> set the led brightness or pattern trigger before initializing the mutex,
> which will crash the system. I know this may not be an actual scenario, but
> this patch opens a small race window, that's what I concerned.

If there's a good technical reason to move it, then we should.

-- 
Lee Jones [李琼斯]