linux-kernel - Re: [PATCH] reset: Further simplify locking with guard()

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Message-ID: <9ebdbbdd938ceaa4e58d4cc26e2187fecf5856b8.camel@pengutronix.de>
Date: Mon, 30 Sep 2024 17:26:58 +0200
From: Philipp Zabel <p.zabel@...gutronix.de>
To: Markus Elfring <Markus.Elfring@....de>, kernel@...gutronix.de, 
	linux-arm-kernel@...ts.infradead.org, Krzysztof Kozlowski
	 <krzysztof.kozlowski@...aro.org>
Cc: LKML <linux-kernel@...r.kernel.org>, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] reset: Further simplify locking with guard()

On So, 2024-09-29 at 12:45 +0200, Markus Elfring wrote:
> > Use guard(mutex) to automatically unlock mutexes when going out of
> > scope. Simplify error paths by removing a goto and manual mutex
> > unlocking in multiple places.
> …
> > +++ b/drivers/reset/core.c
> …
> @@ -1041,29 +1036,27 @@ __of_reset_control_get(struct device_node
> *node, const char *id, int index,
>  		}
>  	}
> 
> -	mutex_lock(&reset_list_mutex);
> +	guard(mutex)(&reset_list_mutex);
>  	rcdev = __reset_find_rcdev(&args, gpio_fallback);
> …
>  	rstc = __reset_control_get_internal(rcdev, rstc_id, shared,
> acquired);
> 
> -out_unlock:
> -	mutex_unlock(&reset_list_mutex);
>  out_put:
>  	of_node_put(args.np);
> …
> 
> Would you like to preserve the same lock scope (which ended before
> this function call)?

Thank you for pointing this out. Yes, and this should have alerted me
to the issue with goto out_put from before the locked region.

> @@ -1098,7 +1091,7 @@ __reset_control_get_from_lookup(struct device
> *dev, const char *con_id,
>  	const char *dev_id = dev_name(dev);
>  	struct reset_control *rstc = NULL;
> 
> -	mutex_lock(&reset_lookup_mutex);
> +	guard(mutex)(&reset_lookup_mutex);
> 
>  	list_for_each_entry(lookup, &reset_lookup_list, list) {
> …
>  			break;
>  		}
>  	}
> 
> -	mutex_unlock(&reset_lookup_mutex);
> -
>  	if (!rstc)
>  		return optional ? NULL : ERR_PTR(-ENOENT);
> …
> 
> Would you really like to increase the lock scope here?

I don't think this would have been a problem.

regards
Philipp