linux-kernel - Re: [PATCH] of: Fix locking when calling of_get_next_available

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Message-ID: <5119706F.1080902@gmail.com>
Date:	Mon, 11 Feb 2013 16:27:59 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Grant Likely <grant.likely@...retlab.ca>
CC:	devicetree-discuss@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	Stephen Warren <swarren@...dotorg.org>
Subject: Re: [PATCH] of: Fix locking when calling of_get_next_available_child()

On 02/11/2013 04:19 PM, Grant Likely wrote:
> of_get_next_available_child() obtains the devtree_lock and then calls
> of_device_is_available() which also attempts to claim the lock. This is
> obviously incorrect and causes a deadlock on boot. Fix issue by adding
> an variant of of_device_is_available() which doesn't obtain the lock.
> 
> Cc: Stephen Warren <swarren@...dotorg.org>
> Cc: Rob Herring <robherring2@...il.com>
> Signed-off-by: Grant Likely <grant.likely@...retlab.ca>
> ---
>  drivers/of/base.c |   15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index e8d65af..4af74b7 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -297,7 +297,7 @@ EXPORT_SYMBOL(of_machine_is_compatible);
>   *  Returns 1 if the status property is absent or set to "okay" or "ok",
>   *  0 otherwise
>   */
> -int of_device_is_available(const struct device_node *device)
> +int __of_device_is_available(const struct device_node *device)
>  {
>  	const char *status;
>  	int statlen;
> @@ -313,6 +313,17 @@ int of_device_is_available(const struct device_node *device)
>  
>  	return 0;
>  }
> +
> +int of_device_is_available(const struct device_node *device)

Stephen's version wins because he preserved the documentation. :)

Rob

> +{
> +	unsigned long flags;
> +	int rc;
> +
> +	raw_spin_lock_irqsave(&devtree_lock, flags);
> +	rc = __of_device_is_available(device);
> +	raw_spin_unlock_irqrestore(&devtree_lock, flags);
> +	return rc;
> +}
>  EXPORT_SYMBOL(of_device_is_available);
>  
>  /**
> @@ -404,7 +415,7 @@ struct device_node *of_get_next_available_child(const struct device_node *node,
>  	raw_spin_lock(&devtree_lock);
>  	next = prev ? prev->sibling : node->child;
>  	for (; next; next = next->sibling) {
> -		if (!of_device_is_available(next))
> +		if (!__of_device_is_available(next))
>  			continue;
>  		if (of_node_get(next))
>  			break;
> 

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