Re: [PATCH] firmware: Hold a reference for of_find_compatible_node()

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Jun 21, 2022 at 11:26:25AM +0800, Liang He wrote:
> In of_register_trusted_foundations(), we need to hold the reference
> returned by of_find_compatible_node() and then use it to call
> of_node_put() for refcount balance.
> 
> Signed-off-by: Liang He <windhl@126.com>
> ---
>  include/linux/firmware/trusted_foundations.h | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/firmware/trusted_foundations.h b/include/linux/firmware/trusted_foundations.h
> index be5984bda592..399471c2f1c7 100644
> --- a/include/linux/firmware/trusted_foundations.h
> +++ b/include/linux/firmware/trusted_foundations.h
> @@ -71,12 +71,16 @@ static inline void register_trusted_foundations(
>  
>  static inline void of_register_trusted_foundations(void)
>  {
> +	struct device_node *np = of_find_compatible_node(NULL, NULL, "tlm,trusted-foundations");
> +
> +	of_node_put(np);
> +	if (!np)

While this is technically correct, you are now checking to see if this
points to a memory location that you no longer know what it really
belongs to.  C will let you do this, but it might be nicer to fix it up
properly so it doesn't look like this.

thanks,

greg k-h