netdev - Re: [PATCH net] dpll: fix build failure due to rcu_dereference

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Message-ID: <0aef1308-89ab-4360-b1d0-f02b82b56bf4@linux.dev>
Date: Thu, 29 Feb 2024 20:42:23 +0000
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net
Cc: netdev@...r.kernel.org, edumazet@...gle.com, pabeni@...hat.com,
 Tasmiya Nalatwad <tasmiya@...ux.vnet.ibm.com>,
 arkadiusz.kubalewski@...el.com, jiri@...nulli.us
Subject: Re: [PATCH net] dpll: fix build failure due to
 rcu_dereference_check() on unknown type

On 29/02/2024 19:05, Jakub Kicinski wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> Tasmiya reports that their compiler complains that we deref
> a pointer to unknown type with rcu_dereference_rtnl():
> 
> include/linux/rcupdate.h:439:9: error: dereferencing pointer to incomplete type ‘struct dpll_pin’
> 
> Unclear what compiler it is, at the moment, and we can't report
> but since DPLL can't be a module - move the code from the header
> into the source file.
> 
> Fixes: 0d60d8df6f49 ("dpll: rely on rcu for netdev_dpll_pin()")
> Reported-by: Tasmiya Nalatwad <tasmiya@...ux.vnet.ibm.com>
> Link: https://lore.kernel.org/all/3fcf3a2c-1c1b-42c1-bacb-78fdcd700389@linux.vnet.ibm.com/
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> ---
> Sending officially the solution Eric suggested in the report
> thread. The bug is pending in the net tree, so I'd like to
> put this on an express path, to make today's PR...
> 
> CC: vadim.fedorenko@...ux.dev
> CC: arkadiusz.kubalewski@...el.com
> CC: jiri@...nulli.us
> ---
>   drivers/dpll/dpll_core.c | 5 +++++
>   include/linux/dpll.h     | 8 ++++----
>   2 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/dpll/dpll_core.c b/drivers/dpll/dpll_core.c
> index 4c2bb27c99fe..507dd9cfb075 100644
> --- a/drivers/dpll/dpll_core.c
> +++ b/drivers/dpll/dpll_core.c
> @@ -42,6 +42,11 @@ struct dpll_pin_registration {
>   	void *priv;
>   };
>   
> +struct dpll_pin *netdev_dpll_pin(const struct net_device *dev)
> +{
> +       return rcu_dereference_rtnl(dev->dpll_pin);
> +}
> +
>   struct dpll_device *dpll_device_get_by_id(int id)
>   {
>   	if (xa_get_mark(&dpll_device_xa, id, DPLL_REGISTERED))
> diff --git a/include/linux/dpll.h b/include/linux/dpll.h
> index 4ec2fe9caf5a..c60591308ae8 100644
> --- a/include/linux/dpll.h
> +++ b/include/linux/dpll.h
> @@ -169,13 +169,13 @@ int dpll_device_change_ntf(struct dpll_device *dpll);
>   
>   int dpll_pin_change_ntf(struct dpll_pin *pin);
>   
> +#if !IS_ENABLED(CONFIG_DPLL)
>   static inline struct dpll_pin *netdev_dpll_pin(const struct net_device *dev)
>   {
> -#if IS_ENABLED(CONFIG_DPLL)
> -	return rcu_dereference_rtnl(dev->dpll_pin);
> -#else
>   	return NULL;
> -#endif
>   }
> +#else
> +struct dpll_pin *netdev_dpll_pin(const struct net_device *dev);
> +#endif
>   
>   #endif

That also works (as well as void *),

Reviewed-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>