[Linux-kernel-mentees] [PATCH] kernel: audit.c: Add __rcu notation to RCU pointer

[Joel Fernandes]

On Tue, Nov 26, 2019 at 10:57:23PM +0530, Amol Grover wrote:
> add __rcu notation to RCU protected global pointer auditd_conn
> 
> Fixes multiple instances of sparse error:
> error: incompatible types in comparison expression
> (different address spaces)
> 
> Signed-off-by: Amol Grover <frextrite at gmail.com>
> ---
>  kernel/audit.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/audit.c b/kernel/audit.c
> index da8dc0db5bd3..30e7fc9b8da2 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -102,12 +102,14 @@ struct audit_net {
>   * This struct is RCU protected; you must either hold the RCU lock for reading
>   * or the associated spinlock for writing.
>   */
> -static struct auditd_connection {
> +struct auditd_connection {
>  	struct pid *pid;
>  	u32 portid;
>  	struct net *net;
>  	struct rcu_head rcu;
> -} *auditd_conn = NULL;
> +};
> +static struct auditd_connection __rcu *auditd_conn;
> +RCU_INIT_POINTER(auditd_conn);

Looks like this causes a build error. Always please build test your patches
in the very least. And I also did not understand how RCU_INIT_POINTER can
even be used outside of a function. In C, executable code cannot be outside
functions.

Is doing the following not sufficient to fix the sparse issue?

thanks,

 - Joel

---8<-----------------------

diff --git a/kernel/audit.c b/kernel/audit.c
index 49b6049b26ac..c5d4b5a2dea1 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -108,8 +108,8 @@ struct auditd_connection {
 	struct net *net;
 	struct rcu_head rcu;
 };
-static struct auditd_connection __rcu *auditd_conn;
-RCU_INIT_POINTER(auditd_conn);
+static struct auditd_connection __rcu *auditd_conn = NULL;
+
 static DEFINE_SPINLOCK(auditd_conn_lock);
 
 /* If audit_rate_limit is non-zero, limit the rate of sending audit records