Re: [PATCH v2 2/9] rcu: Mark rcu_dynticks_curr_cpu_in_eqs() inline

Joel Fernandes
2020-02-12T22:38:20Z

On Wed, Feb 12, 2020 at 10:01:41PM +0100, Peter Zijlstra wrote:
> Since rcu_is_watching() is notrace (and needs to be, as it can be
> called from the tracers), make sure everything it in turn calls is
> notrace too.
>
> To that effect, mark rcu_dynticks_curr_cpu_in_eqs() inline, which
> implies notrace, as the function is tiny.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> kernel/rcu/tree.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -294,7 +294,7 @@ static void rcu_dynticks_eqs_online(void
> *
> * No ordering, as we are sampling CPU-local information.
> */
> -static bool rcu_dynticks_curr_cpu_in_eqs(void)
> +static inline bool rcu_dynticks_curr_cpu_in_eqs(void)

I think there are ways to turn off function inlining, such as gcc's:
-fkeep-inline-functions

And just to be sure weird compilers (clang *cough*) don't screw this up,
could we make it static inline notrace?

Build tested it on the tip tree on top of your patch:

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

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f3cb824fe5bbf..078d56951c8e7 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -294,7 +294,7 @@ static void rcu_dynticks_eqs_online(void)
*
* No ordering, as we are sampling CPU-local information.
*/
-static inline bool rcu_dynticks_curr_cpu_in_eqs(void)
+static inline notrace bool rcu_dynticks_curr_cpu_in_eqs(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);