Re: [PATCH 1/3] srcu: Remove superfluous ssp initialization on deferred work queue

[Paul E. McKenney]

On Fri, Apr 02, 2021 at 01:47:02AM +0200, Frederic Weisbecker wrote:
> When an ssp has already started a grace period and queued an early work
> to flush after SRCU workqueues are created, we expect the ssp to be
> properly initialized already. So we can skip this step at this stage.
> 
> Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
> Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
> Cc: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
> Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
> Cc: Uladzislau Rezki <urezki@xxxxxxxxx>
> ---
>  kernel/rcu/srcutree.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index 036ff5499ad5..7197156418e4 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -1396,7 +1396,6 @@ void __init srcu_init(void)
>  	while (!list_empty(&srcu_boot_list)) {
>  		ssp = list_first_entry(&srcu_boot_list, struct srcu_struct,
>  				      work.work.entry);
> -		check_init_srcu_struct(ssp);

You lost me on this one.  What happens if the only pre-initialization
invocation on the statically allocated srcu_struct pointed to by ssp
was call_srcu()?  I am not seeing how the initialization has already
happened in that case.

What am I missing here?

							Thanx, Paul

>  		list_del_init(&ssp->work.work.entry);
>  		queue_work(rcu_gp_wq, &ssp->work.work);
>  	}
> -- 
> 2.25.1
>