linux-kernel - Re: [PATCH 2/2] srcu: Early test SRCU polling start

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Date:   Wed, 14 Apr 2021 08:56:36 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Josh Triplett <josh@...htriplett.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 2/2] srcu: Early test SRCU polling start

On Wed, Apr 14, 2021 at 03:24:13PM +0200, Frederic Weisbecker wrote:
> Test an early call to start_poll_synchronize_srcu() and place it before
> the early test to call_srcu() on the same ssp.
> 
> After the later call to srcu_barrier(), we expect the first grace period
> completion to be visible by a subsequent call to
> poll_state_synchronize_srcu(). Report otherwise.
> 
> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>

Given the first patch, this one looks good, give or take my usual
editing compulsion.

							Thanx, Paul

> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Lai Jiangshan <jiangshanlai@...il.com>
> Cc: Neeraj Upadhyay <neeraju@...eaurora.org>
> Cc: Josh Triplett <josh@...htriplett.org>
> Cc: Joel Fernandes <joel@...lfernandes.org>
> Cc: Uladzislau Rezki <urezki@...il.com>
> ---
>  kernel/rcu/update.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> index dd94a602a6d2..c21b38cc25e9 100644
> --- a/kernel/rcu/update.c
> +++ b/kernel/rcu/update.c
> @@ -524,6 +524,7 @@ static void test_callback(struct rcu_head *r)
>  }
>  
>  DEFINE_STATIC_SRCU(early_srcu);
> +static unsigned long early_srcu_cookie;
>  
>  struct early_boot_kfree_rcu {
>  	struct rcu_head rh;
> @@ -536,8 +537,10 @@ static void early_boot_test_call_rcu(void)
>  	struct early_boot_kfree_rcu *rhp;
>  
>  	call_rcu(&head, test_callback);
> -	if (IS_ENABLED(CONFIG_SRCU))
> +	if (IS_ENABLED(CONFIG_SRCU)) {
> +		early_srcu_cookie = start_poll_synchronize_srcu(&early_srcu);
>  		call_srcu(&early_srcu, &shead, test_callback);
> +	}
>  	rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
>  	if (!WARN_ON_ONCE(!rhp))
>  		kfree_rcu(rhp, rh);
> @@ -563,6 +566,7 @@ static int rcu_verify_early_boot_tests(void)
>  		if (IS_ENABLED(CONFIG_SRCU)) {
>  			early_boot_test_counter++;
>  			srcu_barrier(&early_srcu);
> +			WARN_ON_ONCE(!poll_state_synchronize_srcu(&early_srcu, early_srcu_cookie));
>  		}
>  	}
>  	if (rcu_self_test_counter != early_boot_test_counter) {
> -- 
> 2.25.1
>