linux-kernel - Re: [PATCH rcu 06/11] rcuscale: Provide clear error when async specified without primitives

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Message-ID: <20240814124915.GA1412840@neeraj.linux>
Date: Wed, 14 Aug 2024 18:19:15 +0530
From: Neeraj Upadhyay <Neeraj.Upadhyay@...nel.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: rcu@...r.kernel.org, linux-kernel@...r.kernel.org, kernel-team@...a.com,
	rostedt@...dmis.org, "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH rcu 06/11] rcuscale: Provide clear error when async
 specified without primitives

On Thu, Aug 01, 2024 at 05:43:03PM -0700, Paul E. McKenney wrote:
> Currently, if the rcuscale module's async module parameter is specified
> for RCU implementations that do not have sync primitives such as
> call_rcu(), there will be a series of splats due to calls to a NULL
> pointer.  This commit therefore warns of this situation, but switches
> to non-async testing.
> 

I have changed this to below here [1]. Please let me know if I got it
wrong.

Currently, if the rcuscale module's async module parameter is specified
for RCU implementations that do not have async primitives such as
RCU Tasks Rude, there will be a series of splats due to calls to a NULL
pointer.  This commit therefore warns of this situation, but switches to
non-async testing.


[1] https://git.kernel.org/pub/scm/linux/kernel/git/neeraj.upadhyay/linux-rcu.git/commit/?h=next.14.08.24b&id=22d36840adbcab8fd826a7ca827fd60b708f03de

- Neeraj

> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---
>  kernel/rcu/rcuscale.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
> index 933014b381ec0..315ced63ec105 100644
> --- a/kernel/rcu/rcuscale.c
> +++ b/kernel/rcu/rcuscale.c
> @@ -525,7 +525,7 @@ rcu_scale_writer(void *arg)
>  			schedule_timeout_idle(torture_random(&tr) % writer_holdoff_jiffies + 1);
>  		wdp = &wdpp[i];
>  		*wdp = ktime_get_mono_fast_ns();
> -		if (gp_async) {
> +		if (gp_async && !WARN_ON_ONCE(!cur_ops->async)) {
>  retry:
>  			if (!rhp)
>  				rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
> @@ -597,7 +597,7 @@ rcu_scale_writer(void *arg)
>  			i++;
>  		rcu_scale_wait_shutdown();
>  	} while (!torture_must_stop());
> -	if (gp_async) {
> +	if (gp_async && cur_ops->async) {
>  		cur_ops->gp_barrier();
>  	}
>  	writer_n_durations[me] = i_max + 1;
> -- 
> 2.40.1
>