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

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Message-ID: <dfcc1432-6230-42ae-b3d4-0081918bc979@paulmck-laptop>
Date: Wed, 14 Aug 2024 08:09:04 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Neeraj Upadhyay <Neeraj.Upadhyay@...nel.org>
Cc: rcu@...r.kernel.org, linux-kernel@...r.kernel.org, kernel-team@...a.com,
	rostedt@...dmis.org
Subject: Re: [PATCH rcu 06/11] rcuscale: Provide clear error when async
 specified without primitives

On Wed, Aug 14, 2024 at 06:19:15PM +0530, Neeraj Upadhyay wrote:
> 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.

How about something like this, but perhaps wordsmithed a bit?

	"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 (which now lacks
	a call_rcu_tasks_rude() function), 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."

							Thanx, Paul

> [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
> >