linux-kernel - Re: [PATCH v2] srcu/tiny: Remove preempt_disable/enable() in srcu_gp_start_if

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Message-ID: <e5e69dc3-ebd3-47ae-b193-bc4b2de36904@paulmck-laptop>
Date: Wed, 10 Sep 2025 08:52:20 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Joel Fernandes <joelagnelf@...dia.com>
Cc: Zqiang <qiang.zhang@...ux.dev>, frederic@...nel.org,
	neeraj.upadhyay@...nel.org, boqun.feng@...il.com, urezki@...il.com,
	rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] srcu/tiny: Remove preempt_disable/enable() in
 srcu_gp_start_if_needed()

On Wed, Sep 10, 2025 at 10:36:20AM -0400, Joel Fernandes wrote:
> [..]
> > >  kernel/rcu/srcutiny.c | 4 +---
> > >  1 file changed, 1 insertion(+), 3 deletions(-)
> > > 
> > > diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> > > index b52ec45698e8..b2da188133fc 100644
> > > --- a/kernel/rcu/srcutiny.c
> > > +++ b/kernel/rcu/srcutiny.c
> > > @@ -181,10 +181,9 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
> > >  {
> > >  	unsigned long cookie;
> > >  
> > > -	preempt_disable();  // Needed for PREEMPT_LAZY
> > > +	lockdep_assert_preemption_disabled();
> 
> nit: Do we still want to keep the comment that the expectation of preemption
> being disabled is for the LAZY case?

Good point, and I do believe that we do.  Zqiang, any reason not to
add this comment back in?

							Thanx, Paul

> thanks,
> 
>  - Joel
> 
> 
> > >  	cookie = get_state_synchronize_srcu(ssp);
> > >  	if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) {
> > > -		preempt_enable();
> > >  		return;
> > >  	}
> > >  	WRITE_ONCE(ssp->srcu_idx_max, cookie);
> > > @@ -194,7 +193,6 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
> > >  		else if (list_empty(&ssp->srcu_work.entry))
> > >  			list_add(&ssp->srcu_work.entry, &srcu_boot_list);
> > >  	}
> > > -	preempt_enable();
> > >  }
> > >  
> > >  /*
> > > -- 
> > > 2.48.1
> > >