Re: [PATCH] srcu/tiny: Remove preempt_disable/enable() in srcu_gp_start_if_needed()

["Zqiang" <qiang.zhang@linux.dev>]

> 
> On Mon, Sep 08, 2025 at 08:31:55AM +0800, Zqiang wrote:
> 
> > 
> > Currently, the srcu_gp_start_if_needed() is always be invoked in
> >  preempt disable's critical section, this commit therefore remove
> >  redundant preempt_disable/enable() in srcu_gp_start_if_needed().
> >  
> >  Fixes: 65b4a59557f6 ("srcu: Make Tiny SRCU explicitly disable preemption")
> >  Signed-off-by: Zqiang <qiang.zhang@linux.dev>
> > 
> Looks good, but what would be a good way to make this code defend itself
> against being invoked from someplace else that did have preemption
> enabled? Especially given that the Tree SRCU version of this function
> does get invoked with preemption enabled?

ok, maybe we can add lockdep_assert_preemption_disabled() in
the srcu_gp_start_if_needed() ?

Thanks
Zqiang


> 
>  Thanx, Paul
> 
> > 
> > ---
> >  kernel/rcu/srcutiny.c | 3 ---
> >  1 file changed, 3 deletions(-)
> >  
> >  diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> >  index b52ec45698e8..417bd0e4457c 100644
> >  --- a/kernel/rcu/srcutiny.c
> >  +++ b/kernel/rcu/srcutiny.c
> >  @@ -181,10 +181,8 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
> >  {
> >  unsigned long cookie;
> >  
> >  - preempt_disable(); // Needed for PREEMPT_LAZY
> >  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 +192,6 @@ 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
> >
>