Re: [PATCH v14 09/12] unwind deferred: Use SRCU unwind_deferred_task_work()

[Paul E. McKenney]

On Thu, Jul 17, 2025 at 08:25:26AM -0400, Steven Rostedt wrote:
> On Wed, 16 Jul 2025 21:43:47 -0700
> "Paul E. McKenney" <paulmck@xxxxxxxxxx> wrote:
> 
> > > +DEFINE_LOCK_GUARD_1(srcu_lite, struct srcu_struct,  
> > 
> > You need srcu_fast because srcu_lite is being removed.  They are quite
> > similar, but srcu_fast is faster and is NMI-safe.  (This last might or
> > might not matter here.)
> > 
> > See https://lore.kernel.org/all/20250716225418.3014815-3-paulmck@xxxxxxxxxx/
> > for a srcu_fast_notrace, so something like this:
> 
> Yeah, I already saw that patch.
> 
> > 
> > DEFINE_LOCK_GUARD_1(srcu_fast, struct srcu_struct,
> > 		    _T->scp = srcu_read_lock_fast(_T->lock),
> > 		    srcu_read_unlock_fast(_T->lock, _T->scp),
> > 		    struct srcu_ctr __percpu *scp)
> > 
> > Other than that, it looks plausible.
> 
> Using srcu_lite or srcu_fast is an optimization here. And since I saw you
> adding the guard for srcu_fast in that other thread, I'll just use normal
> SRCU here for this series, and in the future we could convert it over to
> srcu_fast.

Works for me!

That said, "in the future" started in -next some time back and is slated
to start in mainline in the upcoming v6.17 merge window.  SRCU-lite is
being removed from the kernel, and has been deprecated via checkpatch.pl.

So if there is some reason that you absolutely cannot immediately convert
to SRCU-fast, let's please discuss.

							Thanx, Paul