Re: [PATCH 03/24] rcu/tree: Use consistent style for comments

Joel Fernandes
2020-05-04T00:39:16Z

On Sun, May 03, 2020 at 05:26:56PM -0700, Paul E. McKenney wrote:
> On Sun, May 03, 2020 at 07:52:13PM -0400, Joel Fernandes wrote:
> > On Fri, May 01, 2020 at 12:05:55PM -0700, Paul E. McKenney wrote:
> > > On Tue, Apr 28, 2020 at 10:58:42PM +0200, Uladzislau Rezki (Sony) wrote:
> > > > From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
> > > >
> > > > Simple clean up of comments in kfree_rcu() code to keep it consistent
> > > > with majority of commenting styles.
> > > >
> > > > Reviewed-by: Uladzislau Rezki <urezki@gmail.com>
> > > > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> > >
> > > Hmmm...
> > >
> > > Exactly why is three additional characters per line preferable? Or in
> > > the case of block comments, either one or two additional lines, depending
> > > on /* */ style?
> >
> > I prefer to keep the code consistent and then bulk convert it later. Its a
> > bit ugly to read when its mixed up with "//" and "/* */" right now. We can
> > convert it to // all at once later but until then it'll be good to keep it
> > consistent in this file IMO. When I checked the kfree_rcu() code, it had more
> > "/* */" than not, so this small change is less churn for now.
>
> Please just drop this patch along with the other "//"-to-"/* */"
> regressions.

Right now in your rcu/dev branch (without applying this series),in
kfree_rcu_drain_unlock() and the functions before and after it, it is
inconsistent.

Also in kfree_call_rcu(), it is:

// Queue the object but don't yet schedule the batch.
if (debug_rcu_head_queue(head)) {
// Probable double kfree_rcu(), just leak.
WARN_ONCE(1, "%s(): Double-freed call. rcu_head %p\n",
__func__, head);
goto unlock_return;
}

/*
* Under high memory pressure GFP_NOWAIT can fail,
* in that case the emergency path is maintained.
*/

> If you want to convert more comments to "//" within the confines of the
> kfree_rcu() code, I am probably OK with that. But again, a big-bang
> change of this sort often causes problems due to lots of potential
> rebase/merge conflicts.

Ok. Since this series touched kfree-related RCU code, converting all of the
kfree-related RCU code to "//" is Ok with me. Just wanted to keep it
consistent :)

thanks,

- Joel

>
> Thanx, Paul
>
> > thanks,
> >
> > - Joel
> >
> > >
> > > I am (slowly) moving RCU to "//" for those reasons. ;-)
> > >
> > > Thanx, Paul
> > >
> > > > ---
> > > > kernel/rcu/tree.c | 16 ++++++++--------
> > > > 1 file changed, 8 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > > index cd61649e1b00..1487af8e11e8 100644
> > > > --- a/kernel/rcu/tree.c
> > > > +++ b/kernel/rcu/tree.c
> > > > @@ -3043,15 +3043,15 @@ static inline bool queue_kfree_rcu_work(struct kfree_rcu_cpu *krcp)
> > > > static inline void kfree_rcu_drain_unlock(struct kfree_rcu_cpu *krcp,
> > > > unsigned long flags)
> > > > {
> > > > - // Attempt to start a new batch.
> > > > + /* Attempt to start a new batch. */
> > > > krcp->monitor_todo = false;
> > > > if (queue_kfree_rcu_work(krcp)) {
> > > > - // Success! Our job is done here.
> > > > + /* Success! Our job is done here. */
> > > > raw_spin_unlock_irqrestore(&krcp->lock, flags);
> > > > return;
> > > > }
> > > >
> > > > - // Previous RCU batch still in progress, try again later.
> > > > + /* Previous RCU batch still in progress, try again later. */
> > > > krcp->monitor_todo = true;
> > > > schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
> > > > raw_spin_unlock_irqrestore(&krcp->lock, flags);
> > > > @@ -3151,14 +3151,14 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> > > > unsigned long flags;
> > > > struct kfree_rcu_cpu *krcp;
> > > >
> > > > - local_irq_save(flags); // For safely calling this_cpu_ptr().
> > > > + local_irq_save(flags); /* For safely calling this_cpu_ptr(). */
> > > > krcp = this_cpu_ptr(&krc);
> > > > if (krcp->initialized)
> > > > raw_spin_lock(&krcp->lock);
> > > >
> > > > - // Queue the object but don't yet schedule the batch.
> > > > + /* Queue the object but don't yet schedule the batch. */
> > > > if (debug_rcu_head_queue(head)) {
> > > > - // Probable double kfree_rcu(), just leak.
> > > > + /* Probable double kfree_rcu(), just leak. */
> > > > WARN_ONCE(1, "%s(): Double-freed call. rcu_head %p\n",
> > > > __func__, head);
> > > > goto unlock_return;
> > > > @@ -3176,7 +3176,7 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> > > >
> > > > WRITE_ONCE(krcp->count, krcp->count + 1);
> > > >
> > > > - // Set timer to drain after KFREE_DRAIN_JIFFIES.
> > > > + /* Set timer to drain after KFREE_DRAIN_JIFFIES. */
> > > > if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
> > > > !krcp->monitor_todo) {
> > > > krcp->monitor_todo = true;
> > > > @@ -3722,7 +3722,7 @@ int rcutree_offline_cpu(unsigned int cpu)
> > > >
> > > > rcutree_affinity_setting(cpu, cpu);
> > > >
> > > > - // nohz_full CPUs need the tick for stop-machine to work quickly
> > > > + /* nohz_full CPUs need the tick for stop-machine to work quickly */
> > > > tick_dep_set(TICK_DEP_BIT_RCU);
> > > > return 0;
> > > > }
> > > > --
> > > > 2.20.1
> > > >