linux-kernel - Re: [PATCH] powerpc: eeh_event: convert semaphore to completion

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Date:   Tue, 11 Dec 2018 10:33:01 +1100
From:   Sam Bobroff <sbobroff@...ux.ibm.com>
To:     Oliver <oohall@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Russell Currey <ruscur@...sell.cc>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, aik@...abs.ru,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powerpc: eeh_event: convert semaphore to completion

On Tue, Dec 11, 2018 at 10:18:31AM +1100, Oliver wrote:
> On Tue, Dec 11, 2018 at 8:52 AM Arnd Bergmann <arnd@...db.de> wrote:
> >
> > For this use case, completions and semaphores are equivalent,
> > but semaphores are an awkward interface that should generally
> > be avoided, so use the completion instead.
> 
> IIRC Sam has been reworking the locking used inside of EEH so this is
> probably going to clash with his changes. Converting to a completion
> is probably a good idea, but we might want to do it as a part of his
> series since it's going to collide with this anyway.
> 
> Sam, what do you think?

It's such a small change, I don't think it will cause any problems for
the rework. Anyway it seems like a good change, so I'd prefer to see it
go in :-)

Cheers,
Sam.

> >
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > ---
> >  arch/powerpc/kernel/eeh_event.c | 9 +++------
> >  1 file changed, 3 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/powerpc/kernel/eeh_event.c b/arch/powerpc/kernel/eeh_event.c
> > index 61c9356bf9c9..227e57f980df 100644
> > --- a/arch/powerpc/kernel/eeh_event.c
> > +++ b/arch/powerpc/kernel/eeh_event.c
> > @@ -35,7 +35,7 @@
> >   */
> >
> >  static DEFINE_SPINLOCK(eeh_eventlist_lock);
> > -static struct semaphore eeh_eventlist_sem;
> > +static DECLARE_COMPLETION(eeh_eventlist_event);
> >  static LIST_HEAD(eeh_eventlist);
> >
> >  /**
> > @@ -55,7 +55,7 @@ static int eeh_event_handler(void * dummy)
> >         struct eeh_pe *pe;
> >
> >         while (!kthread_should_stop()) {
> > -               if (down_interruptible(&eeh_eventlist_sem))
> > +               if (wait_for_completion_interruptible(&eeh_eventlist_event))
> >                         break;
> >
> >                 /* Fetch EEH event from the queue */
> > @@ -102,9 +102,6 @@ int eeh_event_init(void)
> >         struct task_struct *t;
> >         int ret = 0;
> >
> > -       /* Initialize semaphore */
> > -       sema_init(&eeh_eventlist_sem, 0);
> > -
> >         t = kthread_run(eeh_event_handler, NULL, "eehd");
> >         if (IS_ERR(t)) {
> >                 ret = PTR_ERR(t);
> > @@ -142,7 +139,7 @@ int eeh_send_failure_event(struct eeh_pe *pe)
> >         spin_unlock_irqrestore(&eeh_eventlist_lock, flags);
> >
> >         /* For EEH deamon to knick in */
> > -       up(&eeh_eventlist_sem);
> > +       complete(&eeh_eventlist_event);
> >
> >         return 0;
> >  }
> > --
> > 2.20.0
> >
> 

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