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

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Date:   Tue, 11 Dec 2018 10:18:31 +1100
From:   Oliver <oohall@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Russell Currey <ruscur@...sell.cc>,
        Sam Bobroff <sbobroff@...ux.ibm.com>,
        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 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?

>
> 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
>