linux-kernel - Re: [RFC PATCH 01/11] locking/ww_mutex: Remove wakeups from under mutex::wait

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Message-ID: <CALE1s+PPhC0Eb5Eojz+H5m96OXdc5qp6eOhj16vZgsP9n_UX1A@mail.gmail.com>
Date:   Thu, 20 Oct 2022 11:43:23 -0700
From:   "Connor O'Brien" <connoro@...gle.com>
To:     Waiman Long <longman@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        John Stultz <jstultz@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Qais Yousef <qais.yousef@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: Re: [RFC PATCH 01/11] locking/ww_mutex: Remove wakeups from under mutex::wait_lock

On Tue, Oct 4, 2022 at 9:01 AM Waiman Long <longman@...hat.com> wrote:
>
> On 10/3/22 17:44, Connor O'Brien wrote:
> > diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h
> > index 56f139201f24..dfc174cd96c6 100644
> > --- a/kernel/locking/ww_mutex.h
> > +++ b/kernel/locking/ww_mutex.h
> > @@ -161,6 +161,11 @@ static inline void lockdep_assert_wait_lock_held(struct rt_mutex *lock)
> >
> >   #endif /* WW_RT */
> >
> > +void ww_ctx_wake(struct ww_acquire_ctx *ww_ctx)
> > +{
> > +     wake_up_q(&ww_ctx->wake_q);
> > +}
> > +
> >   /*
> >    * Wait-Die:
> >    *   The newer transactions are killed when:
> > @@ -284,7 +289,7 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
> >   #ifndef WW_RT
> >               debug_mutex_wake_waiter(lock, waiter);
> >   #endif
> > -             wake_up_process(waiter->task);
> > +             wake_q_add(&ww_ctx->wake_q, waiter->task);
> >       }
> >
> >       return true;
> > @@ -331,7 +336,7 @@ static bool __ww_mutex_wound(struct MUTEX *lock,
> >                * wakeup pending to re-read the wounded state.
> >                */
> >               if (owner != current)
> > -                     wake_up_process(owner);
> > +                     wake_q_add(&ww_ctx->wake_q, owner);
> >
> >               return true;
> >       }
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index ee28253c9ac0..617e737392be 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1013,6 +1013,13 @@ void wake_up_q(struct wake_q_head *head)
> >               wake_up_process(task);
> >               put_task_struct(task);
> >       }
> > +     /*
> > +      * XXX connoro: seems this is needed now that ww_ctx_wake() passes in a
> > +      * wake_q_head that is embedded in struct ww_acquire_ctx rather than
> > +      * declared locally.
> > +      */
> > +     head->first = node;
> > +     head->lastp = &head->first;
> >   }
> >
>
> You shouldn't do wake_q_init() here in wake_up_q(). Instead, you should
> do it in ww_ctx_wake() right after the wake_up_q() call.

Thanks, will fix this in the next version.

>
> Cheers,
> Longman
>