Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 12 Jun 2023 22:02:29 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Boqun Feng <boqun.feng@gmail.com>
Cc:     torvalds@linux-foundation.org, keescook@chromium.org,
        gregkh@linuxfoundation.org, pbonzini@redhat.com,
        masahiroy@kernel.org, nathan@kernel.org, ndesaulniers@google.com,
        nicolas@fjasle.eu, catalin.marinas@arm.com, will@kernel.org,
        vkoul@kernel.org, trix@redhat.com, ojeda@kernel.org,
        mingo@redhat.com, longman@redhat.com, dennis@kernel.org,
        tj@kernel.org, cl@linux.com, acme@kernel.org, mark.rutland@arm.com,
        alexander.shishkin@linux.intel.com, jolsa@kernel.org,
        namhyung@kernel.org, irogers@google.com, adrian.hunter@intel.com,
        juri.lelli@redhat.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com,
        paulmck@kernel.org, frederic@kernel.org, quic_neeraju@quicinc.com,
        joel@joelfernandes.org, josh@joshtriplett.org,
        mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
        rientjes@google.com, vbabka@suse.cz, roman.gushchin@linux.dev,
        42.hyeyoo@gmail.com, apw@canonical.com, joe@perches.com,
        dwaipayanray1@gmail.com, lukas.bulwahn@gmail.com,
        john.johansen@canonical.com, paul@paul-moore.com,
        jmorris@namei.org, serge@hallyn.com, linux-kbuild@vger.kernel.org,
        linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org,
        llvm@lists.linux.dev, linux-perf-users@vger.kernel.org,
        rcu@vger.kernel.org, linux-security-module@vger.kernel.org,
        tglx@linutronix.de, ravi.bangoria@amd.com, error27@gmail.com,
        luc.vanoostenryck@gmail.com
Subject: Re: [PATCH v3 08/57] sched: Simplify wake_up_if_idle()
Message-ID: <20230612200229.GN4253@hirez.programming.kicks-ass.net>
References: <20230612090713.652690195@infradead.org>
 <20230612093537.977924652@infradead.org>
 <ZIddtMiTj8Kktq1z@boqun-archlinux>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <ZIddtMiTj8Kktq1z@boqun-archlinux>
Precedence: bulk

On Mon, Jun 12, 2023 at 11:02:28AM -0700, Boqun Feng wrote:
> On Mon, Jun 12, 2023 at 11:07:21AM +0200, Peter Zijlstra wrote:
> > Use guards to reduce gotos and simplify control flow.
> > 
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> >  kernel/sched/core.c  |   20 ++++++--------------
> >  kernel/sched/sched.h |   15 +++++++++++++++
> >  2 files changed, 21 insertions(+), 14 deletions(-)
> > 
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -3872,21 +3872,13 @@ static void __ttwu_queue_wakelist(struct
> >  void wake_up_if_idle(int cpu)
> >  {
> >  	struct rq *rq = cpu_rq(cpu);
> > -	struct rq_flags rf;
> >  
> > -	rcu_read_lock();
> > -
> > -	if (!is_idle_task(rcu_dereference(rq->curr)))
> > -		goto out;
> > -
> > -	rq_lock_irqsave(rq, &rf);
> > -	if (is_idle_task(rq->curr))
> > -		resched_curr(rq);
> > -	/* Else CPU is not idle, do nothing here: */
> > -	rq_unlock_irqrestore(rq, &rf);
> > -
> > -out:
> > -	rcu_read_unlock();
> > +	guard(rcu)();
> > +	if (is_idle_task(rcu_dereference(rq->curr))) {
> > +		guard(rq_lock)(rq);
> 
> We assume that irq must be disabled when this function called?
> Otherwise, I don't understand why this is not
> 
> 	guard(rq_lock_irqsave)(rq);
> 

You're quite right, I messed that up.