linux-kernel - Re: [PATCH v7 2/3] sched/task: Add the put_task_struct_atomic

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Message-ID: <cjhvb72qrqggom5gxdjz6mtz3bntlmznx7r52adz72z2t2edzr@hwcog2pltfaq>
Date:   Thu, 4 May 2023 15:21:11 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        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>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Brian Cain <bcain@...cinc.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Christian Brauner <brauner@...nel.org>,
        Andrei Vagin <avagin@...il.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:PERFORMANCE EVENTS SUBSYSTEM" 
        <linux-perf-users@...r.kernel.org>, Hu Chunyu <chuhu@...hat.com>,
        Paul McKenney <paulmck@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v7 2/3] sched/task: Add the put_task_struct_atomic_safe()
 function

On Thu, May 04, 2023 at 05:24:24PM +0200, Peter Zijlstra wrote:
> On Thu, May 04, 2023 at 11:55:15AM -0300, Wander Lairson Costa wrote:
> 
> > > Then I'm thinking something trivial like so:
> > >
> > > static inline void put_task_struct(struct task_struct *t)
> > > {
> > >         if (!refcount_dec_and_test(&t->usage))
> > >                 return;
> > >
> > >         if (IS_ENABLED(CONFIG_PREEMPT_RT) && !preemptible())
> > >                 call_rcu(&t->rcu, __put_task_struct_rcu);
> > >
> > >         __put_task_struct(t);
> > > }
> > >
> > 
> > That's what v5 [1] does. What would be the path in this case? Should I
> > resend it as v8?
> 
> It's almost what v5 does. v5 also has a !in_task() thing. v5 also
> violates codingstyle :-)

IIRC, the in_task() is there because preemptible() doesn't check if it
is running in interrupt context.

> 
> But yeah.. something like that.
>