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

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Date:   Fri, 5 May 2023 10:29:16 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Wander Lairson Costa <wander@...hat.com>,
        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>,
        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 Fri, 5 May 2023 10:26:02 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> > > IIRC, the in_task() is there because preemptible() doesn't check if it
> > > is running in interrupt context.    
> > 
> > #define preemptible()   (preempt_count() == 0 && !irqs_disabled())
> > 
> > When in interrupt context preempt_count() will have a non-zero value in
> > HARDIRQ_MASK and IRQs must be disabled, so preemptible() evaluates to
> > (false && false), last time I checked that ends up being false.  
> 
> Interesting, I can't find v5 anywhere in my mail folders (but I have
> v4 and v6!). Anyway, from just the context of this email, and seeing
> IS_ENABLED(CONFIG_PREEMPT_RT), I'm guessing that in_task() returns false if
> it's running in a interrupt thread, where preemtible() does not.

But then I question, does it matter if it is running in an interrupt thread
or not for put_task_struct()?

-- Steve