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Date:   Tue, 16 May 2023 14:05:55 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Wander Lairson Costa <wander@redhat.com>,
        Oleg Nesterov <oleg@redhat.com>,
        "Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>,
        Brian Cain <bcain@quicinc.com>,
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        Stafford Horne <shorne@gmail.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        "Liam R. Howlett" <Liam.Howlett@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>,
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        Andrei Vagin <avagin@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Daniel Bristot de Oliveira <bristot@kernel.org>,
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        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Luis Goncalves <lgoncalv@redhat.com>
Subject: Re: [PATCH v9] kernel/fork: beware of __put_task_struct calling
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        <ZGPYVAF6Nkp2umaa@casper.infradead.org>
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On Tue, 16 May 2023 20:24:04 +0100 Matthew Wilcox <willy@infradead.org> wrote:

> On Tue, May 16, 2023 at 04:14:41PM -0300, Wander Lairson Costa wrote:
> > +void __put_task_struct_rcu_cb(struct rcu_head *rhp)
> > +{
> > +	struct task_struct *task = container_of(rhp, struct task_struct, rcu);
> > +
> > +	__put_task_struct(task);
> > +}
> > +EXPORT_SYMBOL_GPL(__put_task_struct_rcu_cb);
> 
> Why does this need to be exported when its only caller is within the
> main kernel and cannot possibly be built as a module?

It's referenced by inlined put_task_struct(), which is called from all
over.

However I believe the above definition could be inside #ifdef
CONFIG_PREEMPT_RT, to save a scrap of resources?