linux-kernel - Re: [PATCH v2 1/2] maple_tree: Disable mas_wr_append() when other readers are possible

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Message-ID: <20230912141732.k5l37d4xeiwssaln@revolver>
Date:   Tue, 12 Sep 2023 10:17:32 -0400
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        maple-tree@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org,
        Shanker Donthineni <sdonthineni@...dia.com>
Subject: Re: [PATCH v2 1/2] maple_tree: Disable mas_wr_append() when other
 readers are possible

* Matthew Wilcox <willy@...radead.org> [230912 10:10]:
> On Mon, Sep 11, 2023 at 07:54:52PM -0400, Liam R. Howlett wrote:
> > Taking the mutex lock in kernel/irq/manage.c __setup_irq() is calling a
> > cond_resched().
> > 
> > >From what Michael said [1] in this thread, since something has already
> > set TIF_NEED_RESCHED, it will eventually enable interrupts on us.
> > 
> > I've traced this to running call_rcu() in kernel/rcu/tiny.c and
> > is_idle_task(current) is true, which means rcu runs:
> > 		/* force scheduling for rcu_qs() */                                                                     
> >                 resched_cpu(0);
> > 
> > the task is set idle in sched_init() -> init_idle() and never changed,
> > afaict.
> 
> Should calling init_idle() be deferred until after interrupts are
> all set up?

At this point it is not platform specific code so I don't know what kind
of fallout I'll produce with a change like that, but I was wondering if
the thread running the boot process is really 'idle'?