linux-kernel - Re: [PATCH 3/4] ARM: imx6q: Fix missing need_resched() check after rcu_idle

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Message-ID: <CAOMZO5ChFtTj0O0RVxmq-pX8acuvvGhL4ON4bu9fvwBqj_fyrQ@mail.gmail.com>
Date:   Mon, 4 Jan 2021 12:57:47 -0300
From:   Fabio Estevam <festevam@...il.com>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        stable <stable@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>
Subject: Re: [PATCH 3/4] ARM: imx6q: Fix missing need_resched() check after rcu_idle_enter()

Hi Frederic,

On Mon, Jan 4, 2021 at 12:21 PM Frederic Weisbecker <frederic@...nel.org> wrote:
>
> Entering RCU idle mode may cause a deferred wake up of an RCU NOCB_GP
> kthread (rcuog) to be serviced.
>
> Usually a wake up happening while running the idle task is spotted in
> one of the need_resched() checks carefully placed within the idle loop
> that can break to the scheduler.
>
> Unfortunately imx6q_enter_wait() is beyond the last generic
> need_resched() check and it performs a wfi right away after the call to
> rcu_idle_enter(). We may halt the CPU with a resched request unhandled,
> leaving the task hanging.
>
> Fix this with performing a last minute need_resched() check after
> calling rcu_idle_enter().

Shouldn't tif_need_resched() be used instead of need_resched() in the
commit log?