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References: <20210104152058.36642-1-frederic@kernel.org> <20210104152058.36642-4-frederic@kernel.org>
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From:   Fabio Estevam <festevam@gmail.com>
Date:   Mon, 4 Jan 2021 12:57:47 -0300
Message-ID: <CAOMZO5ChFtTj0O0RVxmq-pX8acuvvGhL4ON4bu9fvwBqj_fyrQ@mail.gmail.com>
Subject: Re: [PATCH 3/4] ARM: imx6q: Fix missing need_resched() check after rcu_idle_enter()
To:     Frederic Weisbecker <frederic@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Ingo Molnar <mingo@kernel.org>,
        stable <stable@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Len Brown <lenb@kernel.org>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        NXP Linux Team <linux-imx@nxp.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>
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Hi Frederic,

On Mon, Jan 4, 2021 at 12:21 PM Frederic Weisbecker <frederic@kernel.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?