linux-kernel - Re: [PATCH 1/4] base/drivers/arch

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Message-ID: <20181030083308.5znognajpwjvdxfv@vireshk-i7>
Date:   Tue, 30 Oct 2018 14:03:08 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH 1/4] base/drivers/arch_topology: Remove useless check

On 30-10-18, 08:55, Daniel Lezcano wrote:
> The workqueue is called from init_cpu_capacity_callback(). This one is
> called in the notifier callback. IOW the notification callback
> unregisters itself. But if it is not registered, it won't unregister,
> hence it won't call the workqueue and init_cpu_capacity_notifier() is
> not called.

Sorry, couldn't understand most of your reply :)

Though let me try to explain the problem I was trying to show you..

cpufreq-notifier-callback
        -> init_cpu_capacity_callback()
                -> free raw capacity
                -> queue_work() to unregister the notifier
                -> return

        ->init_cpu_capacity_callback() called again before work was processed.
                -> If we don't check raw_capacity, we may end up using
                NULL pointer, as the notifier isn't unregistered yet.

-- 
viresh