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Date: Sat, 21 Jan 2012 00:04:23 +0900
Message-ID: <CAKYAXd-OzSsNgTakm_6Dq4p5C4KViBH6ctdXDO7tfkn=XrE8xA@mail.gmail.com>
Subject: Re: [PATCHv2] backing-dev: fix wakeup timer races with bdi_unregister()
From: Namjae Jeon <linkinjeon@gmail.com>
To: Rabin Vincent <rabin@rab.in>
Cc: fengguang.wu@intel.com, axboe@kernel.dk, linux-kernel@vger.kernel.org,
        chanho0207@gmail.com
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>
> After this patch, this is what wakeup_timer_fn looks like:
>
> static void wakeup_timer_fn(unsigned long data)
> {
>        struct backing_dev_info *bdi = (struct backing_dev_info *)data;
>
>        spin_lock_bh(&bdi->wb_lock);
>        if (bdi->wb.task) {
>                trace_writeback_wake_thread(bdi);
>                wake_up_process(bdi->wb.task);
>        } else if (bdi->dev) {
>                /*
>                 * When bdi tasks are inactive for long time, they are killed.
>                 * In this case we have to wake-up the forker thread which
>                 * should create and run the bdi thread.
>                 */
>                trace_writeback_wake_forker_thread(bdi);
>                wake_up_process(default_backing_dev_info.wb.task);
>        }
>        spin_unlock_bh(&bdi->wb_lock);
> }
>
> So how will trace_writeback_wake_forker_thread() be called if bdi->dev is NULL?
>
> This patch added the if (bdi->dev) check, perhaps you overlooked that?

Hi Rabin.
I clearly understand. Thanks for your explanation.

Reviewed-by: Namjae Jeon <linkinjeon@gmail.com>