linux-kernel - Re: [PATCH 02/10] writeback: switch to per-bdi threads for flushing data

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Date:	Wed, 08 Jul 2009 07:47:36 +0300
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
CC:	Jens Axboe <jens.axboe@...cle.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, chris.mason@...cle.com,
	david@...morbit.com, hch@...radead.org, akpm@...ux-foundation.org,
	jack@...e.cz, richard@....demon.co.uk, damien.wyart@...e.fr,
	fweisbec@...il.com, Alan.Brunelle@...com
Subject: Re: [PATCH 02/10] writeback: switch to per-bdi threads for flushing
 data

Zhang, Yanmin wrote:
>>> +		list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
>>> +			if (bdi->task || !bdi_has_dirty_io(bdi))
>>> +				continue;
>>> +
>>> +			bdi_add_default_flusher_task(bdi);
>>> +		}
>>> +
>>> +		set_current_state(TASK_INTERRUPTIBLE);
>>> +
>> What happens if we are preempted here? Since we have TASK_INTERRUPTIBLE
>> state, we will not come back unless some other task wakes us up. Who
>> would wake us up in this case?
> If it's preempted (CONFIG_PREEMPT=y), it will stay in runqueue. Only when
> it calls schedule initiatively or calls schedule when exiting to user space,
> it will be moved out of runqueue if its state isn't TASK_RUNNING.
> 
> See flag PREEMPT_ACTIVE.

OK, thanks for the hint!

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)
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