linux-kernel - Re: [PATCH 2/5] sched: always use blk_schedule_flush_plug in io_schedule

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Message-ID: <x49383g189d.fsf@segfault.boston.devel.redhat.com>
Date:	Fri, 01 May 2015 14:07:42 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Shaohua Li <shli@...com>
Cc:	<linux-kernel@...r.kernel.org>, <axboe@...com>, <hch@....de>,
	<neilb@...e.de>
Subject: Re: [PATCH 2/5] sched: always use blk_schedule_flush_plug in io_schedule_out

Jeff Moyer <jmoyer@...hat.com> writes:

> Shaohua Li <shli@...com> writes:
>
>> block plug callback could sleep, so we introduce a parameter
>> 'from_schedule' and corresponding drivers can use it to destinguish a
>> schedule plug flush or a plug finish. Unfortunately io_schedule_out
>> still uses blk_flush_plug(). This causes below output (Note, I added a
>> might_sleep() in raid1_unplug to make it trigger faster, but the whole
>> thing doesn't matter if I add might_sleep). In raid1/10, this can cause
>> deadlock.
>>
>> This patch makes io_schedule_out always uses blk_schedule_flush_plug.
>> This should only impact drivers (as far as I know, raid 1/10) which are
>> sensitive to the 'from_schedule' parameter.
>
> Why wouldn't you change io_schedule_timeout to use blk_flush_plug_list
> instead?

Sorry, I did not fully engage my brain on this one.  I see that's
exactly what you did.

I'll add my reviewed-by once you've addressed hch's concern.

Cheers,
Jeff
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