linux-kernel - Re: Fwd: 4.4-rc2 crash: block related

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Message-ID: <5655E22F.6@kernel.dk>
Date:	Wed, 25 Nov 2015 09:30:39 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Jan Kara <jack@...e.cz>,
	Mika Penttilä <mika.penttila@...tfour.com>
Cc:	jack@...e.com, LKML <linux-kernel@...r.kernel.org>,
	Jeff Moyer <jmoyer@...hat.com>
Subject: Re: Fwd: 4.4-rc2 crash: block related

On 11/25/2015 01:39 AM, Jan Kara wrote:
> On Wed 25-11-15 08:27:56, Mika Penttilä wrote:
>> With recent block layer pull i see a 100% repeatable crash on boot while
>> mounting roots (ext4 partition on eMMC, with cfq io scheduler).
>
> Thanks for report! After some investigation I found out we allocate
> elevator specific data in __get_request() only for non-flush requests. And
> this is actually required since the flush machinery uses the space in
> struct request for something else. Doh. So my patch is just wrong and not
> easy to fix since at the time __get_request() is called we are not sure
> whether the flush machinery will be used in the end. Jens, please revert
> 1b2ff19e6a957b1ef0f365ad331b608af80e932e. Thanks!
>
> I'm somewhat surprised that you can reliably hit the race where flushing
> gets disabled for the device just while the request is in flight. But I
> guess during boot it makes some sense.

Yeah, that's impressive. I'll revert it and get it sent up before -rc3 
is cut.

-- 
Jens Axboe

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