linux-kernel - Re: [PATCH v2] wait while adding MMC host to ensure root mounts

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Message-ID: <8738uubnju.fsf@octavius.laptop.org>
Date:	Sat, 13 Apr 2013 08:52:21 -0400
From:	Chris Ball <cjb@...top.org>
To:	Sergey Yanovich <ynvich@...il.com>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Namjae Jeon <linkinjeon@...il.com>,
	linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org
Subject: Re: [PATCH v2] wait while adding MMC host to ensure root mounts

Hi,

On Sat, Apr 13 2013, Sergey Yanovich wrote:
> On Wed, 2013-03-27 at 07:57 -0400, Chris Ball wrote:
>> If the delay's significant, I agree with you and will revert this patch.
>
> The patch was reverted. The problem is back. Filed bug:
> https://bugzilla.kernel.org/show_bug.cgi?id=56561
>
> A possible solution is to make card a separate device (now only the host
> is a device). In this case, the probing could be done asynchronously
> without breaking the assumption in prepare_namespace().
>
> Chris, could you comment?

The same problem (of requiring rootwait) exists when trying to boot
from a SCSI/USB device, so I don't think there's any MMC-specific
problem here.  Most people who aren't using an initrd have to supply
rootwait.

I liked the idea behind your patch, but the performance regression
isn't acceptable.  If we can't find a way to conditionalize the call
to mmc_flush_scheduled_work() on being in a situation where we're
definitely about to panic, I think the only option would be to try
to come up with a solution at the layers above MMC.

Thanks,

- Chris.
-- 
Chris Ball   <cjb@...top.org>   <http://printf.net/>
One Laptop Per Child
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