linux-kernel - Re: [3.8-rc3 -> 3.8-rc4 regression] Re: [PATCH] module, async: async_synchronize

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Message-ID: <CAKA=qzbyPxU8sBRbYzL61VS6R_o5p+2RdPogJ0nOmQ8NBi2GSA@mail.gmail.com>
Date:	Tue, 3 Dec 2013 08:28:43 -0600
From:	Josh Hunt <joshhunt00@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jonathan Nieder <jrnieder@...il.com>,
	Ming Lei <ming.lei@...onical.com>,
	Alex Riesen <raa.lkml@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Jens Axboe <axboe@...nel.dk>,
	USB list <linux-usb@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [3.8-rc3 -> 3.8-rc4 regression] Re: [PATCH] module, async:
 async_synchronize_full() on module init iff async is used

On Tue, Nov 26, 2013 at 4:29 PM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Tue, Nov 26, 2013 at 04:12:41PM -0600, Josh Hunt wrote:
>> I should have clarified that I'm not using dm/md in my setup. I know
>> the modules are getting loaded in the log I attached, but root is not
>> a md/dm device.
>
> Can you please still try it?  The init script is broken and we're now
> just trying to restore just enough of the old behavior so that the
> issue is not exposed.  The boot script in use seems to load md/dm
> modules after storage drivers and use their termination as the signal
> for "storage ready", so it could be a good enough bandaid even if
> you're not using dm/md.
>
> Thanks.
>
> --
> tejun

Tejun

You're right. Thanks for pointing this out. I did not realize there
was a bug in the init script. The version of initramfs-tools I was
using had the following bug:
https://bugs.launchpad.net/ubuntu/+source/initramfs-tools/+bug/1215911

Updating to 0.99ubuntu13.4 of initramfs-tools resolved my boot hangs.

I did try using the workaround as suggested by Linus. In my setup the
dm_init() code was hit, however it still appeared to be too late at
times. I also tried moving the call to async_synchronize_full() above
the for loop and it still had the same issue (patch attached.) Out of
around 10 reboot tests it failed to find root 1 or 2 times.

The ubuntu scripts don't ever actually call do_mount() if it can't
find the device. It seems to rely on some udev functionality to tell
it when the device is present, and if that fails it just bails out.

This change has introduced a regression. However, I only noticed it
b/c my init script had a bug which caused it not to wait around for
the device to appear.

-- 
Josh

View attachment "async-dbg.patch" of type "text/x-patch" (1773 bytes)