linux-kernel - Re: race condition between udevd and modprobe (mtrr

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Date:	Wed, 5 May 2010 07:18:24 +0200
From:	Kay Sievers <kay.sievers@...y.org>
To:	Kyle Hubert <khubert@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: race condition between udevd and modprobe (mtrr_add)

On Tue, May 4, 2010 at 07:30, Kyle Hubert <khubert@...il.com> wrote:
> Hi, while booting an initrd image built off of BusyBox on a thousand
> nodes, we hit a race on a couple of nodes. They hang during the boot
> process with the stack traces listed below. The really simple init
> script in the initrd does a 'udevd --daemon' and then modprobe of a
> device. The device needs to assign an mtrr to the pci resource, and
> instead the whole node hangs. Putting a 'sleep 1' in between these two
> calls prevents any hangs.
>
> mtrr_add_page and the buddy allocator code don't appear to share any
> semaphores, and there isn't an obvious way in which this can hang.
> Possibly the smp_call_function IPI isn't being handled by the other
> cores... That's the best guess. Can anyone help sort this mess out?
>
> Also, is there a better way to test that udevd is fully up? A 'sleep
> 1' is not the preferred solution here.

"udevadm settle" might do it.

Kay
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