Re: race condition in md creation?

[Stijn Hoop <stijn@sandcat.nl>]

Hi,

On Sat, 28 May 2011 07:24:40 +1000
NeilBrown <neilb@suse.de> wrote:
> On Fri, 27 May 2011 15:20:57 +0200 Stijn Hoop <stijn@sandcat.nl>
> wrote:
> 
> > Hello,
> > 
> > while creating a test suite for internal purposes I ran into a race
> > condition where a (very small) raid array that was just created
> > cannot be stopped.
> > 
> > mdadm --create succeeds, but the subsequent mdadm --stop reports
> > 'Device or resource busy'.
> > 
> > Please see the attached script for reproduction purposes, partial
> > output from a run on my system (Fedora 14, kernel
> > 2.6.35.13-91.fc14.x86_64, mdadm-3.1.3-0.git20100804.2.fc14.x86_64):
> > 
> > 
> > 5+0 records in
> > 5+0 records out
> > 5242880 bytes (5.2 MB) copied, 0.0166663 s, 315 MB/s
> > 5+0 records in
> > 5+0 records out
> > 5242880 bytes (5.2 MB) copied, 0.0197533 s, 265 MB/s
> > mdadm: array /dev/md0 started.
> > mdadm: failed to stop array /dev/md0: Device or resource busy
> > Perhaps a running process, mounted filesystem or active volume
> > group? failed to stop /dev/md0, sleep 1 sec then retrying one more
> > time mdadm: stopped /dev/md0
> 
> When a new device appears (such as  a new md array), udev springs in
> to action and examines it to see if it should do something with it.
> While udev (or some tool that it ran) is examining the md array it
> looks like it is busy so an attempt to stop it will fail.
> 
> My test scripts tend to have
>    udevadm settle
> before
>    mdadm --stop
> 
> for exactly this reason.

Ah, that makes perfect sense. Thanks for the explanation!

--Stijn