Re: [Xen-devel] Block script unsafe when starting multiple devices in parallel

[Marek Marczykowski <marmarek@xxxxxxxxxxxx>]

On 30.08.2011 19:37, Nathan March wrote:
> Hi Guys,
> 
> Ran into an issue where losetup was failing, added some logging to it's
> executions to see (first #'s are parent pid / pid):
> 
> 32435 / 32438 - losetup -f
> 32436 / 32439 - losetup -f
> 32435 / 32438 -  Exit code: 0
> 32435 / 32438 -  Output: /dev/loop/10
> 32436 / 32439 -  Exit code: 0
> 32436 / 32439 -  Output: /dev/loop/10
> 32128 / 32451 - losetup /dev/loop/10 /mnt/xenDisks2/nathanxen2/backup_tmp
> 31934 / 32452 - losetup /dev/loop/10 /mnt/xenDisks1/nathanxen2/swap
> 
> Sometime's losetup seems to be stuck waiting on something else and since
> multiple block devices are brought up in parallel, the block script
> tries to use the same name for multiple loopback devices.

This should be prevented by locking mechanism (claim_lock /
release_lock), but it isn't working in some cases
(http://lists.xensource.com/archives/html/xen-devel/2011-07/msg00182.html).

I've workarounded it with wrapping this script with flock (in udev rules).

Perhaps it can be done in tools/hotplug/Linux/xen-backend.rules instead
of using claim_lock/release_lock? This is much simpler than
restructuring all hotplug scripts...

-- 
Pozdrawiam / Best Regards,
Marek Marczykowski         | RLU #390519
marmarek at mimuw edu pl   | xmpp:marmarek at staszic waw pl

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