[Libguestfs] supermin root: race condition with multiple drives

[Richard W.M. Jones]

On Tue, Jul 13, 2021 at 02:05:48PM +0100, Brian Candler wrote:
> Hi,
> 
> I discovered an issue when using libguestfs with large numbers of
> attached disks.  I submitted the details to github:
> 
> https://github.com/libguestfs/libguestfs/issues/69
> 
> ... and then discovered that the mailing list is the right place,
> not github.  Sorry about that!
> 
> The problem is: I have batches of 40 or 50 qcow2 images to write
> files to.  It is very slow to start a separate libguestfs appliance
> for each one, so what I do is to start a single one with 40 or 50
> disks attached, and then mount, upload and unmount each one in turn.
> 
> What I find is that sometimes the disks are attached in the wrong
> order, such that the kernel tries to use one of these qcow2 files as
> its root disk, instead of the supermin appliance image.  This seems
> to happen more often when the system is under load, such as when
> running multiple libguestfs instances concurrently (I have 15 or 20
> different versions of these batches of 40-50 disks to create, so to
> speed things up, I run them concurrently).

It could be this issue:

https://bugzilla.redhat.com/show_bug.cgi?id=1804207

Fixed in libguestfs 1.42.0 (commit bca9b94fc59377 and others).

Rich.

> This is all "userland" stuff so ought to work fine under load, but
> the supermin kernel booting issue messes it up intermittently.
> 
> Anyway, the github ticket has full details, including standalone
> scripts which can reproduce the problem on my system.  I'd be
> grateful if someone could take a look.
> 
> Many thanks,
> 
> Brian Candler.
> 
> 
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-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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