Re: [PATCH] rootfs: Use separate mounts lock file

[Baurzhan Ismagulov <ibr@radix50.net>]

On Mon, Jul 26, 2021 at 05:44:26PM +0300, Anton Mikanovich wrote:
> > Definitely a good catch, but I'm still wrapping my head around it. We
> > either have really separated rootfs'es here so that separated lock files
> > are fine, or we rather want rootfs_do_mounts to be locked against
> > buildchroot_do_mounts as well. At least conceptually, even if they well
> > never run in parallel in practice. In that case, MOUNT_LOCKFILE in
> > rootfs.bbclass should be made a weak assignment, to clarify that
> > buildchroot.bbclass will win, irrespective of any ordering.
> > 
> We've performed additional checking and testing of parallel
> mounting/unmounting and didn't find any issues there.
> So I'm pretty sure this should be merged.

To explain the background, we couldn't identify any resource sharing in any
combination of buildchroot and rootfses, so a separate lock has been recently
introduced in e438c8f6 "rootfs: Unmount rootfs mounts if not needed".

This didn't work correctly, as described in the commit message.

Regarding *_do_mounts, they would need to be serialized if mount(8) would have
unlocked shared resources. At least a simple script running 100 mounts and
umounts in parallel didn't reveal any issues.

With kind regards,
Baurzhan.