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Re: [linux-lvm] [PATCH] lvremove: perform retry logic also on -real subvolume for snapshots



Hi,

This commit is a follow-up on the first change. If the last snapshot of
a volume is removed, the -real subvolume is not removed via the
codepath that has the retry logic, but by just doing a cleanup of
unused volumes. This means that spurious failures may still occur,
although not as often.

These subvolumes should already be properly marked with flags
we attach to them during their creation - these are then sent
encoded in uevent and udev rules are skipped based on it,
including skipping the WATCH udev rule.

Then perhaps it's not udev? I stumbled across the problem myself with
an old version of LVM (it failed like 95% of the time if udisks was
installed, without it failed less often but still quite a bit), then
after a lot of research I found out that this was supposedly fixed in
a current version, I upgraded and then it became rarer but still
occured in around 5% of cases (I had run a script that would create
a snapshot, mount it, umount it and remove the snapshot, all done in
a loop that only stopped on failure). After a *lot* of debugging and
applying the patch I sent here, I couldn't reproduce a single failure
anymore with 2000 tries. (I stopped afterwards, that was good enough
for me.)

..but yes, we could probably add this patch to make sure something
like that does not happen at all.

I'd appreciate it, thanks.

But still it would be better to look why those spurious events
are triggered for non-top-level volumes (it's possible the
OPTIONS:="nowatch" in some case, I'll check...).

I can try to see if I can reproduce it later this week with udevd
running with --debug to see what is going on.

Christian


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