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[dm-devel] Snapshot handover working, yippee!, was Re: semop failed for cookie?



Ok, so my complaining about code-progress should now be complete. I think I'm back in action. But the "BUG: lock held when returning to user space" still seems like a message you folks wanted yourselves to hear.

After grumbling to myself that fedora doesn't provide a package with dmsetup.static, I went ahead and copied all relocatable deps (/lib/ld-linux.so.2??) to tmpfs along with dmsetup, using LD_LIBRARY_PATH. I also used --noudevrules and --noudevsync. Then I followed the documentation I found which, for use cases as esoteric as mine, might be desirable in snapshot.txt

https://patchwork.kernel.org/patch/59806/

I.e. rules for snapshot handover in the general case. (who knows, maybe I'll be the only user of non-snapshot-merge snapshot handover for all time) (though technically I guess you can call what I've been doing for the last several years to be an alternate form of snapshot merging. I.e. where your snapshot base is readonly and you are merging both the readonly base and cow to a third writable device)

Anyway, I finally got my stuffs working again, or at least, I have a virtual snapshot-as-rootfs being dm-mirror migrated right now. I assume that my loading of a new table, is sufficiently equivalent to the dmsetup remove of the old snapshot as described in the above link.

But finally, and the real reason for this message- during this I noticed that the aforementioned "BUG:" was not in fact what was killing my system. I.e. I still get that message, though everything else appears to work and it appears to be harmless (I hope).

BUG: lock held when returning to user space!

dmsetup/865 is leaving the kernel with locks still held!
1 lock held by dmsetup/865:
 #0:   (&journal->j_barrier){+.+...+}, at: [<c056b84d>] jbd2_journal_lock_\
updates+0xbd/0xc5

Thanks again for putting up with my corner case complaints.

Cheers,

-dmc


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