Three LOR with latest -current

[Benjamin Kaduk]

Hello John,

These seem to be well-known, per
http://ipv4.sources.zabbadoz.net/freebsd/lor.html

On Tue, 16 Aug 2011, John wrote:

> Hi folks,
>
>   I'm seeing 3 lock order reversals with an up-to-date -current
> system. Stock system, GENERIC kernel. Let me know if this isn't
> enough information. Just booting the system and the dmesg.
>
> Thanks,
> John
>
>
> lock order reversal:
> 1st 0xfffffe0289627db8 ufs (ufs) @ /usr/src.2011-08-14_10.53pm_EDT/sys/ufs/ffs/ffs_snapshot.c:425
> 2nd 0xffffff9f0db49778 bufwait (bufwait) @ /usr/src.2011-08-14_10.53pm_EDT/sys/kern/vfs_bio.c:2658
> 3rd 0xfffffe00404a8098 ufs (ufs) @ /usr/src.2011-08-14_10.53pm_EDT/sys/ufs/ffs/ffs_snapshot.c:546

This looks like #285.

>
>
> lock order reversal:
> 1st 0xffffff9f0db49778 bufwait (bufwait) @ /usr/src.2011-08-14_10.53pm_EDT/sys/kern/vfs_bio.c:2658
> 2nd 0xfffffe004034dcb0 snaplk (snaplk) @ /usr/src.2011-08-14_10.53pm_EDT/sys/ufs/ffs/ffs_snapshot.c:818

The line numbers are a bit off, but this could be #269.

>
>
> lock order reversal:
> 1st 0xfffffe004034dcb0 snaplk (snaplk) @ /usr/src.2011-08-14_10.53pm_EDT/sys/kern/vfs_vnops.c:301
> 2nd 0xfffffe0289627db8 ufs (ufs) @ /usr/src.2011-08-14_10.53pm_EDT/sys/ufs/ffs/ffs_snapshot.c:1620

And this would be #240.

Since they are so commonly reported (but no deadlocks have been attributed 
to them), it seems likely that they are harmless.
Perhaps we should tell WITNESS to not warn about them ...

-Ben Kaduk