What does 'lock order reversal' mean?

Jon Noack noackjr at alumni.rice.edu
Fri Apr 9 04:13:17 PDT 2004

On 4/9/2004 5:04 AM, Artem Koutchine wrote:
> When i run test perl scripts (6 processes in parallel)
> which crate a big array, manupulate it, free and over again
> so 2GB of ram is used up and system starts using swap i see 
> the message below (only onces). What does it mean?
> Apr  7 20:16:34 new kernel: lock order reversal
> Apr  7 20:16:34 new kernel: 1st 0xc79446b4 vm object (vm object) @
> /usr/src/sys/vm/swap_pager.c:1313
> Apr  7 20:16:35 new kernel: 2nd 0xc08b9e00 swap_pager swhash (swap_pager
> swhash) @ /usr/src/sys/vm/swap_pager.c:1803
> Apr  7 20:16:35 new kernel: 3rd 0xc7898294 vm object (vm object) @
> /usr/src/sys/vm/uma_core.c:886

This is:
1) A FAQ.
2) A false positive.
3) Completely harmless.

Previously reported to the list:
1) 04/07/2004 (by you)
2) 03/31/2004
3) 03/28/2004
4) 03/24/2004
5) 03/22/2004
6) 03/18/2004
7) ...

For a good explanation of lock order reversals:

I'll put up a webpage of false-positives if someone will commit a change 
in the LOR warning to point to it (or something similar to this):
"lock order reversal: please see http://example.com for status before 

I still think it would be best if this page were on the FreeBSD website, 
but I'll host it if necessary.

Jon Noack

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