Robert Watson answered this question very succinctly on the freebsd-current list in a thread entitled lock order reversals – what do they mean?
These warnings are generated by Witness, a run-time lock diagnostic system found in FreeBSD -CURRENT kernels (but removed in releases). You can read more about Witness in the witness(4) man page, which talks about its capabilities. Among other things, Witness performs run-time lock order verification using a combination of hard coded lock orders, and run-time detected lock orders, and generates console warnings when lock orders are violated. The intent of this is to detect the potential for deadlocks due to lock order violations; it is worth observing that Witness is actually slightly conservative, and so it is possible to get false positives. In the event that Witness is accurately reporting a lock order problem, it is basically saying “If you were unlucky, a deadlock would have happened here”. There are a couple of “well known” false positives, which we need to do a better job of documenting to prevent spurious reports. The non-well-known ones typically correspond to bugs in newly ad
Related Questions
- Dear Jamie: There is a magazine in Canada entitled "Sales Promotion" that publishing a list of all the incentive/novelty suppliers in Canada including a list of all products supplied by category and by province. The magazine is published every two months.
- Robert Watson
- I’ve got a question about the Wait List that wasn’t answered here. What do I do?
