Re: LOR (vm object - swap_pager swhash)

On 07/01/04 06:02, Jon Noack wrote:
> On 07/01/04 05:47, Jon Noack wrote:
>> Perhaps the best bet is to add a FAQ.  The FAQ would point to Bjoern's 
>> site and the LOR-message would point to the FAQ entry.
> 
> Again, my docproj foo is weak, but see the attached FAQ.

You have to uninstall the xhtml-1.1 port to get docproj to work?!? 
Whatever...

In any case, here's what it would look like:
http://www.noacks.org/freebsd/book.html#LOCK-ORDER-REVERSAL

Updated patch attached.

Jon

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> 
>       <qandaentry>
>         <question id="lock-order-reversal">
>           <para>What is a <errorname>lock order reversal</errorname>?</para>
>         </question>
> 
>         <answer>
>           <para>&a.rwatson; answered this question very succinctly on
>             the freebsd-current list in a thread entitled <quote><ulink
>             url="http://docs.freebsd.org/cgi/getmsg.cgi?fetch=65165+0+/usr/local/www/db/text/2003/freebsd-current/20031221.freebsd-current">lock
>             order reversals - what do they mean?</ulink></quote>  
> 
>           <blockquote>
>             <attribution>&a.rwatson; on freebsd-current, December 14,
>               2003</attribution>
> 
>             <para>These warnings are generated by Witness, a run-time lock
>               diagnostic system found in FreeBSD 5-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's worth
>               observing that Witness is actually slightly conservative, and so
>               it's possible to get false positives.  In the event that Witness
>               is accurately reporting a lock order problem, it's 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 added locking, as lock order reversals usually
>               get fixed pretty quickly because Witness is busy generating
>               warnings :-).</para>
>           </blockquote>
> 
>           <note>
>             <para>See <ulink
>               url="http://sources.zabbadoz.net/freebsd/lor.html">Bjoern
>               Zeeb's lock order reversal page</ulink> for the status of
>               known lock order reversals.</para>
>           </note>
>         </answer>
>       </qandaentry>