docs/174226: [patch] faq: lock-order-reversal

[Bas Smeelen]

>Number:         174226
>Category:       docs
>Synopsis:       [patch] faq: lock-order-reversal
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-doc
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          update
>Submitter-Id:   current-users
>Arrival-Date:   Thu Dec 06 11:50:00 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator:     Bas Smeelen
>Release:        9.1
>Organization:
>Environment:
FreeBSD cfd 9.1-RELEASE FreeBSD 9.1-RELEASE #1 r243880: Wed Dec  5 08:15:54 CET 2012     root at cfd:/usr/obj/usr/src/sys/GENERIC  i386
>Description:

>How-To-Repeat:

>Fix:
Index: book.xml
===================================================================
--- book.xml	(revision 40280)
+++ book.xml	(working copy)
@@ -3488,9 +3488,20 @@
 	</question>
 
 	<answer>
-	  <para>An answer for this question can be found in the &os;
-	    Glossary, see <ulink
-	      url="&url.books.handbook;/freebsd-glossary.html#lor-glossary">LOR</ulink>.</para>
+	  <para>The &os; kernel uses a number of resource locks to
+	    arbitrate contention for those resources.  A run-time
+	    lock diagnostic system found in &os.current; kernels
+	    (but removed for releases), called &man.witness.4;,
+	    detects the potential for deadlocks due to locking errors.
+	    (&man.witness.4; is actually slightly conservative, so
+	    it is possible to get false positives.)  A true positive
+	    report indicates that <quote>if you were unlucky, a deadlock would
+	    have happened here</quote>.</para>
+
+	  <para>True positive LORs tend to get fixed quickly, so
+	    check &a.current.url; and the
+	    <ulink url="http://sources.zabbadoz.net/freebsd/lor.html">LORs Seen
+	    </ulink> page before posting to the mailing lists.</para>
 	</answer>
       </qandaentry>


>Release-Note:
>Audit-Trail:
>Unformatted: