Attachment 44266 Details for Bug 68595 – lor-faq.diff

[patch] lor-faq.diff

lor-faq.diff (text/plain), 2.80 KB, created by Jon Noack on 2004-07-02 09:40:13 UTC

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Creator: Jon Noack

Created: 2004-07-02 09:40:13 UTC

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>Index: book.sgml
>===================================================================
>RCS file: /home/ncvs/doc/en_US.ISO8859-1/books/faq/book.sgml,v
>retrieving revision 1.626
>diff -u -r1.626 book.sgml
>--- book.sgml	1 Jul 2004 07:29:04 -0000	1.626
>+++ book.sgml	1 Jul 2004 11:29:35 -0000
>@@ -4379,6 +4379,51 @@
>             channel is numbered 0, and so on.</para>
>         </answer>
>       </qandaentry>
>+
>+      <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></para>
>+
>+          <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
>+              &man.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>
>     </qandaset>
>   </chapter>

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