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Date: Fri, 4 Dec 2015 16:34:43 -0800 From: Josh Triplett <josh@...htriplett.org> To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com Subject: Re: [PATCH tip/core/rcu 1/8] documentation: Record RCU requirements The content of the document seems fine; a few comments below on meta-issues. On Fri, Dec 04, 2015 at 03:50:19PM -0800, Paul E. McKenney wrote: > --- /dev/null > +++ b/Documentation/RCU/Design/Requirements/Requirements.html > @@ -0,0 +1,2799 @@ > +<!-- DO NOT HAND EDIT. --> > +<!-- Instead, edit Requirements.htmlx and run 'sh htmlqqz.sh Requirements' --> > +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" > + "http://www.w3.org/TR/html4/loose.dtd"> Nit: these days, this should just be: <!doctype html> > + <html> > + <head><title>A Tour Through RCU's Requirements [LWN.net]</title> > + <meta HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> Is there a good reason to not use charset=utf-8 here? > + > +<h1>A Tour Through RCU's Requirements</h1> > + > +<p>Copyright IBM Corporation, 2015</p> If you're aiming for a properly formatted copyright notice, the year typically comes first, followed by the copyright holder. That said, your corporate guidelines presumably have a specific format; is this that format? > +<p>Author: Paul E. McKenney</p> > +<p><i>The initial version of this document appeared in the > +<a href="http://lwn.net/">LWN</a> articles > +<a href="http://lwn.net/Articles/652156/">here</a>, > +<a href="http://lwn.net/Articles/652677/">here</a>, and > +<a href="http://lwn.net/Articles/653326/">here</a>.</i></p> s/http/https/g > +<p> > +All that aside, here are the categories of currently known RCU requirements: > +</p> > + > +<ol> > +<li> <a href="#Fundamental Requirements"> Anchors don't typically have spaces in them. This may work in some browsers, but it doesn't validate. You should either use %20 or (better) use a '-'. > +<p> > +This is followed by a <a href="#Summary">summary</a>, > +which is in turn followed by the inevitable > +<a href="#Answers to Quick Quizzes">answers to the quick quizzes</a>. (Note: when editing anchors, don't forget to handle the target of this in the generation script.) > +<p> > +This scenario resembles one of the first uses of RCU in > +<a href="http://en.wikipedia.org/wiki/DYNIX">DYNIX/ptx</a>, s/http/https/ > +<p> > +However, this temptation must be resisted because there are a > +surprisingly large number of ways that the compiler > +(to say nothing of > +<a href="http://www.openvms.compaq.com/wizard/wiz_2637.html">DEC Alpha CPUs</a>) This link sadly doesn't seem to work anymore; it redirects to HP's general page on OpenVMS, not a copy of that specific article.o Use this instead, assuming no current live version exists: https://web.archive.org/web/20120720095054/http://www.openvms.compaq.com/wizard/wiz_2637.html > +<li> It is also easy to forget to use <tt>rcu_assign_pointer()</tt> > + and <tt>rcu_dereference()</tt>, perhaps (incorrectly) > + substituting a simple assignment. > + To catch this sort of error, a given RCU-protected pointer may be > + tagged with <tt>__rcu</tt>, after which running sparse > + with <tt>CONFIG_SPARSE_RCU_POINTER=y</tt> will complain > + about simple-assignment accesses to that pointer. > + Arnd Bergmann made me aware of this requirement, and also > + supplied the needed > + <a href="http://lwn.net/Articles/376011/">patch series</a>. s/http/https/ > +<li> Open-coded use of <tt>rcu_assign_pointer()</tt> and > + <tt>rcu_dereference()</tt> to create typical linked > + data structures can be surprisingly error-prone. > + Therefore, RCU-protected > + <a href="http://lwn.net/Articles/609973/#RCU List APIs">linked lists</a> s/http/https/ > +<p> > +This all should be quite obvious, but the fact remains that > +Linus Torvalds recently had to > +<a href="http://marc.info/?l=linux-kernel&m=142905739823385">remind</a> > +me of this requirement. I'd suggest using the lkml.kernel.org redirector for this link, along with a Message-Id. > +<p> > +The name notwithstanding, some Linux-kernel architectures > +can have nested NMIs, which RCU must handle correctly. > +Andy Lutomirski > +<a href="https://lkml.org/lkml/2014/11/21/642">surprised me</a> > +with this requirement; > +he also kindly surprised me with > +<a href="https://lkml.org/lkml/2014/11/22/1">an algorithm</a> > +that meets this requirement. These links should both use lkml.kernel.org as well. Doubly important because lkml.org is often down or has broken messages in its archive. > +<p> > +RCU therefore provides > +<tt><a href="http://lwn.net/Articles/217484/">rcu_barrier()</a></tt>, s/http/https/ > +<p> > +This pair of mutual scheduler-RCU requirements came as a > +<a href="http://lwn.net/Articles/453002/">complete surprise</a>. s/http/https/ > +This requirement made its presence known after users made it > +clear that an earlier > +<a href="http://lwn.net/Articles/107930/">real-time patch</a> s/http/https/ > +did not meet their needs, in conjunction with some > +<a href="https://lkml.org/lkml/2005/3/17/199">RCU issues</a> lkml.kernel.org > +<p> > +The > +<a href="http://lwn.net/Articles/609973/#RCU Per-Flavor API Table">RCU-bh API</a> s/http/https/ (and the same for all later lwn links in the document) - Josh Triplett -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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