Re: [PATCH 0/3] tools/memory-model, Documentation/litmus-test: Sort out location of litmus test and README

From: Joel Fernandes <joel@joelfernandes.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Akira Yokosawa <akiyks@gmail.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	linux-kernel@vger.kernel.org, vpillai@digitalocean.com,
	Jonathan Corbet <corbet@lwn.net>,
	Alan Stern <stern@rowland.harvard.edu>,
	Andrea Parri <parri.andrea@gmail.com>,
	Will Deacon <will@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Nicholas Piggin <npiggin@gmail.com>,
	David Howells <dhowells@redhat.com>,
	Jade Alglave <j.alglave@ucl.ac.uk>,
	Luc Maranget <luc.maranget@inria.fr>,
	Daniel Lustig <dlustig@nvidia.com>,
	linux-doc@vger.kernel.org
Subject: Re: [PATCH 0/3] tools/memory-model, Documentation/litmus-test: Sort out location of litmus test and README
Date: Mon, 11 May 2020 22:13:09 -0400	[thread overview]
Message-ID: <20200512021309.GA197229@google.com> (raw)
In-Reply-To: <20200511173348.GX2869@paulmck-ThinkPad-P72>

On Mon, May 11, 2020 at 10:33:48AM -0700, Paul E. McKenney wrote:
> On Sun, May 10, 2020 at 04:21:02PM +0900, Akira Yokosawa wrote:
> > On Sat, 9 May 2020 12:43:30 +0900, Akira Yokosawa wrote:
> > > Hi Joel,
> > > 
> > > Sorry for the late response but I've noticed some glitches.
> > >  
> > > On Sun, 22 Mar 2020 21:57:32 -0400, Joel Fernandes (Google) wrote:
> > >> Move MP+onceassign+derefonce to the new Documentation/litmus-tests/rcu/
> > >> directory.
> > > 
> > > MP+onceassign+derefonce.litmus is called out in
> > > tools/memory-model/Documentation/recipes.txt as a representative example
> > > of RCU related litmus test.
> > > 
> > > So I think it should be kept under tools/memory-model/litmus-tests.
> > > 
> > > Further RCU-related litmus tests can be added under Documentation/litmus-tests/.
> > > 
> > > IIUC, this change is not picked up by tip tree yet. So we have time to respin
> > > the series targeting v5.9.
> > > 
> > >>
> > >> More RCU-related litmus tests would be added here.
> > >>
> > >> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > >>
> > >> ---
> > >> Cc: vpillai@digitalocean.com
> > >>
> > >>  Documentation/litmus-tests/README                        | 9 +++++++++
> > > 
> > > Please note that later patches to add atomic litmus tests under
> > > Documentation/litmus-tests/ by Boqun put README as
> > > Documentation/litums-tests/atomic/README.
> > > 
> > > This patch's location of RCU's README as Documentation/litmus-tests/README
> > > looks asymmetric to me.
> > > 
> > > I'm OK with either merging atomic's README with the top-level one or
> > > moving RCU's README to under Documentation/litmus-tests/rcu.
> > > 
> > > Joel, Boqum, can you sort out the location of README?
> > 
> > So something like this?
> > 
> > Patch 1/3 is an independent typo fix in recipes.txt.
> > Patch 2/3 reverts the MP+onceassign+derefonce relocation.
> > Patch 3/3 merges atomic's README into the top-level one.
> > 
> > This is relative to -rcu's lkmm branch.
> > 
> > Thoughts?
> 
> Looks plausible to me, and thank you for reviewing this.
> 
> Joel, thoughts?

Sorry for the delays (OSPM conference in progress). I'm Ok with moving it
back to tools/memory-model/.

I think on top of this patch, I'd like to add a reference to the to the
litmus test in tools/memory-model/ from Documentation/rcu/.

Just to mention my rationale for Documentation/litmus-tests/rcu/, I was
basically looking for a central place for RCU related litmus tests in the
kernel sources and the idea of this new directory came up.

For Akira's series,
Acked-by: Joel Fernandes (Google) <joel@joelfernandes.org>

And could we add the following patch on top of Akira's series so we still
maintain a reference to the moved RCU test?

---8<-----------------------

From 52fdb57551cc769d8bd690f4f2b22de36ddece99 Mon Sep 17 00:00:00 2001
From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
Date: Mon, 11 May 2020 22:06:46 -0400
Subject: [PATCH] docs: litmus-tests: Clarify about the RCU pre-initialization
 test

Since this test was moved to tools/memory-model/, make sure that it is
at least referenced from Documentation/litmus-tests/'s README.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 Documentation/litmus-tests/README | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Documentation/litmus-tests/README b/Documentation/litmus-tests/README
index ac0b270b456c1..53f09e74734a4 100644
--- a/Documentation/litmus-tests/README
+++ b/Documentation/litmus-tests/README
@@ -11,7 +11,6 @@ tools/memory-model/README.
 
 atomic (/atomic derectory)
 --------------------------
-
 Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus
     Test that an atomic RMW followed by a smp_mb__after_atomic() is
     stronger than a normal acquire: both the read and write parts of
@@ -23,8 +22,11 @@ Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
 
 RCU (/rcu directory)
 --------------------
-
 RCU+sync+read.litmus
 RCU+sync+free.litmus
     Both the above litmus tests demonstrate the RCU grace period guarantee
     that an RCU read-side critical section can never span a grace period.
+
+MP+onceassign+derefonce.litmus (moved to tools/memory-model/litmus-tests/)
+   Demonstrates that rcu_assign_pointer() and rcu_dereference() to
+   ensure that an RCU reader will not see pre-initialization garbage.
-- 
2.26.2.645.ge9eca65c58-goog

