From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
mingo@kernel.org
Cc: stern@rowland.harvard.edu, parri.andrea@gmail.com,
will.deacon@arm.com, peterz@infradead.org, boqun.feng@gmail.com,
npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk,
luc.maranget@inria.fr, willy@infradead.org,
"Paul E. McKenney" <paulmck@linux.ibm.com>
Subject: [PATCH RFC LKMM 4/7] tools/memory-model: Update README for addition of SRCU
Date: Wed, 9 Jan 2019 13:07:45 -0800 [thread overview]
Message-ID: <20190109210748.29074-4-paulmck@linux.ibm.com> (raw)
In-Reply-To: <20190109210706.GA27268@linux.ibm.com>
This commit updates the section on LKMM limitations to no longer say
that SRCU is not modeled, but instead describe how LKMM's modeling of
SRCU departs from the Linux-kernel implementation.
TL;DR: There is no known valid use case that cares about the Linux
kernel's ability to have partially overlapping SRCU read-side critical
sections.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Acked-by: Andrea Parri <andrea.parri@amarulasolutions.com>
---
tools/memory-model/README | 25 +++++++++++++++++++++++--
1 file changed, 23 insertions(+), 2 deletions(-)
diff --git a/tools/memory-model/README b/tools/memory-model/README
index 0f2c366518c6..9d7d4f23503f 100644
--- a/tools/memory-model/README
+++ b/tools/memory-model/README
@@ -221,8 +221,29 @@ The Linux-kernel memory model has the following limitations:
additional call_rcu() process to the site of the
emulated rcu-barrier().
- e. Sleepable RCU (SRCU) is not modeled. It can be
- emulated, but perhaps not simply.
+ e. Although sleepable RCU (SRCU) is now modeled, there
+ are some subtle differences between its semantics and
+ those in the Linux kernel. For example, the kernel
+ might interpret the following sequence as two partially
+ overlapping SRCU read-side critical sections:
+
+ 1 r1 = srcu_read_lock(&my_srcu);
+ 2 do_something_1();
+ 3 r2 = srcu_read_lock(&my_srcu);
+ 4 do_something_2();
+ 5 srcu_read_unlock(&my_srcu, r1);
+ 6 do_something_3();
+ 7 srcu_read_unlock(&my_srcu, r2);
+
+ In contrast, LKMM will interpret this as a nested pair of
+ SRCU read-side critical sections, with the outer critical
+ section spanning lines 1-7 and the inner critical section
+ spanning lines 3-5.
+
+ This difference would be more of a concern had anyone
+ identified a reasonable use case for partially overlapping
+ SRCU read-side critical sections. For more information,
+ please see: https://paulmck.livejournal.com/40593.html
f. Reader-writer locking is not modeled. It can be
emulated in litmus tests using atomic read-modify-write
--
2.17.1
next prev parent reply other threads:[~2019-01-09 21:08 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-09 21:07 [PATCH RFC memory-model 0/6] LKMM updates Paul E. McKenney
2019-01-09 21:07 ` [PATCH RFC LKMM 1/7] tools/memory-model: Rename some RCU relations Paul E. McKenney
2019-01-09 21:07 ` [PATCH RFC LKMM 2/7] tools/memory-model: Refactor " Paul E. McKenney
2019-01-09 21:07 ` [PATCH RFC LKMM 3/7] tools/memory-model: Add SRCU support Paul E. McKenney
2019-01-09 21:07 ` Paul E. McKenney [this message]
2019-01-09 21:07 ` [PATCH RFC LKMM 5/7] docs/memory-barriers.txt: Enforce heavy ordering for port I/O accesses Paul E. McKenney
2019-01-11 9:53 ` Peter Zijlstra
2019-02-11 15:30 ` Will Deacon
2019-02-11 17:11 ` Arnd Bergmann
2019-02-11 17:32 ` Will Deacon
2019-01-09 21:07 ` [PATCH RFC LKMM 6/7] tools/memory-model: Update Documentation/explanation.txt to include SRCU support Paul E. McKenney
2019-01-09 21:07 ` [PATCH RFC LKMM 7/7] tools/memory-model: Dynamically check SRCU lock-to-unlock matching Paul E. McKenney
2019-01-10 9:41 ` Andrea Parri
2019-01-10 14:40 ` Paul E. McKenney
2019-01-10 23:20 ` Andrea Parri
2019-01-11 21:44 ` Paul E. McKenney
2019-01-11 21:57 ` Alan Stern
2019-01-09 23:18 ` [PATCH RFC memory-model 0/6] LKMM updates Andrea Parri
2019-01-09 23:40 ` Paul E. McKenney
2019-01-10 0:39 ` Andrea Parri
2019-01-10 4:20 ` Paul E. McKenney
2019-01-10 8:40 ` Andrea Parri
2019-01-10 14:31 ` Paul E. McKenney
2019-01-10 15:41 ` Alan Stern
2019-01-10 16:31 ` Paul E. McKenney
2019-01-10 22:46 ` Andrea Parri
2019-01-10 15:47 ` Alan Stern
2019-01-10 19:03 ` Paul E. McKenney
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