Re: [PATCH memory-model 7/8] tools/memory-model: Add documentation about SRCU read-side critical sections

Andrea Parri
2023-03-22T01:41:00Z

On Mon, Mar 20, 2023 at 06:02:45PM -0700, Paul E. McKenney wrote:
> From: Alan Stern <stern@rowland.harvard.edu>
>
> Expand the discussion of SRCU and its read-side critical sections in
> the Linux Kernel Memory Model documentation file explanation.txt. The
> new material discusses recent changes to the memory model made in
> commit 6cd244c87428 ("tools/memory-model: Provide exact SRCU
> semantics").

How about squashing the diff below (adjusting subject and changelog):

Andrea

diff --git a/tools/memory-model/Documentation/litmus-tests.txt b/tools/memory-model/Documentation/litmus-tests.txt
index 26554b1c5575e..acac527328a1f 100644
--- a/tools/memory-model/Documentation/litmus-tests.txt
+++ b/tools/memory-model/Documentation/litmus-tests.txt
@@ -1028,32 +1028,7 @@ Limitations of the Linux-kernel memory model (LKMM) include:
additional call_rcu() process to the site of the
emulated rcu-barrier().

- 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
- on the trickiness of such overlapping, please see:
- https://paulmck.livejournal.com/40593.html
-
- f. Reader-writer locking is not modeled. It can be
+ e. Reader-writer locking is not modeled. It can be
emulated in litmus tests using atomic read-modify-write
operations.

Andrea