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-rw-r--r--tools/memory-model/README25
1 files 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