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-rw-r--r--Documentation/RCU/NMI-RCU.txt13
1 files changed, 7 insertions, 6 deletions
diff --git a/Documentation/RCU/NMI-RCU.txt b/Documentation/RCU/NMI-RCU.txt
index 687777f83b23..881353fd5bff 100644
--- a/Documentation/RCU/NMI-RCU.txt
+++ b/Documentation/RCU/NMI-RCU.txt
@@ -81,18 +81,19 @@ currently executing on some other CPU. We therefore cannot free
up any data structures used by the old NMI handler until execution
of it completes on all other CPUs.
-One way to accomplish this is via synchronize_sched(), perhaps as
+One way to accomplish this is via synchronize_rcu(), perhaps as
follows:
unset_nmi_callback();
- synchronize_sched();
+ synchronize_rcu();
kfree(my_nmi_data);
-This works because synchronize_sched() blocks until all CPUs complete
-any preemption-disabled segments of code that they were executing.
-Since NMI handlers disable preemption, synchronize_sched() is guaranteed
+This works because (as of v4.20) synchronize_rcu() blocks until all
+CPUs complete any preemption-disabled segments of code that they were
+executing.
+Since NMI handlers disable preemption, synchronize_rcu() is guaranteed
not to return until all ongoing NMI handlers exit. It is therefore safe
-to free up the handler's data as soon as synchronize_sched() returns.
+to free up the handler's data as soon as synchronize_rcu() returns.
Important note: for this to work, the architecture in question must
invoke nmi_enter() and nmi_exit() on NMI entry and exit, respectively.