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authorPaul E. McKenney <paul.mckenney@linaro.org>2011-06-27 00:17:43 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-09-28 21:38:22 -0700
commite4cc1f22b2f4e9b0207a8cdb63e56dcf99e82d35 (patch)
treeec3fad6587f0a83e764a571394bdfb85a84edf30 /kernel/rcutree.h
parentd4c08f2ac311a360230eef7e5395b0ec8d8f0670 (diff)
rcu: Simplify quiescent-state accounting
There is often a delay between the time that a CPU passes through a quiescent state and the time that this quiescent state is reported to the RCU core. It is quite possible that the grace period ended before the quiescent state could be reported, for example, some other CPU might have deduced that this CPU passed through dyntick-idle mode. It is critically important that quiescent state be counted only against the grace period that was in effect at the time that the quiescent state was detected. Previously, this was handled by recording the number of the last grace period to complete when passing through a quiescent state. The RCU core then checks this number against the current value, and rejects the quiescent state if there is a mismatch. However, one additional possibility must be accounted for, namely that the quiescent state was recorded after the prior grace period completed but before the current grace period started. In this case, the RCU core must reject the quiescent state, but the recorded number will match. This is handled when the CPU becomes aware of a new grace period -- at that point, it invalidates any prior quiescent state. This works, but is a bit indirect. The new approach records the current grace period, and the RCU core checks to see (1) that this is still the current grace period and (2) that this grace period has not yet ended. This approach simplifies reasoning about correctness, and this commit changes over to this new approach. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcutree.h')
-rw-r--r--kernel/rcutree.h6
1 files changed, 3 insertions, 3 deletions
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index d11a0065321..51638b68b2d 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -230,9 +230,9 @@ struct rcu_data {
/* in order to detect GP end. */
unsigned long gpnum; /* Highest gp number that this CPU */
/* is aware of having started. */
- unsigned long passed_quiesc_completed;
- /* Value of completed at time of qs. */
- bool passed_quiesc; /* User-mode/idle loop etc. */
+ unsigned long passed_quiesce_gpnum;
+ /* gpnum at time of quiescent state. */
+ bool passed_quiesce; /* User-mode/idle loop etc. */
bool qs_pending; /* Core waits for quiesc state. */
bool beenonline; /* CPU online at least once. */
bool preemptible; /* Preemptible RCU? */