rcu: Make force_quiescent_state() start grace period if needed
Grace periods cannot be started while force_quiescent_state() is
active. This is OK in that the affected CPUs will try again
later, but it does induce needless grace-period delays. This
patch causes rcu_start_gp() to record a failed attempt to start
a grace period. When force_quiescent_state() prepares to return,
it then starts the grace period if there was such a failed
attempt.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12626465501854-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index edb6fae..bd5d78ad 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -278,6 +278,11 @@
/* Force QS state. */
u8 fqs_active; /* force_quiescent_state() */
/* is running. */
+ u8 fqs_need_gp; /* A CPU was prevented from */
+ /* starting a new grace */
+ /* period because */
+ /* force_quiescent_state() */
+ /* was running. */
long gpnum; /* Current gp number. */
long completed; /* # of last completed gp. */