linux-kernel - [PATCH tip/core/rcu 10/10] rcu: Account for rcu_all_qs() in cond

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Message-Id: <1512156104-20104-10-git-send-email-paulmck@linux.vnet.ibm.com>
Date:   Fri,  1 Dec 2017 11:21:44 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 10/10] rcu: Account for rcu_all_qs() in cond_resched()

If cond_resched() returns false, then it has already invoked
rcu_all_qs().  This is also invoked (now redundantly) by
rcu_note_voluntary_context_switch().  This commit therefore changes
cond_resched_rcu_qs() to invoke rcu_note_voluntary_context_switch_lite()
instead of rcu_note_voluntary_context_switch() to avoid the redundant
invocation of rcu_all_qs().

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 include/linux/rcupdate.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index a6ddc42f87a5..7bd8b5a6db10 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -197,7 +197,7 @@ static inline void exit_tasks_rcu_finish(void) { }
 #define cond_resched_rcu_qs() \
 do { \
 	if (!cond_resched()) \
-		rcu_note_voluntary_context_switch(current); \
+		rcu_note_voluntary_context_switch_lite(current); \
 } while (0)
 
 /*
-- 
2.5.2