linux-kernel - [PATCH tip/core/rcu 07/21] rcu: Make rcu_future_needs_gp() check all ->need_future

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Date:   Sun, 22 Apr 2018 20:03:30 -0700
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, joel.opensrc@...il.com,
        torvalds@...ux-foundation.org, npiggin@...il.com,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 07/21] rcu: Make rcu_future_needs_gp() check all ->need_future_gps[] elements

Currently, the rcu_future_needs_gp() function checks only the current
element of the ->need_future_gps[] array, which might miss elements that
were offset from the expected element, for example, due to races with
the start or the end of a grace period.  This commit therefore makes
rcu_future_needs_gp() use the need_any_future_gp() macro to check all
of the elements of this array.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 2 +-
 kernel/rcu/tree.h | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index afc5e32f0da4..b05ab6379562 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -720,7 +720,7 @@ static int rcu_future_needs_gp(struct rcu_state *rsp)
 	struct rcu_node *rnp = rcu_get_root(rsp);
 
 	lockdep_assert_irqs_disabled();
-	return READ_ONCE(need_future_gp_element(rnp, rnp->completed));
+	return need_any_future_gp(rnp);
 }
 
 /*
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 952cd0c223fe..123c30eac8b5 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -169,7 +169,8 @@ struct rcu_node {
 	bool __nonzero = false;						\
 									\
 	for (__i = 0; __i < ARRAY_SIZE((rnp)->need_future_gp); __i++)	\
-		__nonzero = __nonzero || (rnp)->need_future_gp[__i];	\
+		__nonzero = __nonzero ||				\
+			    READ_ONCE((rnp)->need_future_gp[__i]);	\
 	__nonzero;							\
 })
 
-- 
2.5.2