linux-kernel - [PATCH] rcu: Trace cbs accelerated without leaf rnp node lock held

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Date:   Mon, 11 Jan 2021 17:15:43 +0530
From:   Neeraj Upadhyay <neeraju@...eaurora.org>
To:     paulmck@...nel.org, josh@...htriplett.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        joel@...lfernandes.org
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        Neeraj Upadhyay <neeraju@...eaurora.org>
Subject: [PATCH] rcu: Trace cbs accelerated without leaf rnp node lock held

Trace cbs which are accelerated without rnp lock help in
rcu_accelerate_cbs_unlocked().

Signed-off-by: Neeraj Upadhyay <neeraju@...eaurora.org>
---
 kernel/rcu/tree.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 338b817..097990a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1473,6 +1473,17 @@ static void rcu_gp_kthread_wake(void)
 	swake_up_one(&rcu_state.gp_wq);
 }
 
+static void rcu_trace_accelerated_cbs(struct rcu_data *rdp,
+				      unsigned long gp_seq_req)
+{
+	rcu_lockdep_assert_cblist_protected(rdp);
+	/* Trace depending on how much we were able to accelerate. */
+	if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
+		trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccWaitCB"));
+	else
+		trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB"));
+}
+
 /*
  * If there is room, assign a ->gp_seq number to any callbacks on this
  * CPU that have not already been assigned.  Also accelerate any callbacks
@@ -1511,12 +1522,7 @@ static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
 	if (!rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req))
 		return ret;
 	ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
-
-	/* Trace depending on how much we were able to accelerate. */
-	if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
-		trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccWaitCB"));
-	else
-		trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB"));
+	rcu_trace_accelerated_cbs(rdp, gp_seq_req);
 
 	return ret;
 }
@@ -1538,7 +1544,8 @@ static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp,
 	c = rcu_seq_snap(&rcu_state.gp_seq);
 	if (!READ_ONCE(rdp->gpwrap) && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
 		/* Old request still live, so mark recent callbacks. */
-		(void)rcu_segcblist_accelerate(&rdp->cblist, c);
+		if (rcu_segcblist_accelerate(&rdp->cblist, c))
+			rcu_trace_accelerated_cbs(rdp, c);
 		return;
 	}
 	raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
-- 
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