linux-kernel - [PATCH v5 05/18] rcu: Move trace_rcu

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Date:   Thu,  1 Sep 2022 22:17:07 +0000
From:   "Joel Fernandes (Google)" <joel@...lfernandes.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, rushikesh.s.kadam@...el.com,
        urezki@...il.com, neeraj.iitr10@...il.com, frederic@...nel.org,
        paulmck@...nel.org, rostedt@...dmis.org, vineeth@...byteword.org,
        boqun.feng@...il.com,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>
Subject: [PATCH v5 05/18] rcu: Move trace_rcu_callback() before bypassing

If any CB is queued into the bypass list, then trace_rcu_callback() does
not show it. This makes it not clear when a callback was actually
queued, as you only end up getting a trace_rcu_invoke_callback() trace.
Fix it by moving trace_rcu_callback() before
trace_rcu_nocb_try_bypass().

Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 kernel/rcu/tree.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 5ec97e3f7468..9fe581be8696 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2809,10 +2809,7 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func)
 	}
 
 	check_cb_ovld(rdp);
-	if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags))
-		return; // Enqueued onto ->nocb_bypass, so just leave.
-	// If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock.
-	rcu_segcblist_enqueue(&rdp->cblist, head);
+
 	if (__is_kvfree_rcu_offset((unsigned long)func))
 		trace_rcu_kvfree_callback(rcu_state.name, head,
 					 (unsigned long)func,
@@ -2821,6 +2818,11 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func)
 		trace_rcu_callback(rcu_state.name, head,
 				   rcu_segcblist_n_cbs(&rdp->cblist));
 
+	if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags))
+		return; // Enqueued onto ->nocb_bypass, so just leave.
+	// If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock.
+	rcu_segcblist_enqueue(&rdp->cblist, head);
+
 	trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued"));
 
 	/* Go handle any RCU core processing required. */
-- 
2.37.2.789.g6183377224-goog