linux-kernel - [PATCH tip/core/rcu 11/21] tracepoint: Remove smp_read_barrier

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Message-Id: <1512157876-24665-11-git-send-email-paulmck@linux.vnet.ibm.com>
Date:   Fri,  1 Dec 2017 11:51:06 -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 11/21] tracepoint: Remove smp_read_barrier_depends() from comment

The comment in tracepoint_add_func() mentions smp_read_barrier_depends(),
whose use should be quite restricted.  This commit updates the comment
to instead mention the smp_store_release() and rcu_dereference_sched()
that the current code actually uses.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...nel.org>
Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
---
 kernel/tracepoint.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 685c50ae6300..671b13457387 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -212,11 +212,10 @@ static int tracepoint_add_func(struct tracepoint *tp,
 	}
 
 	/*
-	 * rcu_assign_pointer has a smp_wmb() which makes sure that the new
-	 * probe callbacks array is consistent before setting a pointer to it.
-	 * This array is referenced by __DO_TRACE from
-	 * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
-	 * is used.
+	 * rcu_assign_pointer has as smp_store_release() which makes sure
+	 * that the new probe callbacks array is consistent before setting
+	 * a pointer to it.  This array is referenced by __DO_TRACE from
+	 * include/linux/tracepoint.h using rcu_dereference_sched().
 	 */
 	rcu_assign_pointer(tp->funcs, tp_funcs);
 	if (!static_key_enabled(&tp->key))
-- 
2.5.2