linux-kernel - [PATCH tip/core/rcu 14/24] rcu: Add READ_ONCE() to rcu_do_batch() access to rcu_cpu_stall_ftrace

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Message-Id: <20200831180116.32690-14-paulmck@kernel.org>
Date:   Mon, 31 Aug 2020 11:01:06 -0700
From:   paulmck@...nel.org
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, 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@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH tip/core/rcu 14/24] rcu: Add READ_ONCE() to rcu_do_batch() access to rcu_cpu_stall_ftrace_dump

From: "Paul E. McKenney" <paulmck@...nel.org>

Given that sysfs can change the value of rcu_cpu_stall_ftrace_dump at any
time, this commit adds a READ_ONCE() to the accesses to that variable.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree_stall.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index a1780a6..0fde39b 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -623,7 +623,7 @@ static void check_cpu_stall(struct rcu_data *rdp)
 
 		/* We haven't checked in, so go dump stack. */
 		print_cpu_stall(gps);
-		if (rcu_cpu_stall_ftrace_dump)
+		if (READ_ONCE(rcu_cpu_stall_ftrace_dump))
 			rcu_ftrace_dump(DUMP_ALL);
 
 	} else if (rcu_gp_in_progress() &&
@@ -632,7 +632,7 @@ static void check_cpu_stall(struct rcu_data *rdp)
 
 		/* They had a few time units to dump stack, so complain. */
 		print_other_cpu_stall(gs2, gps);
-		if (rcu_cpu_stall_ftrace_dump)
+		if (READ_ONCE(rcu_cpu_stall_ftrace_dump))
 			rcu_ftrace_dump(DUMP_ALL);
 	}
 }
-- 
2.9.5