rcu: Add READ_ONCE() to rcu_do_batch() access to rcu_cpu_stall_ftrace_dump

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@kernel.org>

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index a1780a6..0fde39b 100644 (file)
--- 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);
        }
 }