From 7e937220afa3eada0d4611b31e4e3c60770e39b4 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 26 Feb 2021 11:25:29 -0800 Subject: [PATCH] rcu: Add explicit barrier() to __rcu_read_unlock() Because preemptible RCU's __rcu_read_unlock() is an external function, the rough equivalent of an implicit barrier() is inserted by the compiler. Except that there is a direct call to __rcu_read_unlock() in that same file, and compilers are getting to the point where they might choose to inline the fastpath of the __rcu_read_unlock() function. This commit therefore adds an explicit barrier() to the very beginning of __rcu_read_unlock(). Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_plugin.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 2d603771c7dc..a32494c4b6f6 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -393,8 +393,9 @@ void __rcu_read_unlock(void) { struct task_struct *t = current; + barrier(); // critical section before exit code. if (rcu_preempt_read_exit() == 0) { - barrier(); /* critical section before exit code. */ + barrier(); // critical-section exit before .s check. if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s))) rcu_read_unlock_special(t); }