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rcu: Add explicit barrier() to __rcu_read_unlock()

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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 <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2021-02-26 11:25:29 -08:00
parent e589c7c723
commit 7e937220af
1 changed files with 2 additions and 1 deletions
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3
kernel/rcu/tree_plugin.h
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@ -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);
}