Re: [PATCH 06/11] rcu: clear t->rcu_read_unlock_special in one go

Paul E. McKenney
2019-11-01T12:10:58Z

On Thu, Oct 31, 2019 at 10:08:01AM +0000, Lai Jiangshan wrote:
> Clearing t->rcu_read_unlock_special in one go makes the code
> more clearly.
>
> Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>

Nice simplification! I had to hand-apply it due to not having taken the
earlier patches, plus I redid the commit log. Could you please check
the version shown below?

Thanx, Paul

------------------------------------------------------------------------

commit 0bef7971edbbd35ed4d1682a465f682077981e85
Author: Lai Jiangshan <laijs@linux.alibaba.com>
Date: Fri Nov 1 05:06:21 2019 -0700

rcu: Clear ->rcu_read_unlock_special only once

In rcu_preempt_deferred_qs_irqrestore(), ->rcu_read_unlock_special is
cleared one piece at a time. Given that the "if" statements in this
function use the copy in "special", this commit removes the clearing
of the individual pieces in favor of clearing ->rcu_read_unlock_special
in one go just after it has been determined to be non-zero.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 8d0e8c1..d113923 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -444,11 +444,9 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
local_irq_restore(flags);
return;
}
- t->rcu_read_unlock_special.b.exp_hint = false;
- t->rcu_read_unlock_special.b.deferred_qs = false;
+ t->rcu_read_unlock_special.s = 0;
if (special.b.need_qs) {
rcu_qs();
- t->rcu_read_unlock_special.b.need_qs = false;
if (!t->rcu_read_unlock_special.s && !rdp->exp_deferred_qs) {
local_irq_restore(flags);
return;
@@ -471,7 +469,6 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)

/* Clean up if blocked during RCU read-side critical section. */
if (special.b.blocked) {
- t->rcu_read_unlock_special.b.blocked = false;

/*
* Remove this task from the list it blocked on. The task