linux-kernel - Re: [PATCH 06/11] rcu: clear t->rcu_read_unlock

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Date:   Fri, 1 Nov 2019 05:10:56 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Lai Jiangshan <laijs@...ux.alibaba.com>
Cc:     linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org
Subject: Re: [PATCH 06/11] rcu: clear t->rcu_read_unlock_special in one go

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@...ux.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@...ux.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@...ux.alibaba.com>
    Signed-off-by: Paul E. McKenney <paulmck@...nel.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