From: Alan Huang <mmpgouride@gmail.com>
To: paulmck@kernel.org, frederic@kernel.org,
neeraj.upadhyay@kernel.org, joel@joelfernandes.org,
josh@joshtriplett.org, boqun.feng@gmail.com, rostedt@goodmis.org,
mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
qiang.zhang1211@gmail.com
Cc: rcu@vger.kernel.org, Alan Huang <mmpgouride@gmail.com>
Subject: [PATCH] rcu: Remove unnecessary READ_ONCE in rcu_preempt_read_enter/exit
Date: Sun, 31 Mar 2024 09:19:32 +0000 [thread overview]
Message-ID: <20240331091932.129617-1-mmpgouride@gmail.com> (raw)
The two READ_ONCEs here imply that there might be updater concurrently
modifies rcu_read_lock_nesting, although it's true there could be
interrupt handlers enter rcu RSCS, but rcu_read_lock_nesting should
remain unchanged after they finished. That is, READ_ONCE and then
WRITE_ONCE the same variable is not a valid pattern, this patch thus
removes the two READ_ONCEs.
Signed-off-by: Alan Huang <mmpgouride@gmail.com>
---
kernel/rcu/tree_plugin.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 340bbefe5f65..c90edbb7fa40 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -376,12 +376,12 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
static void rcu_preempt_read_enter(void)
{
- WRITE_ONCE(current->rcu_read_lock_nesting, READ_ONCE(current->rcu_read_lock_nesting) + 1);
+ WRITE_ONCE(current->rcu_read_lock_nesting, current->rcu_read_lock_nesting + 1);
}
static int rcu_preempt_read_exit(void)
{
- int ret = READ_ONCE(current->rcu_read_lock_nesting) - 1;
+ int ret = current->rcu_read_lock_nesting - 1;
WRITE_ONCE(current->rcu_read_lock_nesting, ret);
return ret;
--
2.34.1
next reply other threads:[~2024-03-31 9:19 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-31 9:19 Alan Huang [this message]
2024-04-09 20:10 ` [PATCH] rcu: Remove unnecessary READ_ONCE in rcu_preempt_read_enter/exit Paul E. McKenney
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