linux-kernel - [PATCH rcu 1/3] srcu: Remove smp_mb() from srcu_read_unlock

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Message-Id: <20241112013143.1926484-1-paulmck@kernel.org>
Date: Mon, 11 Nov 2024 17:31:41 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	rostedt@...dmis.org,
	frederic@...nel.org,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Subject: [PATCH rcu 1/3] srcu: Remove smp_mb() from srcu_read_unlock_lite()

The srcu_read_unlock_lite() function invokes __srcu_read_unlock() instead
of __srcu_read_unlock_lite(), which means that it is doing an unnecessary
smp_mb().  This is harmless other than the performance degradation.

This commit therefore switches to __srcu_read_unlock_lite().

Reported-by: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Closes: https://lore.kernel.org/all/d07e8f4a-d5ff-4c8e-8e61-50db285c57e9@amd.com/
Fixes: c0f08d6b5a61 ("srcu: Add srcu_read_lock_lite() and srcu_read_unlock_lite()")
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>
---
 include/linux/srcu.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 512a8c54ba5ba..fff6265818d4f 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -373,7 +373,7 @@ static inline void srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
 	WARN_ON_ONCE(idx & ~0x1);
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
 	srcu_lock_release(&ssp->dep_map);
-	__srcu_read_unlock(ssp, idx);
+	__srcu_read_unlock_lite(ssp, idx);
 }
 
 /**
-- 
2.40.1