linux-kernel - [PATCH next v2 1/5] locking/osq_lock: Defer clearing node->locked until the slow osq

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Message-ID: <714ca2e587cf4cd485ae04e5afb8d5bb@AcuMS.aculab.com>
Date: Sun, 31 Dec 2023 21:51:20 +0000
From: David Laight <David.Laight@...LAB.COM>
To: "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'peterz@...radead.org'" <peterz@...radead.org>, "'longman@...hat.com'"
	<longman@...hat.com>
CC: "'mingo@...hat.com'" <mingo@...hat.com>, "'will@...nel.org'"
	<will@...nel.org>, "'boqun.feng@...il.com'" <boqun.feng@...il.com>, "'Linus
 Torvalds'" <torvalds@...ux-foundation.org>,
	"'virtualization@...ts.linux-foundation.org'"
	<virtualization@...ts.linux-foundation.org>, 'Zeng Heng'
	<zengheng4@...wei.com>
Subject: [PATCH next v2 1/5] locking/osq_lock: Defer clearing node->locked
 until the slow osq_lock() path.

Since node->locked cannot be set before the assignment to prev->next
it is save to clear it in the slow path.

Signed-off-by: David Laight <david.laight@...lab.com>
---
 kernel/locking/osq_lock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index 75a6f6133866..e0bc74d85a76 100644
--- a/kernel/locking/osq_lock.c
+++ b/kernel/locking/osq_lock.c
@@ -97,7 +97,6 @@ bool osq_lock(struct optimistic_spin_queue *lock)
 	int curr = encode_cpu(smp_processor_id());
 	int old;
 
-	node->locked = 0;
 	node->next = NULL;
 	node->cpu = curr;
 
@@ -111,6 +110,7 @@ bool osq_lock(struct optimistic_spin_queue *lock)
 	if (old == OSQ_UNLOCKED_VAL)
 		return true;
 
+	node->locked = 0;
 	prev = decode_cpu(old);
 	node->prev = prev;
 
-- 
2.17.1

-
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