linux-kernel - [PATCH 2/2] locking/rwsem: add preempt

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Date:   Tue, 28 Sep 2021 00:38:47 +0800
From:   Yanfei Xu <yanfei.xu@...driver.com>
To:     peterz@...radead.org, mingo@...hat.com, will@...nel.org,
        longman@...hat.com, boqun.feng@...il.com
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] locking/rwsem: add preempt_disable/enable for spin region

The rwsem_optimistic_spin() invokes the rwsem_spin_on_owner() with
preemption disabled, but rwsem_down_write_slowpath() doesn't. Because
the spin region should not be preempted, add preempt_disable/enable()
in rwsem_spin_on_owner().

Signed-off-by: Yanfei Xu <yanfei.xu@...driver.com>
---
 kernel/locking/rwsem.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 2907f9d8e4a6..db3a6a06a9c8 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -674,6 +674,7 @@ rwsem_spin_on_owner(struct rw_semaphore *sem)
 	if (state != OWNER_WRITER)
 		return state;
 
+	preempt_disable();
 	rcu_read_lock();
 	for (;;) {
 		/*
@@ -704,6 +705,7 @@ rwsem_spin_on_owner(struct rw_semaphore *sem)
 		cpu_relax();
 	}
 	rcu_read_unlock();
+	preempt_enable();
 
 	return state;
 }
-- 
2.27.0