linux-kernel - [PATCH v2 2/3] locking/rwsem: disable preemption for spinning region

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Date:   Wed, 13 Oct 2021 21:41:53 +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 v2 2/3] locking/rwsem: disable preemption for spinning region

The spinning region rwsem_spin_on_owner() should not be preempted,
however the rwsem_down_write_slowpath() invokes it and don't disable
preemption. Fix it by adding a pair of preempt_disable/enable().

Signed-off-by: Yanfei Xu <yanfei.xu@...driver.com>
---
 kernel/locking/rwsem.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 7b5af452ace2..06925b43c3e7 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -1024,6 +1024,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
 	enum writer_wait_state wstate;
 	struct rwsem_waiter waiter;
 	struct rw_semaphore *ret = sem;
+	enum owner_state owner_state;
 	DEFINE_WAKE_Q(wake_q);
 
 	/* do optimistic spinning and steal lock if possible */
@@ -1099,9 +1100,13 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
 		 * In this case, we attempt to acquire the lock again
 		 * without sleeping.
 		 */
-		if (wstate == WRITER_HANDOFF &&
-		    rwsem_spin_on_owner(sem) == OWNER_NULL)
-			goto trylock_again;
+		if (wstate == WRITER_HANDOFF) {
+			preempt_disable();
+			owner_state = rwsem_spin_on_owner(sem);
+			preempt_enable();
+			if (owner_state == OWNER_NULL)
+				goto trylock_again;
+		}
 
 		/* Block until there are no active lockers. */
 		for (;;) {
-- 
2.27.0