linux-kernel - [tip: locking/core] locking/rtmutex: Fix incorrect condition in rtmutex_spin_on

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Message-ID: <163982167017.23020.3158863463249807527.tip-bot2@tip-bot2>
Date:   Sat, 18 Dec 2021 10:01:10 -0000
From:   "tip-bot2 for Zqiang" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Zqiang <qiang1.zhang@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>, stable@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: locking/core] locking/rtmutex: Fix incorrect condition in
 rtmutex_spin_on_owner()

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     8f556a326c93213927e683fc32bbf5be1b62540a
Gitweb:        https://git.kernel.org/tip/8f556a326c93213927e683fc32bbf5be1b62540a
Author:        Zqiang <qiang1.zhang@...el.com>
AuthorDate:    Fri, 17 Dec 2021 15:42:07 +08:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Sat, 18 Dec 2021 10:55:51 +01:00

locking/rtmutex: Fix incorrect condition in rtmutex_spin_on_owner()

Optimistic spinning needs to be terminated when the spinning waiter is not
longer the top waiter on the lock, but the condition is negated. It
terminates if the waiter is the top waiter, which is defeating the whole
purpose.

Fixes: c3123c431447 ("locking/rtmutex: Dont dereference waiter lockless")
Signed-off-by: Zqiang <qiang1.zhang@...el.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/r/20211217074207.77425-1-qiang1.zhang@intel.com
---
 kernel/locking/rtmutex.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 0c6a48d..1f25a4d 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1380,7 +1380,7 @@ static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
 		 *  - the VCPU on which owner runs is preempted
 		 */
 		if (!owner->on_cpu || need_resched() ||
-		    rt_mutex_waiter_is_top_waiter(lock, waiter) ||
+		    !rt_mutex_waiter_is_top_waiter(lock, waiter) ||
 		    vcpu_is_preempted(task_cpu(owner))) {
 			res = false;
 			break;