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@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211217074207.77425-1-qiang1.zhang@intel.com

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 0c6a48d..1f25a4d 100644 (file)
--- 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;