locking/rtmutex: Prepare RT rt_mutex_wake_q for RT locks

Add an rtlock_task pointer to rt_mutex_wake_q, which allows to handle the RT
specific wakeup for spin/rwlock waiters. The pointer is just consuming 4/8
bytes on the stack so it is provided unconditionaly to avoid #ifdeffery all
over the place.

This cannot use a regular wake_q, because a task can have concurrent wakeups which
would make it miss either lock or the regular wakeups, depending on what gets
queued first, unless task struct gains a separate wake_q_node for this, which
would be overkill, because there can only be a single task which gets woken
up in the spin/rw_lock unlock path.

No functional change for non-RT enabled kernels.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.253614678@linutronix.de

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 5f0d072..8b0d38d 100644 (file)
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -351,12 +351,26 @@ static __always_inline void rt_mutex_adjust_prio(struct task_struct *p)
 static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh,
                                                struct rt_mutex_waiter *w)
 {
-       wake_q_add(&wqh->head, w->task);
+       if (IS_ENABLED(CONFIG_PREEMPT_RT) && w->wake_state != TASK_NORMAL) {
+               if (IS_ENABLED(CONFIG_PROVE_LOCKING))
+                       WARN_ON_ONCE(wqh->rtlock_task);
+               get_task_struct(w->task);
+               wqh->rtlock_task = w->task;
+       } else {
+               wake_q_add(&wqh->head, w->task);
+       }
 }
 
 static __always_inline void rt_mutex_wake_up_q(struct rt_wake_q_head *wqh)
 {
-       wake_up_q(&wqh->head);
+       if (IS_ENABLED(CONFIG_PREEMPT_RT) && wqh->rtlock_task) {
+               wake_up_state(wqh->rtlock_task, TASK_RTLOCK_WAIT);
+               put_task_struct(wqh->rtlock_task);
+               wqh->rtlock_task = NULL;
+       }
+
+       if (!wake_q_empty(&wqh->head))
+               wake_up_q(&wqh->head);
 
        /* Pairs with preempt_disable() in mark_wakeup_next_waiter() */
        preempt_enable();

diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
index ff36316..424ee0f 100644 (file)
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -42,15 +42,18 @@ struct rt_mutex_waiter {
 /**
  * rt_wake_q_head - Wrapper around regular wake_q_head to support
  *                 "sleeping" spinlocks on RT
- * @head:      The regular wake_q_head for sleeping lock variants
+ * @head:              The regular wake_q_head for sleeping lock variants
+ * @rtlock_task:       Task pointer for RT lock (spin/rwlock) wakeups
  */
 struct rt_wake_q_head {
        struct wake_q_head      head;
+       struct task_struct      *rtlock_task;
 };
 
 #define DEFINE_RT_WAKE_Q(name)                                         \
        struct rt_wake_q_head name = {                                  \
                .head           = WAKE_Q_HEAD_INITIALIZER(name.head),   \
+               .rtlock_task    = NULL,                                 \
        }
 
 /*