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locking/rtmutex: Prepare RT rt_mutex_wake_q for RT locks

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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
This commit is contained in:
Thomas Gleixner 2021-08-15 23:28:11 +02:00 • committed by Ingo Molnar
parent 7980aa397c
commit 456cfbc65c
2 changed files with 20 additions and 3 deletions
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18
kernel/locking/rtmutex.c
View file

@ -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, static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh,
struct rt_mutex_waiter *w) 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) 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() */ /* Pairs with preempt_disable() in mark_wakeup_next_waiter() */
preempt_enable(); preempt_enable();

5
kernel/locking/rtmutex_common.h
View file

@ -42,15 +42,18 @@ struct rt_mutex_waiter {
/** /**
* rt_wake_q_head - Wrapper around regular wake_q_head to support * rt_wake_q_head - Wrapper around regular wake_q_head to support
* "sleeping" spinlocks on RT * "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 rt_wake_q_head {
struct wake_q_head head; struct wake_q_head head;
struct task_struct *rtlock_task;
}; };
#define DEFINE_RT_WAKE_Q(name) \ #define DEFINE_RT_WAKE_Q(name) \
struct rt_wake_q_head name = { \ struct rt_wake_q_head name = { \
.head = WAKE_Q_HEAD_INITIALIZER(name.head), \ .head = WAKE_Q_HEAD_INITIALIZER(name.head), \
.rtlock_task = NULL, \
} }
/* /*