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Message-ID: <ed1d5f9ec17a5b8d758c234562dad47cfc872ed8.camel@gmx.de>
Date: Sun, 01 Aug 2021 17:14:49 +0200
From: Mike Galbraith <efault@....de>
To: Thomas Gleixner <tglx@...utronix.de>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
linux-rt-users@...r.kernel.org,
Steven Rostedt <rostedt@...dmis.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: v5.14-rc3-rt1 losing wakeups?
On Sun, 2021-08-01 at 05:36 +0200, Mike Galbraith wrote:
> On Fri, 2021-07-30 at 22:49 +0200, Thomas Gleixner wrote:
> > >
> > > First symptom is KDE/Plasma's task manager going comatose. Notice soon
> >
> > KDE/Plasma points at the new fangled rtmutex based ww_mutex from
> > Peter.
>
> Seems not. When booting KVM box with nomodeset, there's exactly one
> early boot ww_mutex lock/unlock, ancient history at the failure point.
As you've probably already surmised given it isn't the ww_mutex bits,
it's the wake_q bits. Apply the below, 5.14-rt ceases to fail. Take
perfectly healthy 5.13-rt, apply those bits, and it instantly begins
failing as 5.14-rt had been.
---
include/linux/sched/wake_q.h | 7 +------
kernel/futex.c | 4 ++--
kernel/locking/rtmutex.c | 18 +++++++++++-------
kernel/locking/rtmutex_api.c | 6 +++---
kernel/locking/rtmutex_common.h | 22 +++++++++++-----------
kernel/sched/core.c | 4 ++--
6 files changed, 30 insertions(+), 31 deletions(-)
--- a/include/linux/sched/wake_q.h
+++ b/include/linux/sched/wake_q.h
@@ -61,11 +61,6 @@ static inline bool wake_q_empty(struct w
extern void wake_q_add(struct wake_q_head *head, struct task_struct *task);
extern void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task);
-extern void __wake_up_q(struct wake_q_head *head, unsigned int state);
-
-static inline void wake_up_q(struct wake_q_head *head)
-{
- __wake_up_q(head, TASK_NORMAL);
-}
+extern void wake_up_q(struct wake_q_head *head);
#endif /* _LINUX_SCHED_WAKE_Q_H */
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1499,11 +1499,11 @@ static void mark_wake_futex(struct wake_
*/
static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
{
+ DEFINE_RT_MUTEX_WAKE_Q_HEAD(wqh);
+ u32 curval, newval;
struct rt_mutex_waiter *top_waiter;
struct task_struct *new_owner;
bool postunlock = false;
- DEFINE_RT_WAKE_Q(wqh);
- u32 curval, newval;
int ret = 0;
top_waiter = rt_mutex_top_waiter(&pi_state->pi_mutex);
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -425,20 +425,24 @@ static __always_inline void rt_mutex_adj
}
/* RT mutex specific wake_q wrappers */
-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_mutex_wake_q_head *wqh,
struct rt_mutex_waiter *w)
{
if (IS_ENABLED(CONFIG_PREEMPT_RT) && w->wake_state != TASK_NORMAL) {
- wake_q_add(&wqh->rt_head, w->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_mutex_wake_q_head *wqh)
{
- if (IS_ENABLED(CONFIG_PREEMPT_RT) && !wake_q_empty(&wqh->rt_head))
- __wake_up_q(&wqh->rt_head, TASK_RTLOCK_WAIT);
+ 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);
@@ -1111,7 +1115,7 @@ static int __sched task_blocks_on_rt_mut
*
* Called with lock->wait_lock held and interrupts disabled.
*/
-static void __sched mark_wakeup_next_waiter(struct rt_wake_q_head *wqh,
+static void __sched mark_wakeup_next_waiter(struct rt_mutex_wake_q_head *wqh,
struct rt_mutex_base *lock)
{
struct rt_mutex_waiter *waiter;
@@ -1210,7 +1214,7 @@ static __always_inline int __rt_mutex_tr
*/
static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock)
{
- DEFINE_RT_WAKE_Q(wqh);
+ DEFINE_RT_MUTEX_WAKE_Q_HEAD(wqh);
unsigned long flags;
/* irqsave required to support early boot calls */
--- a/kernel/locking/rtmutex_api.c
+++ b/kernel/locking/rtmutex_api.c
@@ -141,7 +141,7 @@ int __sched __rt_mutex_futex_trylock(str
* @wqh: The wake queue head from which to get the next lock waiter
*/
bool __sched __rt_mutex_futex_unlock(struct rt_mutex_base *lock,
- struct rt_wake_q_head *wqh)
+ struct rt_mutex_wake_q_head *wqh)
{
lockdep_assert_held(&lock->wait_lock);
@@ -165,7 +165,7 @@ bool __sched __rt_mutex_futex_unlock(str
void __sched rt_mutex_futex_unlock(struct rt_mutex_base *lock)
{
- DEFINE_RT_WAKE_Q(wqh);
+ DEFINE_RT_MUTEX_WAKE_Q_HEAD(wqh);
unsigned long flags;
bool postunlock;
@@ -454,7 +454,7 @@ void __sched rt_mutex_adjust_pi(struct t
/*
* Performs the wakeup of the top-waiter and re-enables preemption.
*/
-void __sched rt_mutex_postunlock(struct rt_wake_q_head *wqh)
+void __sched rt_mutex_postunlock(struct rt_mutex_wake_q_head *wqh)
{
rt_mutex_wake_up_q(wqh);
}
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -42,20 +42,20 @@ 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
- * @rt_head: The wake_q_head for RT lock (spin/rwlock) variants
+ * rt_mutex_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
+ * @rtlock_task: Task pointer for RT lock (spin/rwlock) wakeups
*/
-struct rt_wake_q_head {
+struct rt_mutex_wake_q_head {
struct wake_q_head head;
- struct wake_q_head rt_head;
+ struct task_struct *rtlock_task;
};
-#define DEFINE_RT_WAKE_Q(name) \
- struct rt_wake_q_head name = { \
+#define DEFINE_RT_MUTEX_WAKE_Q_HEAD(name) \
+ struct rt_mutex_wake_q_head name = { \
.head = WAKE_Q_HEAD_INITIALIZER(name.head), \
- .rt_head = WAKE_Q_HEAD_INITIALIZER(name.rt_head),\
+ .rtlock_task = NULL, \
}
/*
@@ -81,9 +81,9 @@ extern int __rt_mutex_futex_trylock(stru
extern void rt_mutex_futex_unlock(struct rt_mutex_base *lock);
extern bool __rt_mutex_futex_unlock(struct rt_mutex_base *lock,
- struct rt_wake_q_head *wqh);
+ struct rt_mutex_wake_q_head *wqh);
-extern void rt_mutex_postunlock(struct rt_wake_q_head *wqh);
+extern void rt_mutex_postunlock(struct rt_mutex_wake_q_head *wqh);
/*
* Must be guarded because this header is included from rcu/tree_plugin.h
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -920,7 +920,7 @@ void wake_q_add_safe(struct wake_q_head
put_task_struct(task);
}
-void __wake_up_q(struct wake_q_head *head, unsigned int state)
+void wake_up_q(struct wake_q_head *head)
{
struct wake_q_node *node = head->first;
@@ -936,7 +936,7 @@ void __wake_up_q(struct wake_q_head *hea
* wake_up_process() executes a full barrier, which pairs with
* the queueing in wake_q_add() so as not to miss wakeups.
*/
- wake_up_state(task, state);
+ wake_up_process(task);
put_task_struct(task);
}
}
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