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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Tue, 6 Oct 2020 13:07:17 +0200
Subject: [PATCH 22/22] locking/rtmutex: Use custom scheduling function for
spin-schedule()
PREEMPT_RT builds the rwsem, mutex, spinlock and rwlock typed locks on
top of a rtmutex lock. While blocked task->pi_blocked_on is set
(tsk_is_pi_blocked()) and task needs to schedule away while waiting.
The schedule process must distinguish between blocking on a regular
sleeping lock (rwsem and mutex) and a RT-only sleeping lock (spinlock
and rwlock):
- rwsem and mutex must flush block requests (blk_schedule_flush_plug())
even if blocked on a lock. This can not deadlock because this also
happens for non-RT.
There should be a warning if the scheduling point is within a RCU read
section.
- spinlock and rwlock must not flush block requests. This will deadlock
if the callback attempts to acquire a lock which is already acquired.
Similarly to being preempted, there should be no warning if the
scheduling point is within a RCU read section.
Add preempt_schedule_lock() which is invoked if scheduling is required
while blocking on a PREEMPT_RT-only sleeping lock.
Remove tsk_is_pi_blocked() from the scheduler path which is no longer
needed with the additional scheduler entry point.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
arch/arm64/include/asm/preempt.h | 3 +++
arch/x86/include/asm/preempt.h | 3 +++
include/asm-generic/preempt.h | 3 +++
include/linux/sched/rt.h | 8 --------
kernel/locking/rtmutex.c | 2 +-
kernel/locking/rwlock-rt.c | 2 +-
kernel/sched/core.c | 32 +++++++++++++++++++++-----------
7 files changed, 32 insertions(+), 21 deletions(-)
--- a/arch/arm64/include/asm/preempt.h
+++ b/arch/arm64/include/asm/preempt.h
@@ -81,6 +81,9 @@ static inline bool should_resched(int pr
#ifdef CONFIG_PREEMPTION
void preempt_schedule(void);
+#ifdef CONFIG_PREEMPT_RT
+void preempt_schedule_lock(void);
+#endif
#define __preempt_schedule() preempt_schedule()
void preempt_schedule_notrace(void);
#define __preempt_schedule_notrace() preempt_schedule_notrace()
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -104,6 +104,9 @@ static __always_inline bool should_resch
}
#ifdef CONFIG_PREEMPTION
+#ifdef CONFIG_PREEMPT_RT
+ extern void preempt_schedule_lock(void);
+#endif
extern asmlinkage void preempt_schedule(void);
extern asmlinkage void preempt_schedule_thunk(void);
--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -79,6 +79,9 @@ static __always_inline bool should_resch
}
#ifdef CONFIG_PREEMPTION
+#ifdef CONFIG_PREEMPT_RT
+extern void preempt_schedule_lock(void);
+#endif
extern asmlinkage void preempt_schedule(void);
#define __preempt_schedule() preempt_schedule()
extern asmlinkage void preempt_schedule_notrace(void);
--- a/include/linux/sched/rt.h
+++ b/include/linux/sched/rt.h
@@ -39,20 +39,12 @@ static inline struct task_struct *rt_mut
}
extern void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task);
extern void rt_mutex_adjust_pi(struct task_struct *p);
-static inline bool tsk_is_pi_blocked(struct task_struct *tsk)
-{
- return tsk->pi_blocked_on != NULL;
-}
#else
static inline struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
{
return NULL;
}
# define rt_mutex_adjust_pi(p) do { } while (0)
-static inline bool tsk_is_pi_blocked(struct task_struct *tsk)
-{
- return false;
-}
#endif
extern void normalize_rt_tasks(void);
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1049,7 +1049,7 @@ void __sched rt_spin_lock_slowlock_locke
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
if (top_waiter != waiter || adaptive_wait(lock, lock_owner))
- schedule();
+ preempt_schedule_lock();
raw_spin_lock_irqsave(&lock->wait_lock, flags);
--- a/kernel/locking/rwlock-rt.c
+++ b/kernel/locking/rwlock-rt.c
@@ -211,7 +211,7 @@ static void __write_rt_lock(struct rt_rw
raw_spin_unlock_irqrestore(&m->wait_lock, flags);
if (atomic_read(&lock->readers) != 0)
- schedule();
+ preempt_schedule_lock();
raw_spin_lock_irqsave(&m->wait_lock, flags);
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5004,7 +5004,7 @@ pick_next_task(struct rq *rq, struct tas
*
* WARNING: must be called with preemption disabled!
*/
-static void __sched notrace __schedule(bool preempt)
+static void __sched notrace __schedule(bool preempt, bool spinning_lock)
{
struct task_struct *prev, *next;
unsigned long *switch_count;
@@ -5057,7 +5057,7 @@ static void __sched notrace __schedule(b
* - ptrace_{,un}freeze_traced() can change ->state underneath us.
*/
prev_state = prev->state;
- if (!preempt && prev_state) {
+ if ((!preempt || spinning_lock) && prev_state) {
if (signal_pending_state(prev_state, prev)) {
prev->state = TASK_RUNNING;
} else {
@@ -5141,7 +5141,7 @@ void __noreturn do_task_dead(void)
/* Tell freezer to ignore us: */
current->flags |= PF_NOFREEZE;
- __schedule(false);
+ __schedule(false, false);
BUG();
/* Avoid "noreturn function does return" - but don't continue if BUG() is a NOP: */
@@ -5174,9 +5174,6 @@ static inline void sched_submit_work(str
preempt_enable_no_resched();
}
- if (tsk_is_pi_blocked(tsk))
- return;
-
/*
* If we are going to sleep and we have plugged IO queued,
* make sure to submit it to avoid deadlocks.
@@ -5202,7 +5199,7 @@ asmlinkage __visible void __sched schedu
sched_submit_work(tsk);
do {
preempt_disable();
- __schedule(false);
+ __schedule(false, false);
sched_preempt_enable_no_resched();
} while (need_resched());
sched_update_worker(tsk);
@@ -5230,7 +5227,7 @@ void __sched schedule_idle(void)
*/
WARN_ON_ONCE(current->state);
do {
- __schedule(false);
+ __schedule(false, false);
} while (need_resched());
}
@@ -5283,7 +5280,7 @@ static void __sched notrace preempt_sche
*/
preempt_disable_notrace();
preempt_latency_start(1);
- __schedule(true);
+ __schedule(true, false);
preempt_latency_stop(1);
preempt_enable_no_resched_notrace();
@@ -5313,6 +5310,19 @@ asmlinkage __visible void __sched notrac
NOKPROBE_SYMBOL(preempt_schedule);
EXPORT_SYMBOL(preempt_schedule);
+#ifdef CONFIG_PREEMPT_RT
+void __sched notrace preempt_schedule_lock(void)
+{
+ do {
+ preempt_disable();
+ __schedule(true, true);
+ sched_preempt_enable_no_resched();
+ } while (need_resched());
+}
+NOKPROBE_SYMBOL(preempt_schedule_lock);
+EXPORT_SYMBOL(preempt_schedule_lock);
+#endif
+
#ifdef CONFIG_PREEMPT_DYNAMIC
DEFINE_STATIC_CALL(preempt_schedule, __preempt_schedule_func);
EXPORT_STATIC_CALL_TRAMP(preempt_schedule);
@@ -5362,7 +5372,7 @@ asmlinkage __visible void __sched notrac
* an infinite recursion.
*/
prev_ctx = exception_enter();
- __schedule(true);
+ __schedule(true, false);
exception_exit(prev_ctx);
preempt_latency_stop(1);
@@ -5580,7 +5590,7 @@ asmlinkage __visible void __sched preemp
do {
preempt_disable();
local_irq_enable();
- __schedule(true);
+ __schedule(true, false);
local_irq_disable();
sched_preempt_enable_no_resched();
} while (need_resched());
|
