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From 34b399662682e7d121a12d7f11c06f809c60d085 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Sat, 25 Jun 2011 09:21:04 +0200
Subject: [PATCH 074/191] sched: Add saved_state for tasks blocked on sleeping
locks
Spinlocks are state preserving in !RT. RT changes the state when a
task gets blocked on a lock. So we need to remember the state before
the lock contention. If a regular wakeup (not a RTmutex related
wakeup) happens, the saved_state is updated to running. When the lock
sleep is done, the saved state is restored.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/sched.h | 3 +++
kernel/sched/core.c | 34 ++++++++++++++++++++++++++++++++--
kernel/sched/sched.h | 1 +
3 files changed, 36 insertions(+), 2 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index c8998312d7bc..3f05b8c29132 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -655,6 +655,8 @@ struct task_struct {
#endif
/* -1 unrunnable, 0 runnable, >0 stopped: */
volatile long state;
+ /* saved state for "spinlock sleepers" */
+ volatile long saved_state;
/*
* This begins the randomizable portion of task_struct. Only
@@ -1780,6 +1782,7 @@ extern struct task_struct *find_get_task_by_vpid(pid_t nr);
extern int wake_up_state(struct task_struct *tsk, unsigned int state);
extern int wake_up_process(struct task_struct *tsk);
+extern int wake_up_lock_sleeper(struct task_struct *tsk);
extern void wake_up_new_task(struct task_struct *tsk);
#ifdef CONFIG_SMP
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 98191218d891..4efe6fd72719 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3314,7 +3314,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
int cpu, success = 0;
preempt_disable();
- if (p == current) {
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT) && p == current) {
/*
* We're waking current, this means 'p->on_rq' and 'task_cpu(p)
* == smp_processor_id()'. Together this means we can special
@@ -3344,8 +3344,26 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
*/
raw_spin_lock_irqsave(&p->pi_lock, flags);
smp_mb__after_spinlock();
- if (!(p->state & state))
+ if (!(p->state & state)) {
+ /*
+ * The task might be running due to a spinlock sleeper
+ * wakeup. Check the saved state and set it to running
+ * if the wakeup condition is true.
+ */
+ if (!(wake_flags & WF_LOCK_SLEEPER)) {
+ if (p->saved_state & state) {
+ p->saved_state = TASK_RUNNING;
+ success = 1;
+ }
+ }
goto unlock;
+ }
+ /*
+ * If this is a regular wakeup, then we can unconditionally
+ * clear the saved state of a "lock sleeper".
+ */
+ if (!(wake_flags & WF_LOCK_SLEEPER))
+ p->saved_state = TASK_RUNNING;
trace_sched_waking(p);
@@ -3534,6 +3552,18 @@ int wake_up_process(struct task_struct *p)
}
EXPORT_SYMBOL(wake_up_process);
+/**
+ * wake_up_lock_sleeper - Wake up a specific process blocked on a "sleeping lock"
+ * @p: The process to be woken up.
+ *
+ * Same as wake_up_process() above, but wake_flags=WF_LOCK_SLEEPER to indicate
+ * the nature of the wakeup.
+ */
+int wake_up_lock_sleeper(struct task_struct *p)
+{
+ return try_to_wake_up(p, TASK_UNINTERRUPTIBLE, WF_LOCK_SLEEPER);
+}
+
int wake_up_state(struct task_struct *p, unsigned int state)
{
return try_to_wake_up(p, state, 0);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 10a1522b1e30..b65a4e244a77 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1751,6 +1751,7 @@ static inline int task_on_rq_migrating(struct task_struct *p)
#define WF_SYNC 0x10 /* Waker goes to sleep after wakeup */
#define WF_MIGRATED 0x20 /* Internal use, task got migrated */
#define WF_ON_CPU 0x40 /* Wakee is on_cpu */
+#define WF_LOCK_SLEEPER 0x80 /* Wakeup spinlock "sleeper" */
#ifdef CONFIG_SMP
static_assert(WF_EXEC == SD_BALANCE_EXEC);
--
2.19.1
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