[GIT PULL] scheduler fixes

Ingo Molnar
2015-02-20T13:42:46Z

Linus,

Please pull the latest sched-urgent-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-for-linus

# HEAD: 2636ed5f8d15ff9395731593537b4b3fdf2af24d sched/rt: Avoid obvious configuration fail

This tree contains misc fixes: preempt_schedule_common()
and io_schedule() recursion fixes, sched/dl fixes, a
completion_done() revert, two sched/rt fixes and a comment
update patch.

Thanks,

Ingo

------------------>
Frederic Weisbecker (1):
sched: Fix preempt_schedule_common() triggering tracing recursion

Kirill Tkhai (2):
sched/dl: Prevent enqueue of a sleeping task in dl_task_timer()
sched/dl: Do update_rq_clock() in yield_task_dl()

NeilBrown (1):
sched: Prevent recursion in io_schedule()

Oleg Nesterov (1):
sched/completion: Serialize completion_done() with complete()

Peter Zijlstra (4):
sched: Clarify ordering between task_rq_lock() and move_queued_task()
sched: Make dl_task_time() use task_rq_lock()
sched/autogroup: Fix failure to set cpu.rt_runtime_us
sched/rt: Avoid obvious configuration fail

include/linux/sched.h | 10 ++--
kernel/sched/auto_group.c | 6 +--
kernel/sched/completion.c | 19 +++++++-
kernel/sched/core.c | 113 ++++++++++++----------------------------------
kernel/sched/deadline.c | 33 ++++++++++----
kernel/sched/sched.h | 76 +++++++++++++++++++++++++++++++
6 files changed, 155 insertions(+), 102 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8db31ef98d2f..cb5cdc777c8a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -363,9 +363,6 @@ extern void show_regs(struct pt_regs *);
*/
extern void show_stack(struct task_struct *task, unsigned long *sp);

-void io_schedule(void);
-long io_schedule_timeout(long timeout);
-
extern void cpu_init (void);
extern void trap_init(void);
extern void update_process_times(int user);
@@ -422,6 +419,13 @@ extern signed long schedule_timeout_uninterruptible(signed long timeout);
asmlinkage void schedule(void);
extern void schedule_preempt_disabled(void);

+extern long io_schedule_timeout(long timeout);
+
+static inline void io_schedule(void)
+{
+ io_schedule_timeout(MAX_SCHEDULE_TIMEOUT);
+}
+
struct nsproxy;
struct user_namespace;

diff --git a/kernel/sched/auto_group.c b/kernel/sched/auto_group.c
index 8a2e230fb86a..eae160dd669d 100644
--- a/kernel/sched/auto_group.c
+++ b/kernel/sched/auto_group.c
@@ -87,8 +87,7 @@ static inline struct autogroup *autogroup_create(void)
* so we don't have to move tasks around upon policy change,
* or flail around trying to allocate bandwidth on the fly.
* A bandwidth exception in __sched_setscheduler() allows
- * the policy change to proceed. Thereafter, task_group()
- * returns &root_task_group, so zero bandwidth is required.
+ * the policy change to proceed.
*/
free_rt_sched_group(tg);
tg->rt_se = root_task_group.rt_se;
@@ -115,9 +114,6 @@ bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
if (tg != &root_task_group)
return false;

- if (p->sched_class != &fair_sched_class)
- return false;
-
/*
* We can only assume the task group can't go away on us if
* autogroup_move_group() can see us on ->thread_group list.
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 7052d3fd4e7b..8d0f35debf35 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -274,7 +274,7 @@ bool try_wait_for_completion(struct completion *x)
* first without taking the lock so we can
* return early in the blocking case.
*/
- if (!ACCESS_ONCE(x->done))
+ if (!READ_ONCE(x->done))
return 0;

spin_lock_irqsave(&x->wait.lock, flags);
@@ -297,6 +297,21 @@ EXPORT_SYMBOL(try_wait_for_completion);
*/
bool completion_done(struct completion *x)
{
- return !!ACCESS_ONCE(x->done);
+ if (!READ_ONCE(x->done))
+ return false;
+
+ /*
+ * If ->done, we need to wait for complete() to release ->wait.lock
+ * otherwise we can end up freeing the completion before complete()
+ * is done referencing it.
+ *
+ * The RMB pairs with complete()'s RELEASE of ->wait.lock and orders
+ * the loads of ->done and ->wait.lock such that we cannot observe
+ * the lock before complete() acquires it while observing the ->done
+ * after it's acquired the lock.
+ */
+ smp_rmb();
+ spin_unlock_wait(&x->wait.lock);
+ return true;
}
EXPORT_SYMBOL(completion_done);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1f37fe7f77a4..a4869bd426ca 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -307,66 +307,6 @@ __read_mostly int scheduler_running;
int sysctl_sched_rt_runtime = 950000;

/*
- * __task_rq_lock - lock the rq @p resides on.
- */
-static inline struct rq *__task_rq_lock(struct task_struct *p)
- __acquires(rq->lock)
-{
- struct rq *rq;
-
- lockdep_assert_held(&p->pi_lock);
-
- for (;;) {
- rq = task_rq(p);
- raw_spin_lock(&rq->lock);
- if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
- return rq;
- raw_spin_unlock(&rq->lock);
-
- while (unlikely(task_on_rq_migrating(p)))
- cpu_relax();
- }
-}
-
-/*
- * task_rq_lock - lock p->pi_lock and lock the rq @p resides on.
- */
-static struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags)
- __acquires(p->pi_lock)
- __acquires(rq->lock)
-{
- struct rq *rq;
-
- for (;;) {
- raw_spin_lock_irqsave(&p->pi_lock, *flags);
- rq = task_rq(p);
- raw_spin_lock(&rq->lock);
- if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
- return rq;
- raw_spin_unlock(&rq->lock);
- raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
-
- while (unlikely(task_on_rq_migrating(p)))
- cpu_relax();
- }
-}
-
-static void __task_rq_unlock(struct rq *rq)
- __releases(rq->lock)
-{
- raw_spin_unlock(&rq->lock);
-}
-
-static inline void
-task_rq_unlock(struct rq *rq, struct task_struct *p, unsigned long *flags)
- __releases(rq->lock)
- __releases(p->pi_lock)
-{
- raw_spin_unlock(&rq->lock);
- raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
-}
-
-/*
* this_rq_lock - lock this runqueue and disable interrupts.
*/
static struct rq *this_rq_lock(void)
@@ -2899,7 +2839,7 @@ void __sched schedule_preempt_disabled(void)
preempt_disable();
}

-static void preempt_schedule_common(void)
+static void __sched notrace preempt_schedule_common(void)
{
do {
__preempt_count_add(PREEMPT_ACTIVE);
@@ -4418,36 +4358,29 @@ EXPORT_SYMBOL_GPL(yield_to);
* This task is about to go to sleep on IO. Increment rq->nr_iowait so
* that process accounting knows that this is a task in IO wait state.
*/
-void __sched io_schedule(void)
-{
- struct rq *rq = raw_rq();
-
- delayacct_blkio_start();
- atomic_inc(&rq->nr_iowait);
- blk_flush_plug(current);
- current->in_iowait = 1;
- schedule();
- current->in_iowait = 0;
- atomic_dec(&rq->nr_iowait);
- delayacct_blkio_end();
-}
-EXPORT_SYMBOL(io_schedule);
-
long __sched io_schedule_timeout(long timeout)
{
- struct rq *rq = raw_rq();
+ int old_iowait = current->in_iowait;
+ struct rq *rq;
long ret;

+ current->in_iowait = 1;
+ if (old_iowait)
+ blk_schedule_flush_plug(current);
+ else
+ blk_flush_plug(current);
+
delayacct_blkio_start();
+ rq = raw_rq();
atomic_inc(&rq->nr_iowait);
- blk_flush_plug(current);
- current->in_iowait = 1;
ret = schedule_timeout(timeout);
- current->in_iowait = 0;
+ current->in_iowait = old_iowait;
atomic_dec(&rq->nr_iowait);
delayacct_blkio_end();
+
return ret;
}
+EXPORT_SYMBOL(io_schedule_timeout);

/**
* sys_sched_get_priority_max - return maximum RT priority.
@@ -7644,6 +7577,12 @@ static inline int tg_has_rt_tasks(struct task_group *tg)
{
struct task_struct *g, *p;

+ /*
+ * Autogroups do not have RT tasks; see autogroup_create().
+ */
+ if (task_group_is_autogroup(tg))
+ return 0;
+
for_each_process_thread(g, p) {
if (rt_task(p) && task_group(p) == tg)
return 1;
@@ -7736,6 +7675,17 @@ static int tg_set_rt_bandwidth(struct task_group *tg,
{
int i, err = 0;

+ /*
+ * Disallowing the root group RT runtime is BAD, it would disallow the
+ * kernel creating (and or operating) RT threads.
+ */
+ if (tg == &root_task_group && rt_runtime == 0)
+ return -EINVAL;
+
+ /* No period doesn't make any sense. */
+ if (rt_period == 0)
+ return -EINVAL;
+
mutex_lock(&rt_constraints_mutex);
read_lock(&tasklist_lock);
err = __rt_schedulable(tg, rt_period, rt_runtime);
@@ -7792,9 +7742,6 @@ static int sched_group_set_rt_period(struct task_group *tg, long rt_period_us)
rt_period = (u64)rt_period_us * NSEC_PER_USEC;
rt_runtime = tg->rt_bandwidth.rt_runtime;

- if (rt_period == 0)
- return -EINVAL;
-
return tg_set_rt_bandwidth(tg, rt_period, rt_runtime);
}

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index a027799ae130..3fa8fa6d9403 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -511,16 +511,10 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
struct sched_dl_entity,
dl_timer);
struct task_struct *p = dl_task_of(dl_se);
+ unsigned long flags;
struct rq *rq;
-again:
- rq = task_rq(p);
- raw_spin_lock(&rq->lock);

- if (rq != task_rq(p)) {
- /* Task was moved, retrying. */
- raw_spin_unlock(&rq->lock);
- goto again;
- }
+ rq = task_rq_lock(current, &flags);

/*
* We need to take care of several possible races here:
@@ -541,6 +535,26 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)

sched_clock_tick();
update_rq_clock(rq);
+
+ /*
+ * If the throttle happened during sched-out; like:
+ *
+ * schedule()
+ * deactivate_task()
+ * dequeue_task_dl()
+ * update_curr_dl()
+ * start_dl_timer()
+ * __dequeue_task_dl()
+ * prev->on_rq = 0;
+ *
+ * We can be both throttled and !queued. Replenish the counter
+ * but do not enqueue -- wait for our wakeup to do that.
+ */
+ if (!task_on_rq_queued(p)) {
+ replenish_dl_entity(dl_se, dl_se);
+ goto unlock;
+ }
+
enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
if (dl_task(rq->curr))
check_preempt_curr_dl(rq, p, 0);
@@ -555,7 +569,7 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
push_dl_task(rq);
#endif
unlock:
- raw_spin_unlock(&rq->lock);
+ task_rq_unlock(rq, current, &flags);

return HRTIMER_NORESTART;
}
@@ -898,6 +912,7 @@ static void yield_task_dl(struct rq *rq)
rq->curr->dl.dl_yielded = 1;
p->dl.runtime = 0;
}
+ update_rq_clock(rq);
update_curr_dl(rq);
}

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0870db23d79c..dc0f435a2779 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1380,6 +1380,82 @@ static inline void sched_avg_update(struct rq *rq) { }

extern void start_bandwidth_timer(struct hrtimer *period_timer, ktime_t period);

+/*
+ * __task_rq_lock - lock the rq @p resides on.
+ */
+static inline struct rq *__task_rq_lock(struct task_struct *p)
+ __acquires(rq->lock)
+{
+ struct rq *rq;
+
+ lockdep_assert_held(&p->pi_lock);
+
+ for (;;) {
+ rq = task_rq(p);
+ raw_spin_lock(&rq->lock);
+ if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
+ return rq;
+ raw_spin_unlock(&rq->lock);
+
+ while (unlikely(task_on_rq_migrating(p)))
+ cpu_relax();
+ }
+}
+
+/*
+ * task_rq_lock - lock p->pi_lock and lock the rq @p resides on.
+ */
+static inline struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags)
+ __acquires(p->pi_lock)
+ __acquires(rq->lock)
+{
+ struct rq *rq;
+
+ for (;;) {
+ raw_spin_lock_irqsave(&p->pi_lock, *flags);
+ rq = task_rq(p);
+ raw_spin_lock(&rq->lock);
+ /*
+ * move_queued_task() task_rq_lock()
+ *
+ * ACQUIRE (rq->lock)
+ * [S] ->on_rq = MIGRATING [L] rq = task_rq()
+ * WMB (__set_task_cpu()) ACQUIRE (rq->lock);
+ * [S] ->cpu = new_cpu [L] task_rq()
+ * [L] ->on_rq
+ * RELEASE (rq->lock)
+ *
+ * If we observe the old cpu in task_rq_lock, the acquire of
+ * the old rq->lock will fully serialize against the stores.
+ *
+ * If we observe the new cpu in task_rq_lock, the acquire will
+ * pair with the WMB to ensure we must then also see migrating.
+ */
+ if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
+ return rq;
+ raw_spin_unlock(&rq->lock);
+ raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
+
+ while (unlikely(task_on_rq_migrating(p)))
+ cpu_relax();
+ }
+}
+
+static inline void __task_rq_unlock(struct rq *rq)
+ __releases(rq->lock)
+{
+ raw_spin_unlock(&rq->lock);
+}
+
+static inline void
+task_rq_unlock(struct rq *rq, struct task_struct *p, unsigned long *flags)
+ __releases(rq->lock)
+ __releases(p->pi_lock)
+{
+ raw_spin_unlock(&rq->lock);
+ raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
+}
+
#ifdef CONFIG_SMP
#ifdef CONFIG_PREEMPT