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authorPeter Zijlstra <peterz@infradead.org>2016-01-18 15:27:07 +0100
committerIngo Molnar <mingo@kernel.org>2016-02-29 09:53:05 +0100
commitff77e468535987b3d21b7bd4da15608ea3ce7d0b (patch)
treed35cdc7929da435ababea451f8f7e81e76fc76b0 /kernel
parent41d93397334f3c3374810f45e7bcce9007d1a7bb (diff)
sched/rt: Fix PI handling vs. sched_setscheduler()
Andrea Parri reported: > I found that the following scenario (with CONFIG_RT_GROUP_SCHED=y) is not > handled correctly: > > T1 (prio = 20) > lock(rtmutex); > > T2 (prio = 20) > blocks on rtmutex (rt_nr_boosted = 0 on T1's rq) > > T1 (prio = 20) > sys_set_scheduler(prio = 0) > [new_effective_prio == oldprio] > T1 prio = 20 (rt_nr_boosted = 0 on T1's rq) > > The last step is incorrect as T1 is now boosted (c.f., rt_se_boosted()); > in particular, if we continue with > > T1 (prio = 20) > unlock(rtmutex) > wakeup(T2) > adjust_prio(T1) > [prio != rt_mutex_getprio(T1)] > dequeue(T1) > rt_nr_boosted = (unsigned long)(-1) > ... > T1 prio = 0 > > then we end up leaving rt_nr_boosted in an "inconsistent" state. > > The simple program attached could reproduce the previous scenario; note > that, as a consequence of the presence of this state, the "assertion" > > WARN_ON(!rt_nr_running && rt_nr_boosted) > > from dec_rt_group() may trigger. So normally we dequeue/enqueue tasks in sched_setscheduler(), which would ensure the accounting stays correct. However in the early PI path we fail to do so. So this was introduced at around v3.14, by: c365c292d059 ("sched: Consider pi boosting in setscheduler()") which fixed another problem exactly because that dequeue/enqueue, joy. Fix this by teaching rt about DEQUEUE_SAVE/ENQUEUE_RESTORE and have it preserve runqueue location with that option. This requires decoupling the on_rt_rq() state from being on the list. In order to allow for explicit movement during the SAVE/RESTORE, introduce {DE,EN}QUEUE_MOVE. We still must use SAVE/RESTORE in these cases to preserve other invariants. Respecting the SAVE/RESTORE flags also has the (nice) side-effect that things like sys_nice()/sys_sched_setaffinity() also do not reorder FIFO tasks (whereas they used to before this patch). Reported-by: Andrea Parri <parri.andrea@gmail.com> Tested-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Juri Lelli <juri.lelli@arm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/core.c39
-rw-r--r--kernel/sched/rt.c86
-rw-r--r--kernel/sched/sched.h36
3 files changed, 111 insertions, 50 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 291552b4d8ee..bb565b4663c8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2221,6 +2221,10 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
__dl_clear_params(p);
INIT_LIST_HEAD(&p->rt.run_list);
+ p->rt.timeout = 0;
+ p->rt.time_slice = sched_rr_timeslice;
+ p->rt.on_rq = 0;
+ p->rt.on_list = 0;
#ifdef CONFIG_PREEMPT_NOTIFIERS
INIT_HLIST_HEAD(&p->preempt_notifiers);
@@ -3531,7 +3535,7 @@ EXPORT_SYMBOL(default_wake_function);
*/
void rt_mutex_setprio(struct task_struct *p, int prio)
{
- int oldprio, queued, running, enqueue_flag = ENQUEUE_RESTORE;
+ int oldprio, queued, running, queue_flag = DEQUEUE_SAVE | DEQUEUE_MOVE;
struct rq *rq;
const struct sched_class *prev_class;
@@ -3559,11 +3563,15 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
trace_sched_pi_setprio(p, prio);
oldprio = p->prio;
+
+ if (oldprio == prio)
+ queue_flag &= ~DEQUEUE_MOVE;
+
prev_class = p->sched_class;
queued = task_on_rq_queued(p);
running = task_current(rq, p);
if (queued)
- dequeue_task(rq, p, DEQUEUE_SAVE);
+ dequeue_task(rq, p, queue_flag);
if (running)
put_prev_task(rq, p);
@@ -3581,7 +3589,7 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
if (!dl_prio(p->normal_prio) ||
(pi_task && dl_entity_preempt(&pi_task->dl, &p->dl))) {
p->dl.dl_boosted = 1;
- enqueue_flag |= ENQUEUE_REPLENISH;
+ queue_flag |= ENQUEUE_REPLENISH;
} else
p->dl.dl_boosted = 0;
p->sched_class = &dl_sched_class;
@@ -3589,7 +3597,7 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
if (dl_prio(oldprio))
p->dl.dl_boosted = 0;
if (oldprio < prio)
- enqueue_flag |= ENQUEUE_HEAD;
+ queue_flag |= ENQUEUE_HEAD;
p->sched_class = &rt_sched_class;
} else {
if (dl_prio(oldprio))
@@ -3604,7 +3612,7 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
if (running)
p->sched_class->set_curr_task(rq);
if (queued)
- enqueue_task(rq, p, enqueue_flag);
+ enqueue_task(rq, p, queue_flag);
check_class_changed(rq, p, prev_class, oldprio);
out_unlock:
@@ -3960,6 +3968,7 @@ static int __sched_setscheduler(struct task_struct *p,
const struct sched_class *prev_class;
struct rq *rq;
int reset_on_fork;
+ int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE;
/* may grab non-irq protected spin_locks */
BUG_ON(in_interrupt());
@@ -4142,17 +4151,14 @@ change:
* itself.
*/
new_effective_prio = rt_mutex_get_effective_prio(p, newprio);
- if (new_effective_prio == oldprio) {
- __setscheduler_params(p, attr);
- task_rq_unlock(rq, p, &flags);
- return 0;
- }
+ if (new_effective_prio == oldprio)
+ queue_flags &= ~DEQUEUE_MOVE;
}
queued = task_on_rq_queued(p);
running = task_current(rq, p);
if (queued)
- dequeue_task(rq, p, DEQUEUE_SAVE);
+ dequeue_task(rq, p, queue_flags);
if (running)
put_prev_task(rq, p);
@@ -4162,15 +4168,14 @@ change:
if (running)
p->sched_class->set_curr_task(rq);
if (queued) {
- int enqueue_flags = ENQUEUE_RESTORE;
/*
* We enqueue to tail when the priority of a task is
* increased (user space view).
*/
- if (oldprio <= p->prio)
- enqueue_flags |= ENQUEUE_HEAD;
+ if (oldprio < p->prio)
+ queue_flags |= ENQUEUE_HEAD;
- enqueue_task(rq, p, enqueue_flags);
+ enqueue_task(rq, p, queue_flags);
}
check_class_changed(rq, p, prev_class, oldprio);
@@ -7958,7 +7963,7 @@ void sched_move_task(struct task_struct *tsk)
queued = task_on_rq_queued(tsk);
if (queued)
- dequeue_task(rq, tsk, DEQUEUE_SAVE);
+ dequeue_task(rq, tsk, DEQUEUE_SAVE | DEQUEUE_MOVE);
if (unlikely(running))
put_prev_task(rq, tsk);
@@ -7982,7 +7987,7 @@ void sched_move_task(struct task_struct *tsk)
if (unlikely(running))
tsk->sched_class->set_curr_task(rq);
if (queued)
- enqueue_task(rq, tsk, ENQUEUE_RESTORE);
+ enqueue_task(rq, tsk, ENQUEUE_RESTORE | ENQUEUE_MOVE);
task_rq_unlock(rq, tsk, &flags);
}
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 8ec86abe0ea1..406a9c20b210 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -436,7 +436,7 @@ static void dequeue_top_rt_rq(struct rt_rq *rt_rq);
static inline int on_rt_rq(struct sched_rt_entity *rt_se)
{
- return !list_empty(&rt_se->run_list);
+ return rt_se->on_rq;
}
#ifdef CONFIG_RT_GROUP_SCHED
@@ -482,8 +482,8 @@ static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
return rt_se->my_q;
}
-static void enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head);
-static void dequeue_rt_entity(struct sched_rt_entity *rt_se);
+static void enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags);
+static void dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags);
static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
{
@@ -499,7 +499,7 @@ static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
if (!rt_se)
enqueue_top_rt_rq(rt_rq);
else if (!on_rt_rq(rt_se))
- enqueue_rt_entity(rt_se, false);
+ enqueue_rt_entity(rt_se, 0);
if (rt_rq->highest_prio.curr < curr->prio)
resched_curr(rq);
@@ -516,7 +516,7 @@ static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
if (!rt_se)
dequeue_top_rt_rq(rt_rq);
else if (on_rt_rq(rt_se))
- dequeue_rt_entity(rt_se);
+ dequeue_rt_entity(rt_se, 0);
}
static inline int rt_rq_throttled(struct rt_rq *rt_rq)
@@ -1166,7 +1166,30 @@ void dec_rt_tasks(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
dec_rt_group(rt_se, rt_rq);
}
-static void __enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head)
+/*
+ * Change rt_se->run_list location unless SAVE && !MOVE
+ *
+ * assumes ENQUEUE/DEQUEUE flags match
+ */
+static inline bool move_entity(unsigned int flags)
+{
+ if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) == DEQUEUE_SAVE)
+ return false;
+
+ return true;
+}
+
+static void __delist_rt_entity(struct sched_rt_entity *rt_se, struct rt_prio_array *array)
+{
+ list_del_init(&rt_se->run_list);
+
+ if (list_empty(array->queue + rt_se_prio(rt_se)))
+ __clear_bit(rt_se_prio(rt_se), array->bitmap);
+
+ rt_se->on_list = 0;
+}
+
+static void __enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
{
struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
struct rt_prio_array *array = &rt_rq->active;
@@ -1179,26 +1202,37 @@ static void __enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head)
* get throttled and the current group doesn't have any other
* active members.
*/
- if (group_rq && (rt_rq_throttled(group_rq) || !group_rq->rt_nr_running))
+ if (group_rq && (rt_rq_throttled(group_rq) || !group_rq->rt_nr_running)) {
+ if (rt_se->on_list)
+ __delist_rt_entity(rt_se, array);
return;
+ }
- if (head)
- list_add(&rt_se->run_list, queue);
- else
- list_add_tail(&rt_se->run_list, queue);
- __set_bit(rt_se_prio(rt_se), array->bitmap);
+ if (move_entity(flags)) {
+ WARN_ON_ONCE(rt_se->on_list);
+ if (flags & ENQUEUE_HEAD)
+ list_add(&rt_se->run_list, queue);
+ else
+ list_add_tail(&rt_se->run_list, queue);
+
+ __set_bit(rt_se_prio(rt_se), array->bitmap);
+ rt_se->on_list = 1;
+ }
+ rt_se->on_rq = 1;
inc_rt_tasks(rt_se, rt_rq);
}
-static void __dequeue_rt_entity(struct sched_rt_entity *rt_se)
+static void __dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
{
struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
struct rt_prio_array *array = &rt_rq->active;
- list_del_init(&rt_se->run_list);
- if (list_empty(array->queue + rt_se_prio(rt_se)))
- __clear_bit(rt_se_prio(rt_se), array->bitmap);
+ if (move_entity(flags)) {
+ WARN_ON_ONCE(!rt_se->on_list);
+ __delist_rt_entity(rt_se, array);
+ }
+ rt_se->on_rq = 0;
dec_rt_tasks(rt_se, rt_rq);
}
@@ -1207,7 +1241,7 @@ static void __dequeue_rt_entity(struct sched_rt_entity *rt_se)
* Because the prio of an upper entry depends on the lower
* entries, we must remove entries top - down.
*/
-static void dequeue_rt_stack(struct sched_rt_entity *rt_se)
+static void dequeue_rt_stack(struct sched_rt_entity *rt_se, unsigned int flags)
{
struct sched_rt_entity *back = NULL;
@@ -1220,31 +1254,31 @@ static void dequeue_rt_stack(struct sched_rt_entity *rt_se)
for (rt_se = back; rt_se; rt_se = rt_se->back) {
if (on_rt_rq(rt_se))
- __dequeue_rt_entity(rt_se);
+ __dequeue_rt_entity(rt_se, flags);
}
}
-static void enqueue_rt_entity(struct sched_rt_entity *rt_se, bool head)
+static void enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
{
struct rq *rq = rq_of_rt_se(rt_se);
- dequeue_rt_stack(rt_se);
+ dequeue_rt_stack(rt_se, flags);
for_each_sched_rt_entity(rt_se)
- __enqueue_rt_entity(rt_se, head);
+ __enqueue_rt_entity(rt_se, flags);
enqueue_top_rt_rq(&rq->rt);
}
-static void dequeue_rt_entity(struct sched_rt_entity *rt_se)
+static void dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)
{
struct rq *rq = rq_of_rt_se(rt_se);
- dequeue_rt_stack(rt_se);
+ dequeue_rt_stack(rt_se, flags);
for_each_sched_rt_entity(rt_se) {
struct rt_rq *rt_rq = group_rt_rq(rt_se);
if (rt_rq && rt_rq->rt_nr_running)
- __enqueue_rt_entity(rt_se, false);
+ __enqueue_rt_entity(rt_se, flags);
}
enqueue_top_rt_rq(&rq->rt);
}
@@ -1260,7 +1294,7 @@ enqueue_task_rt(struct rq *rq, struct task_struct *p, int flags)
if (flags & ENQUEUE_WAKEUP)
rt_se->timeout = 0;
- enqueue_rt_entity(rt_se, flags & ENQUEUE_HEAD);
+ enqueue_rt_entity(rt_se, flags);
if (!task_current(rq, p) && p->nr_cpus_allowed > 1)
enqueue_pushable_task(rq, p);
@@ -1271,7 +1305,7 @@ static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
struct sched_rt_entity *rt_se = &p->rt;
update_curr_rt(rq);
- dequeue_rt_entity(rt_se);
+ dequeue_rt_entity(rt_se, flags);
dequeue_pushable_task(rq, p);
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 3dc7b8b3f94c..d3606e40ea0d 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1130,18 +1130,40 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
extern const int sched_prio_to_weight[40];
extern const u32 sched_prio_to_wmult[40];
+/*
+ * {de,en}queue flags:
+ *
+ * DEQUEUE_SLEEP - task is no longer runnable
+ * ENQUEUE_WAKEUP - task just became runnable
+ *
+ * SAVE/RESTORE - an otherwise spurious dequeue/enqueue, done to ensure tasks
+ * are in a known state which allows modification. Such pairs
+ * should preserve as much state as possible.
+ *
+ * MOVE - paired with SAVE/RESTORE, explicitly does not preserve the location
+ * in the runqueue.
+ *
+ * ENQUEUE_HEAD - place at front of runqueue (tail if not specified)
+ * ENQUEUE_REPLENISH - CBS (replenish runtime and postpone deadline)
+ * ENQUEUE_WAKING - sched_class::task_waking was called
+ *
+ */
+
+#define DEQUEUE_SLEEP 0x01
+#define DEQUEUE_SAVE 0x02 /* matches ENQUEUE_RESTORE */
+#define DEQUEUE_MOVE 0x04 /* matches ENQUEUE_MOVE */
+
#define ENQUEUE_WAKEUP 0x01
-#define ENQUEUE_HEAD 0x02
+#define ENQUEUE_RESTORE 0x02
+#define ENQUEUE_MOVE 0x04
+
+#define ENQUEUE_HEAD 0x08
+#define ENQUEUE_REPLENISH 0x10
#ifdef CONFIG_SMP
-#define ENQUEUE_WAKING 0x04 /* sched_class::task_waking was called */
+#define ENQUEUE_WAKING 0x20
#else
#define ENQUEUE_WAKING 0x00
#endif
-#define ENQUEUE_REPLENISH 0x08
-#define ENQUEUE_RESTORE 0x10
-
-#define DEQUEUE_SLEEP 0x01
-#define DEQUEUE_SAVE 0x02
#define RETRY_TASK ((void *)-1UL)