summaryrefslogtreecommitdiffstats
path: root/kernel/sched/rt.c
diff options
context:
space:
mode:
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/sched/rt.c
parent41d93397334f3c3374810f45e7bcce9007d1a7bb (diff)
downloadop-kernel-dev-ff77e468535987b3d21b7bd4da15608ea3ce7d0b.zip
op-kernel-dev-ff77e468535987b3d21b7bd4da15608ea3ce7d0b.tar.gz
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/sched/rt.c')
-rw-r--r--kernel/sched/rt.c86
1 files changed, 60 insertions, 26 deletions
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 8ec86ab..406a9c2 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);
}
OpenPOWER on IntegriCloud