Li Bin (1):
sched/deadline.c: pick and check task if double_lock_balance() unlock
the rq
Zhou Chengming (1):
sched/rt.c: pick and check task if double_lock_balance() unlock the
rq
kernel/sched/deadline.c | 48 +++++++++++++++++++++++-------------------------
kernel/sched/rt.c | 49 +++++++++++++++++++++++--------------------------
2 files changed, 46 insertions(+), 51 deletions(-)
--
1.7.12.4
From: Zhou Chengming <[email protected]>
push_rt_task() pick the first pushable task and find an eligible
lowest_rq, then double_lock_balance(rq, lowest_rq). So if
double_lock_balance() unlock the rq (when double_lock_balance() return 1),
we have to check if this task is still on the rq.
The problem is that the check conditions are not sufficient:
if (unlikely(task_rq(task) != rq ||
!cpumask_test_cpu(lowest_rq->cpu, &task->cpus_allowed) ||
task_running(rq, task) ||
!rt_task(task) ||
!task_on_rq_queued(task))) {
cpu2 cpu1 cpu0
push_rt_task(rq1)
pick task_A on rq1
find rq0
double_lock_balance(rq1, rq0)
unlock(rq1)
rq1 __schedule
pick task_A run
task_A sleep (dequeued)
lock(rq0)
lock(rq1)
do_above_check(task_A)
task_rq(task_A) == rq1
cpus_allowed unchanged
task_running == false
rt_task(task_A) == true
try_to_wake_up(task_A)
select_cpu = cpu3
enqueue(rq3, task_A)
task_A->on_rq = 1
task_on_rq_queued(task_A)
above_check passed, return rq0
...
migrate task_A from rq1 to rq0
So we can't rely on these checks of task_A to make sure the task_A is
still on the rq1, even though we hold the rq1->lock. This patch will
repick the first pushable task to be sure the task is still on the rq.
Signed-off-by: Zhou Chengming <[email protected]>
Signed-off-by: Li Bin <[email protected]>
---
kernel/sched/rt.c | 49 +++++++++++++++++++++++--------------------------
1 file changed, 23 insertions(+), 26 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index aad49451..e51d574 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1695,6 +1695,26 @@ static int find_lowest_rq(struct task_struct *task)
return -1;
}
+static struct task_struct *pick_next_pushable_task(struct rq *rq)
+{
+ struct task_struct *p;
+
+ if (!has_pushable_tasks(rq))
+ return NULL;
+
+ p = plist_first_entry(&rq->rt.pushable_tasks,
+ struct task_struct, pushable_tasks);
+
+ BUG_ON(rq->cpu != task_cpu(p));
+ BUG_ON(task_current(rq, p));
+ BUG_ON(p->nr_cpus_allowed <= 1);
+
+ BUG_ON(!task_on_rq_queued(p));
+ BUG_ON(!rt_task(p));
+
+ return p;
+}
+
/* Will lock the rq it finds */
static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
{
@@ -1726,13 +1746,10 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
* We had to unlock the run queue. In
* the mean time, task could have
* migrated already or had its affinity changed.
- * Also make sure that it wasn't scheduled on its rq.
*/
- if (unlikely(task_rq(task) != rq ||
- !cpumask_test_cpu(lowest_rq->cpu, &task->cpus_allowed) ||
- task_running(rq, task) ||
- !rt_task(task) ||
- !task_on_rq_queued(task))) {
+ struct task_struct *next_task = pick_next_pushable_task(rq);
+ if (unlikely(next_task != task ||
+ !cpumask_test_cpu(lowest_rq->cpu, &task->cpus_allowed))) {
double_unlock_balance(rq, lowest_rq);
lowest_rq = NULL;
@@ -1752,26 +1769,6 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
return lowest_rq;
}
-static struct task_struct *pick_next_pushable_task(struct rq *rq)
-{
- struct task_struct *p;
-
- if (!has_pushable_tasks(rq))
- return NULL;
-
- p = plist_first_entry(&rq->rt.pushable_tasks,
- struct task_struct, pushable_tasks);
-
- BUG_ON(rq->cpu != task_cpu(p));
- BUG_ON(task_current(rq, p));
- BUG_ON(p->nr_cpus_allowed <= 1);
-
- BUG_ON(!task_on_rq_queued(p));
- BUG_ON(!rt_task(p));
-
- return p;
-}
-
/*
* If the current CPU has more than one RT task, see if the non
* running task can migrate over to a CPU that is running a task
--
1.7.12.4
push_dl_task() pick the first pushable task and find an eligible
later_rq, then double_lock_balance(rq, lowest_rq). So if
double_lock_balance() unlock the rq (when double_lock_balance() return
1), we have to check if this task is still on the rq.
The problem is that the check conditions are not sufficient:
if (unlikely(task_rq(task) != rq ||
!cpumask_test_cpu(later_rq->cpu, &task->cpus_allowed) ||
task_running(rq, task) ||
!dl_task(task) ||
!task_on_rq_queued(task))) {
cpu2 cpu1 cpu0
push_dl_task(rq1)
pick task_A on rq1
find rq0
double_lock_balance(rq1, rq0)
unlock(rq1)
rq1 __schedule
pick task_A run
task_A sleep (dequeued)
lock(rq0)
lock(rq1)
do_above_check(task_A)
task_rq(task_A) == rq1
cpus_allowed unchanged
task_running == false
dl_task(task_A) == true
try_to_wake_up(task_A)
select_cpu = cpu3
enqueue(rq3, task_A)
task_A->on_rq = 1
task_on_rq_queued(task_A)
above_check passed, return rq0
...
migrate task_A from rq1 to rq0
So we can't rely on these checks of task_A to make sure the task_A is
still on the rq1, even though we hold the rq1->lock. This patch will
repick the first pushable task to be sure the task is still on the rq.
Signed-off-by: Li Bin <[email protected]>
---
kernel/sched/deadline.c | 48 +++++++++++++++++++++++-------------------------
1 file changed, 23 insertions(+), 25 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 9df0978..87cd7ca 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1936,6 +1936,26 @@ static int find_later_rq(struct task_struct *task)
return -1;
}
+static struct task_struct *pick_next_pushable_dl_task(struct rq *rq)
+{
+ struct task_struct *p;
+
+ if (!has_pushable_dl_tasks(rq))
+ return NULL;
+
+ p = rb_entry(rq->dl.pushable_dl_tasks_root.rb_leftmost,
+ struct task_struct, pushable_dl_tasks);
+
+ BUG_ON(rq->cpu != task_cpu(p));
+ BUG_ON(task_current(rq, p));
+ BUG_ON(p->nr_cpus_allowed <= 1);
+
+ BUG_ON(!task_on_rq_queued(p));
+ BUG_ON(!dl_task(p));
+
+ return p;
+}
+
/* Locks the rq it finds */
static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq)
{
@@ -1965,11 +1985,9 @@ static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq)
/* Retry if something changed. */
if (double_lock_balance(rq, later_rq)) {
- if (unlikely(task_rq(task) != rq ||
- !cpumask_test_cpu(later_rq->cpu, &task->cpus_allowed) ||
- task_running(rq, task) ||
- !dl_task(task) ||
- !task_on_rq_queued(task))) {
+ struct task_struct *next_task = pick_next_pushable_dl_task(rq);
+ if (unlikely(next_task != task ||
+ !cpumask_test_cpu(later_rq->cpu, &task->cpus_allowed))) {
double_unlock_balance(rq, later_rq);
later_rq = NULL;
break;
@@ -1994,26 +2012,6 @@ static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq)
return later_rq;
}
-static struct task_struct *pick_next_pushable_dl_task(struct rq *rq)
-{
- struct task_struct *p;
-
- if (!has_pushable_dl_tasks(rq))
- return NULL;
-
- p = rb_entry(rq->dl.pushable_dl_tasks_root.rb_leftmost,
- struct task_struct, pushable_dl_tasks);
-
- BUG_ON(rq->cpu != task_cpu(p));
- BUG_ON(task_current(rq, p));
- BUG_ON(p->nr_cpus_allowed <= 1);
-
- BUG_ON(!task_on_rq_queued(p));
- BUG_ON(!dl_task(p));
-
- return p;
-}
-
/*
* See if the non running -deadline tasks on this rq
* can be sent to some other CPU where they can preempt
--
1.7.12.4
On Thu, Apr 12, 2018 at 06:58:53PM +0800, Li Bin wrote:
> Li Bin (1):
> sched/deadline.c: pick and check task if double_lock_balance() unlock
> the rq
>
> Zhou Chengming (1):
> sched/rt.c: pick and check task if double_lock_balance() unlock the
> rq
>
Much thanks!
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Ingo, please apply.
On Thu, 12 Apr 2018 18:58:55 +0800
Li Bin <[email protected]> wrote:
> @@ -1965,11 +1985,9 @@ static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq)
>
> /* Retry if something changed. */
> if (double_lock_balance(rq, later_rq)) {
> - if (unlikely(task_rq(task) != rq ||
> - !cpumask_test_cpu(later_rq->cpu, &task->cpus_allowed) ||
> - task_running(rq, task) ||
> - !dl_task(task) ||
> - !task_on_rq_queued(task))) {
> + struct task_struct *next_task = pick_next_pushable_dl_task(rq);
I would do the same thing here, and add the comment from rt.c as it
is the same reason.
-- Steve
> + if (unlikely(next_task != task ||
> + !cpumask_test_cpu(later_rq->cpu, &task->cpus_allowed))) {
> double_unlock_balance(rq, later_rq);
> later_rq = NULL;
On Thu, 12 Apr 2018 18:58:54 +0800
Li Bin <[email protected]> wrote:
> @@ -1726,13 +1746,10 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
> * We had to unlock the run queue. In
> * the mean time, task could have
> * migrated already or had its affinity changed.
> - * Also make sure that it wasn't scheduled on its rq.
> */
> - if (unlikely(task_rq(task) != rq ||
> - !cpumask_test_cpu(lowest_rq->cpu, &task->cpus_allowed) ||
> - task_running(rq, task) ||
> - !rt_task(task) ||
> - !task_on_rq_queued(task))) {
> + struct task_struct *next_task = pick_next_pushable_task(rq);
Could you declare next_task above the comment. It's better styling.
struct task_struct *next_task;
/*
* Comment
*/
next_task = pick_next_pushable_task(rq);
-- Steve
> + if (unlikely(next_task != task ||
> + !cpumask_test_cpu(lowest_rq->cpu, &task->cpus_allowed))) {
>
> double_unlock_balance(rq, lowest_rq);
> lowest_rq = NULL;
> @@ -1752,26 +1769,6 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
On Thu, 12 Apr 2018 14:11:45 +0200
Peter Zijlstra <[email protected]> wrote:
> On Thu, Apr 12, 2018 at 06:58:53PM +0800, Li Bin wrote:
> > Li Bin (1):
> > sched/deadline.c: pick and check task if double_lock_balance() unlock
> > the rq
> >
> > Zhou Chengming (1):
> > sched/rt.c: pick and check task if double_lock_balance() unlock the
> > rq
> >
>
> Much thanks!
>
> Acked-by: Peter Zijlstra (Intel) <[email protected]>
>
> Ingo, please apply.
You can add my:
Reviewed-by: Steven Rostedt (VMware) <[email protected]>
but I would still like to see the declaration of next_task before the
comment, just for style concerns.
-- Steve
?? 2018/4/12 20:20, Steven Rostedt ะด??:
> On Thu, 12 Apr 2018 14:11:45 +0200
> Peter Zijlstra <[email protected]> wrote:
>
>> On Thu, Apr 12, 2018 at 06:58:53PM +0800, Li Bin wrote:
>>> Li Bin (1):
>>> sched/deadline.c: pick and check task if double_lock_balance() unlock
>>> the rq
>>>
>>> Zhou Chengming (1):
>>> sched/rt.c: pick and check task if double_lock_balance() unlock the
>>> rq
>>>
>>
>> Much thanks!
>>
>> Acked-by: Peter Zijlstra (Intel) <[email protected]>
>>
>> Ingo, please apply.
>
> You can add my:
>
> Reviewed-by: Steven Rostedt (VMware) <[email protected]>
>
> but I would still like to see the declaration of next_task before the
> comment, just for style concerns.
Ok, I will resend the patchset v2.
Thanks,
Li Bin
>
> -- Steve
>
> .
>