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| Started by | Zhou Chengming <zhouchengming1@huawei.com> |
|---|---|
| First post | 2017-09-11 09:00 +0200 |
| Last post | 2017-09-26 05:20 +0200 |
| Articles | 6 — 3 participants |
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[PATCH] sched/rt.c: pick and check task if double_lock_balance() unlock the rq Zhou Chengming <zhouchengming1@huawei.com> - 2017-09-11 09:00 +0200
Re: [PATCH] sched/rt.c: pick and check task if double_lock_balance() unlock the rq zhouchengming <zhouchengming1@huawei.com> - 2017-09-12 04:20 +0200
Re: [PATCH] sched/rt.c: pick and check task if double_lock_balance() unlock the rq zhouchengming <zhouchengming1@huawei.com> - 2017-09-25 14:00 +0200
Re: [PATCH] sched/rt.c: pick and check task if double_lock_balance() unlock the rq Steven Rostedt <rostedt@goodmis.org> - 2017-09-25 21:50 +0200
Re: [PATCH] sched/rt.c: pick and check task if double_lock_balance() unlock the rq zhouchengming <zhouchengming1@huawei.com> - 2017-09-26 03:30 +0200
Re: [PATCH] sched/rt.c: pick and check task if double_lock_balance() unlock the rq Steven Rostedt <rostedt@goodmis.org> - 2017-09-26 05:20 +0200
| From | Zhou Chengming <zhouchengming1@huawei.com> |
|---|---|
| Date | 2017-09-11 09:00 +0200 |
| Subject | [PATCH] sched/rt.c: pick and check task if double_lock_balance() unlock the rq |
| Message-ID | <uoqRk-7DR-17@gated-at.bofh.it> |
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 <zhouchengming1@huawei.com>
---
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 45caf93..787b721 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1703,6 +1703,26 @@ 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)
{
@@ -1734,13 +1754,10 @@ 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;
@@ -1760,26 +1777,6 @@ 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
--
1.8.3.1
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| From | zhouchengming <zhouchengming1@huawei.com> |
|---|---|
| Date | 2017-09-12 04:20 +0200 |
| Subject | Re: [PATCH] sched/rt.c: pick and check task if double_lock_balance() unlock the rq |
| Message-ID | <uoIXT-3tO-5@gated-at.bofh.it> |
| In reply to | #1730177 |
polite ping and +cc, thanks!
On 2017/9/11 14:51, Zhou Chengming wrote:
> 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<zhouchengming1@huawei.com>
> ---
> 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 45caf93..787b721 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1703,6 +1703,26 @@ 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)
> {
> @@ -1734,13 +1754,10 @@ 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;
> @@ -1760,26 +1777,6 @@ 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
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| From | zhouchengming <zhouchengming1@huawei.com> |
|---|---|
| Date | 2017-09-25 14:00 +0200 |
| Subject | Re: [PATCH] sched/rt.c: pick and check task if double_lock_balance() unlock the rq |
| Message-ID | <utAdj-5RX-15@gated-at.bofh.it> |
| In reply to | #1730177 |
ping...
Or it isn't a real problem ?
Thanks.
On 2017/9/11 14:51, Zhou Chengming wrote:
> 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<zhouchengming1@huawei.com>
> ---
> 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 45caf93..787b721 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1703,6 +1703,26 @@ 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)
> {
> @@ -1734,13 +1754,10 @@ 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;
> @@ -1760,26 +1777,6 @@ 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
[toc] | [prev] | [next] | [standalone]
| From | Steven Rostedt <rostedt@goodmis.org> |
|---|---|
| Date | 2017-09-25 21:50 +0200 |
| Subject | Re: [PATCH] sched/rt.c: pick and check task if double_lock_balance() unlock the rq |
| Message-ID | <utHya-2oD-5@gated-at.bofh.it> |
| In reply to | #1730177 |
On Mon, 11 Sep 2017 14:51:49 +0800
Zhou Chengming <zhouchengming1@huawei.com> wrote:
> 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)
How can this happen? The try_to_wake_up(task_A) needs to grab the rq
that task A is on, and we have that rq lock.
/me confused.
-- Steve
> 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 <zhouchengming1@huawei.com>
>
[toc] | [prev] | [next] | [standalone]
| From | zhouchengming <zhouchengming1@huawei.com> |
|---|---|
| Date | 2017-09-26 03:30 +0200 |
| Subject | Re: [PATCH] sched/rt.c: pick and check task if double_lock_balance() unlock the rq |
| Message-ID | <utMRc-65i-3@gated-at.bofh.it> |
| In reply to | #1739247 |
On 2017/9/26 3:40, Steven Rostedt wrote:
> On Mon, 11 Sep 2017 14:51:49 +0800
> Zhou Chengming<zhouchengming1@huawei.com> wrote:
>
>> 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)
> How can this happen? The try_to_wake_up(task_A) needs to grab the rq
> that task A is on, and we have that rq lock.
>
> /me confused.
>
> -- Steve
Thanks for the reply!
After the task_A sleep on cpu1, the try_to_wake_up(task_A) on cpu0 select a different cpu3,
so it will grab the rq3 lock, not the rq1 lock.
Thanks.
>
>> 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<zhouchengming1@huawei.com>
>>
> .
>
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| From | Steven Rostedt <rostedt@goodmis.org> |
|---|---|
| Date | 2017-09-26 05:20 +0200 |
| Subject | Re: [PATCH] sched/rt.c: pick and check task if double_lock_balance() unlock the rq |
| Message-ID | <utOzD-7om-9@gated-at.bofh.it> |
| In reply to | #1739418 |
On Tue, 26 Sep 2017 09:23:20 +0800
zhouchengming <zhouchengming1@huawei.com> wrote:
> On 2017/9/26 3:40, Steven Rostedt wrote:
> > On Mon, 11 Sep 2017 14:51:49 +0800
> > Zhou Chengming<zhouchengming1@huawei.com> wrote:
> >
> >> 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)
> > How can this happen? The try_to_wake_up(task_A) needs to grab the rq
> > that task A is on, and we have that rq lock.
> >
> > /me confused.
> >
> > -- Steve
>
> Thanks for the reply!
> After the task_A sleep on cpu1, the try_to_wake_up(task_A) on cpu0 select a different cpu3,
> so it will grab the rq3 lock, not the rq1 lock.
Ah crap. This is caused by 7608dec2ce20 ("sched: Drop the rq argument
to sched_class::select_task_rq()"). Because this code depends on
try_to_wake_up() grabbing the task's rq lock. But it no longer does
that, and it causes this race.
OK, I need to look at this deeper when I'm not so jetlagged and typing
this because I can't sleep at 5am.
Thanks for pointing this out!
It may be fixed by simply grabbing the run queue lock on migration, as
that would sync things up.
Peter?
-- Steve
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