[PATCH] sched/deadline: Don't count nr_running twice for dl_server proxy tasks

[PATCH] sched/deadline: Don't count nr_running twice for dl_server proxy tasks

[Yicong Yang]

From: Yicong Yang <yangyicong@hisilicon.com>

On CPU offline the kernel stalled with below call trace:

  INFO: task kworker/0:1:11 blocked for more than 120 seconds.
        Tainted: G           O        6.15.0-rc4+ #1
  "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
  task:kworker/0:1     state:D stack:0     pid:11    tgid:11    ppid:2   task_flags:0x4208060 flags:0x00000008
  Workqueue: events vmstat_shepherd
  Call trace:
   __switch_to+0x118/0x188 (T)
   __schedule+0x31c/0x1300
   schedule+0x3c/0x120
   percpu_rwsem_wait+0x12c/0x1b0
   __percpu_down_read+0x78/0x188
   cpus_read_lock+0xc4/0xe8
   vmstat_shepherd+0x30/0x138
   process_one_work+0x154/0x3c8
   worker_thread+0x2e8/0x400
   kthread+0x154/0x230
   ret_from_fork+0x10/0x20
  INFO: task kworker/1:1:116 blocked for more than 120 seconds.
        Tainted: G           O        6.15.0-rc4+ #1
  "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
  task:kworker/1:1     state:D stack:0     pid:116   tgid:116   ppid:2   task_flags:0x4208060 flags:0x00000008
  Workqueue: events work_for_cpu_fn
  Call trace:
   __switch_to+0x118/0x188 (T)
   __schedule+0x31c/0x1300
   schedule+0x3c/0x120
   schedule_timeout+0x10c/0x120
   __wait_for_common+0xc4/0x1b8
   wait_for_completion+0x28/0x40
   cpuhp_kick_ap_work+0x114/0x3c8
   _cpu_down+0x130/0x4b8
   __cpu_down_maps_locked+0x20/0x38
   work_for_cpu_fn+0x24/0x40
   process_one_work+0x154/0x3c8
   worker_thread+0x2e8/0x400
   kthread+0x154/0x230
   ret_from_fork+0x10/0x20

cpuhp hold the cpu hotplug lock endless and stalled vmstat_shepherd.
This is because we count nr_running twice on cpuhp enqueuing and failed
the wait condition of cpuhp:

enqueue_task_fair() // pick cpuhp from idle, rq->nr_running = 0
  dl_server_start()
    [...]
    add_nr_running() // rq->nr_running = 1
  add_nr_running() // rq->nr_running = 2
[switch to cpuhp, waiting on balance_hotplug_wait()]
rcuwait_wait_event(rq->nr_running == 1 && ...) // failed, rq->nr_running=2
  schedule() // wait again

This doesn't make sense to count one single task twice on
rq->nr_running. So fix this.

Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
---
 kernel/sched/deadline.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index ad45a8fea245..59fb178762ee 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1894,7 +1894,9 @@ void inc_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
 	u64 deadline = dl_se->deadline;
 
 	dl_rq->dl_nr_running++;
-	add_nr_running(rq_of_dl_rq(dl_rq), 1);
+
+	if (!dl_server(dl_se))
+		add_nr_running(rq_of_dl_rq(dl_rq), 1);
 
 	inc_dl_deadline(dl_rq, deadline);
 }
@@ -1904,7 +1906,9 @@ void dec_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
 {
 	WARN_ON(!dl_rq->dl_nr_running);
 	dl_rq->dl_nr_running--;
-	sub_nr_running(rq_of_dl_rq(dl_rq), 1);
+
+	if (!dl_server(dl_se))
+		sub_nr_running(rq_of_dl_rq(dl_rq), 1);
 
 	dec_dl_deadline(dl_rq, dl_se->deadline);
 }
-- 
2.24.0

Re: [PATCH] sched/deadline: Don't count nr_running twice for dl_server proxy tasks

[Juri Lelli]

Hello,

On 27/06/25 11:54, Yicong Yang wrote:
> From: Yicong Yang <yangyicong@hisilicon.com>
> 
> On CPU offline the kernel stalled with below call trace:
> 
>   INFO: task kworker/0:1:11 blocked for more than 120 seconds.
>         Tainted: G           O        6.15.0-rc4+ #1
>   "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>   task:kworker/0:1     state:D stack:0     pid:11    tgid:11    ppid:2   task_flags:0x4208060 flags:0x00000008
>   Workqueue: events vmstat_shepherd
>   Call trace:
>    __switch_to+0x118/0x188 (T)
>    __schedule+0x31c/0x1300
>    schedule+0x3c/0x120
>    percpu_rwsem_wait+0x12c/0x1b0
>    __percpu_down_read+0x78/0x188
>    cpus_read_lock+0xc4/0xe8
>    vmstat_shepherd+0x30/0x138
>    process_one_work+0x154/0x3c8
>    worker_thread+0x2e8/0x400
>    kthread+0x154/0x230
>    ret_from_fork+0x10/0x20
>   INFO: task kworker/1:1:116 blocked for more than 120 seconds.
>         Tainted: G           O        6.15.0-rc4+ #1
>   "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>   task:kworker/1:1     state:D stack:0     pid:116   tgid:116   ppid:2   task_flags:0x4208060 flags:0x00000008
>   Workqueue: events work_for_cpu_fn
>   Call trace:
>    __switch_to+0x118/0x188 (T)
>    __schedule+0x31c/0x1300
>    schedule+0x3c/0x120
>    schedule_timeout+0x10c/0x120
>    __wait_for_common+0xc4/0x1b8
>    wait_for_completion+0x28/0x40
>    cpuhp_kick_ap_work+0x114/0x3c8
>    _cpu_down+0x130/0x4b8
>    __cpu_down_maps_locked+0x20/0x38
>    work_for_cpu_fn+0x24/0x40
>    process_one_work+0x154/0x3c8
>    worker_thread+0x2e8/0x400
>    kthread+0x154/0x230
>    ret_from_fork+0x10/0x20
> 
> cpuhp hold the cpu hotplug lock endless and stalled vmstat_shepherd.
> This is because we count nr_running twice on cpuhp enqueuing and failed
> the wait condition of cpuhp:
> 
> enqueue_task_fair() // pick cpuhp from idle, rq->nr_running = 0
>   dl_server_start()
>     [...]
>     add_nr_running() // rq->nr_running = 1
>   add_nr_running() // rq->nr_running = 2
> [switch to cpuhp, waiting on balance_hotplug_wait()]
> rcuwait_wait_event(rq->nr_running == 1 && ...) // failed, rq->nr_running=2
>   schedule() // wait again
> 
> This doesn't make sense to count one single task twice on
> rq->nr_running. So fix this.
> 
> Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
> ---
>  kernel/sched/deadline.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index ad45a8fea245..59fb178762ee 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1894,7 +1894,9 @@ void inc_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
>  	u64 deadline = dl_se->deadline;
>  
>  	dl_rq->dl_nr_running++;
> -	add_nr_running(rq_of_dl_rq(dl_rq), 1);
> +
> +	if (!dl_server(dl_se))
> +		add_nr_running(rq_of_dl_rq(dl_rq), 1);
>  
>  	inc_dl_deadline(dl_rq, deadline);
>  }
> @@ -1904,7 +1906,9 @@ void dec_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
>  {
>  	WARN_ON(!dl_rq->dl_nr_running);
>  	dl_rq->dl_nr_running--;
> -	sub_nr_running(rq_of_dl_rq(dl_rq), 1);
> +
> +	if (!dl_server(dl_se))
> +		sub_nr_running(rq_of_dl_rq(dl_rq), 1);
>  
>  	dec_dl_deadline(dl_rq, dl_se->deadline);
>  }

This seems to make sense to me. Thanks for the analysis and the patch.

Peter, what do you think?

Thanks,
Juri

Re: [PATCH] sched/deadline: Don't count nr_running twice for dl_server proxy tasks

[Yicong Yang]

Hi Peter,

On 2025/6/27 16:05, Juri Lelli wrote:
> Hello,
> 
> On 27/06/25 11:54, Yicong Yang wrote:
>> From: Yicong Yang <yangyicong@hisilicon.com>
>>
>> On CPU offline the kernel stalled with below call trace:
>>
>>   INFO: task kworker/0:1:11 blocked for more than 120 seconds.
>>         Tainted: G           O        6.15.0-rc4+ #1
>>   "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>>   task:kworker/0:1     state:D stack:0     pid:11    tgid:11    ppid:2   task_flags:0x4208060 flags:0x00000008
>>   Workqueue: events vmstat_shepherd
>>   Call trace:
>>    __switch_to+0x118/0x188 (T)
>>    __schedule+0x31c/0x1300
>>    schedule+0x3c/0x120
>>    percpu_rwsem_wait+0x12c/0x1b0
>>    __percpu_down_read+0x78/0x188
>>    cpus_read_lock+0xc4/0xe8
>>    vmstat_shepherd+0x30/0x138
>>    process_one_work+0x154/0x3c8
>>    worker_thread+0x2e8/0x400
>>    kthread+0x154/0x230
>>    ret_from_fork+0x10/0x20
>>   INFO: task kworker/1:1:116 blocked for more than 120 seconds.
>>         Tainted: G           O        6.15.0-rc4+ #1
>>   "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>>   task:kworker/1:1     state:D stack:0     pid:116   tgid:116   ppid:2   task_flags:0x4208060 flags:0x00000008
>>   Workqueue: events work_for_cpu_fn
>>   Call trace:
>>    __switch_to+0x118/0x188 (T)
>>    __schedule+0x31c/0x1300
>>    schedule+0x3c/0x120
>>    schedule_timeout+0x10c/0x120
>>    __wait_for_common+0xc4/0x1b8
>>    wait_for_completion+0x28/0x40
>>    cpuhp_kick_ap_work+0x114/0x3c8
>>    _cpu_down+0x130/0x4b8
>>    __cpu_down_maps_locked+0x20/0x38
>>    work_for_cpu_fn+0x24/0x40
>>    process_one_work+0x154/0x3c8
>>    worker_thread+0x2e8/0x400
>>    kthread+0x154/0x230
>>    ret_from_fork+0x10/0x20
>>
>> cpuhp hold the cpu hotplug lock endless and stalled vmstat_shepherd.
>> This is because we count nr_running twice on cpuhp enqueuing and failed
>> the wait condition of cpuhp:
>>
>> enqueue_task_fair() // pick cpuhp from idle, rq->nr_running = 0
>>   dl_server_start()
>>     [...]
>>     add_nr_running() // rq->nr_running = 1
>>   add_nr_running() // rq->nr_running = 2
>> [switch to cpuhp, waiting on balance_hotplug_wait()]
>> rcuwait_wait_event(rq->nr_running == 1 && ...) // failed, rq->nr_running=2
>>   schedule() // wait again
>>
>> This doesn't make sense to count one single task twice on
>> rq->nr_running. So fix this.
>>
>> Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
>> ---
>>  kernel/sched/deadline.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>> index ad45a8fea245..59fb178762ee 100644
>> --- a/kernel/sched/deadline.c
>> +++ b/kernel/sched/deadline.c
>> @@ -1894,7 +1894,9 @@ void inc_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
>>  	u64 deadline = dl_se->deadline;
>>  
>>  	dl_rq->dl_nr_running++;
>> -	add_nr_running(rq_of_dl_rq(dl_rq), 1);
>> +
>> +	if (!dl_server(dl_se))
>> +		add_nr_running(rq_of_dl_rq(dl_rq), 1);
>>  
>>  	inc_dl_deadline(dl_rq, deadline);
>>  }
>> @@ -1904,7 +1906,9 @@ void dec_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
>>  {
>>  	WARN_ON(!dl_rq->dl_nr_running);
>>  	dl_rq->dl_nr_running--;
>> -	sub_nr_running(rq_of_dl_rq(dl_rq), 1);
>> +
>> +	if (!dl_server(dl_se))
>> +		sub_nr_running(rq_of_dl_rq(dl_rq), 1);
>>  
>>  	dec_dl_deadline(dl_rq, dl_se->deadline);
>>  }
> 
> This seems to make sense to me. Thanks for the analysis and the patch.
> 
> Peter, what do you think?
> 

does this also make sense to you? or any other solutions you'd like me to try?

thanks.

[tip: sched/urgent] sched/deadline: Don't count nr_running for dl_server proxy tasks

[tip-bot2 for Yicong Yang]

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     52d15521eb75f9b521744db675bee61025d2fa52
Gitweb:        https://git.kernel.org/tip/52d15521eb75f9b521744db675bee61025d2fa52
Author:        Yicong Yang <yangyicong@hisilicon.com>
AuthorDate:    Fri, 27 Jun 2025 11:54:20 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 26 Aug 2025 10:46:01 +02:00

sched/deadline: Don't count nr_running for dl_server proxy tasks

On CPU offline the kernel stalled with below call trace:

  INFO: task kworker/0:1:11 blocked for more than 120 seconds.

cpuhp hold the cpu hotplug lock endless and stalled vmstat_shepherd.
This is because we count nr_running twice on cpuhp enqueuing and failed
the wait condition of cpuhp:

  enqueue_task_fair() // pick cpuhp from idle, rq->nr_running = 0
    dl_server_start()
      [...]
      add_nr_running() // rq->nr_running = 1
    add_nr_running() // rq->nr_running = 2
  [switch to cpuhp, waiting on balance_hotplug_wait()]
  rcuwait_wait_event(rq->nr_running == 1 && ...) // failed, rq->nr_running=2
    schedule() // wait again

It doesn't make sense to count the dl_server towards runnable tasks,
since it runs other tasks.

Fixes: 63ba8422f876 ("sched/deadline: Introduce deadline servers")
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250627035420.37712-1-yangyicong@huawei.com
---
 kernel/sched/deadline.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 88c3bd6..f253012 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1851,7 +1851,9 @@ void inc_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
 	u64 deadline = dl_se->deadline;
 
 	dl_rq->dl_nr_running++;
-	add_nr_running(rq_of_dl_rq(dl_rq), 1);
+
+	if (!dl_server(dl_se))
+		add_nr_running(rq_of_dl_rq(dl_rq), 1);
 
 	inc_dl_deadline(dl_rq, deadline);
 }
@@ -1861,7 +1863,9 @@ void dec_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
 {
 	WARN_ON(!dl_rq->dl_nr_running);
 	dl_rq->dl_nr_running--;
-	sub_nr_running(rq_of_dl_rq(dl_rq), 1);
+
+	if (!dl_server(dl_se))
+		sub_nr_running(rq_of_dl_rq(dl_rq), 1);
 
 	dec_dl_deadline(dl_rq, dl_se->deadline);
 }