The WARN_DOUBLE_CLOCK warning is triggered during cpu offline.
------------[ cut here ]------------
rq->clock_update_flags & RQCF_UPDATED
WARNING: CPU: 17 PID: 138 at kernel/sched/core.c:741
update_rq_clock+0xaf/0x180
Call Trace:
<TASK>
__balance_push_cpu_stop+0x146/0x180
? migration_cpu_stop+0x2a0/0x2a0
cpu_stopper_thread+0xa3/0x140
smpboot_thread_fn+0x14f/0x210
? sort_range+0x20/0x20
kthread+0xe6/0x110
? kthread_complete_and_exit+0x20/0x20
ret_from_fork+0x1f/0x30
To avoid this warning, we remove update_rq_clock() from
the __migrate_task() function. And in order to avoid
missing rq clock update, add update_rq_clock() call before
migration_cpu_stop() calls __migrate_task().
Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
---
kernel/sched/core.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a8be5415daba..1eca36299d8b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2398,7 +2398,6 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
if (!is_cpu_allowed(p, dest_cpu))
return rq;
- update_rq_clock(rq);
rq = move_queued_task(rq, rf, p, dest_cpu);
return rq;
@@ -2456,10 +2455,12 @@ static int migration_cpu_stop(void *data)
goto out;
}
- if (task_on_rq_queued(p))
+ if (task_on_rq_queued(p)) {
+ update_rq_clock(rq);
rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
- else
+ } else {
p->wake_cpu = arg->dest_cpu;
+ }
/*
* XXX __migrate_task() can fail, at which point we might end
--
2.20.1On Tue, Jun 13, 2023 at 04:20:10PM +0800, Hao Jia wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a8be5415daba..1eca36299d8b 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2398,7 +2398,6 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
> if (!is_cpu_allowed(p, dest_cpu))
> return rq;
>
> - update_rq_clock(rq);
> rq = move_queued_task(rq, rf, p, dest_cpu);
>
> return rq;
> @@ -2456,10 +2455,12 @@ static int migration_cpu_stop(void *data)
> goto out;
> }
>
> - if (task_on_rq_queued(p))
> + if (task_on_rq_queued(p)) {
> + update_rq_clock(rq);
> rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
> - else
> + } else {
> p->wake_cpu = arg->dest_cpu;
> + }
>
> /*
> * XXX __migrate_task() can fail, at which point we might end
So now you've got update_rq_clock() in both callers, why not remove it
from __balance_push_cpu_stop() ?
Afaict nothing actually needs it before __migrate_task().
---
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9435,8 +9435,6 @@ static int __balance_push_cpu_stop(void
raw_spin_lock_irq(&p->pi_lock);
rq_lock(rq, &rf);
- update_rq_clock(rq);
-
if (task_rq(p) == rq && task_on_rq_queued(p)) {
cpu = select_fallback_rq(rq->cpu, p);
rq = __migrate_task(rq, &rf, p, cpu);
On 2023/6/15 Peter Zijlstra wrote:
> On Tue, Jun 13, 2023 at 04:20:10PM +0800, Hao Jia wrote:
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index a8be5415daba..1eca36299d8b 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -2398,7 +2398,6 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
>> if (!is_cpu_allowed(p, dest_cpu))
>> return rq;
>>
>> - update_rq_clock(rq);
>> rq = move_queued_task(rq, rf, p, dest_cpu);
>>
>> return rq;
>> @@ -2456,10 +2455,12 @@ static int migration_cpu_stop(void *data)
>> goto out;
>> }
>>
>> - if (task_on_rq_queued(p))
>> + if (task_on_rq_queued(p)) {
>> + update_rq_clock(rq);
>> rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
>> - else
>> + } else {
>> p->wake_cpu = arg->dest_cpu;
>> + }
>>
>> /*
>> * XXX __migrate_task() can fail, at which point we might end
>
> So now you've got update_rq_clock() in both callers, why not remove it
> from __balance_push_cpu_stop() ?
>
> Afaict nothing actually needs it before __migrate_task().
>
Thanks for your review.
I'm afraid not, the rq clock also needs to be updated before
select_fallback_rq() is called.
> ---
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -9435,8 +9435,6 @@ static int __balance_push_cpu_stop(void
> raw_spin_lock_irq(&p->pi_lock);
> rq_lock(rq, &rf);
>
> - update_rq_clock(rq);
> -
> if (task_rq(p) == rq && task_on_rq_queued(p)) {
> cpu = select_fallback_rq(rq->cpu, p);
> rq = __migrate_task(rq, &rf, p, cpu);
If we just remove update_rq_clock() from __balance_push_cpu_stop(), we
will get this warning.
[ 1260.960166] rq->clock_update_flags < RQCF_ACT_SKIP
[ 1260.960170] WARNING: CPU: 25 PID: 196 at kernel/sched/sched.h:1496
update_curr+0xf6/0x1f0
[ 1260.960318] Call Trace:
[ 1260.960320] <TASK>
[ 1260.960323] ? show_regs+0x5b/0x60
[ 1260.960327] ? __warn+0x89/0x140
[ 1260.960331] ? update_curr+0xf6/0x1f0
[ 1260.960334] ? report_bug+0x1b7/0x1e0
[ 1260.960338] ? __wake_up_klogd.part.25+0x5a/0x80
[ 1260.960342] ? handle_bug+0x45/0x80
[ 1260.960346] ? exc_invalid_op+0x18/0x70
[ 1260.960348] ? asm_exc_invalid_op+0x1b/0x20
[ 1260.960354] ? update_curr+0xf6/0x1f0
[ 1260.960356] ? update_curr+0xf6/0x1f0
[ 1260.960359] dequeue_entity+0x3b/0x410
[ 1260.960361] dequeue_task_fair+0xc7/0x3c0
[ 1260.960363] dequeue_task+0x30/0xf0
[ 1260.960365] __do_set_cpus_allowed+0x94/0x130
[ 1260.960366] do_set_cpus_allowed+0x38/0x60
[ 1260.960368] cpuset_cpus_allowed_fallback+0x70/0x80
[ 1260.960372] select_fallback_rq+0x20f/0x250 <----
[ 1260.960374] __balance_push_cpu_stop+0x13f/0x1a0
[ 1260.960377] ? migration_cpu_stop+0x2b0/0x2b0
[ 1260.960379] cpu_stopper_thread+0xaf/0x140
[ 1260.960382] smpboot_thread_fn+0x158/0x220
[ 1260.960387] ? sort_range+0x30/0x30
[ 1260.960390] kthread+0xfe/0x130
[ 1260.960392] ? kthread_complete_and_exit+0x20/0x20
[ 1260.960394] ret_from_fork+0x1f/0x30
[ 1260.960399] </TASK>
Thanks,
Hao
On Fri, Jun 16, 2023 at 03:56:25PM +0800, Hao Jia wrote: > I'm afraid not, the rq clock also needs to be updated before > select_fallback_rq() is called. > If we just remove update_rq_clock() from __balance_push_cpu_stop(), we will > get this warning. > > > [ 1260.960166] rq->clock_update_flags < RQCF_ACT_SKIP > [ 1260.960170] WARNING: CPU: 25 PID: 196 at kernel/sched/sched.h:1496 > update_curr+0xf6/0x1f0 > > [ 1260.960318] Call Trace: > [ 1260.960320] <TASK> > [ 1260.960359] dequeue_entity+0x3b/0x410 > [ 1260.960361] dequeue_task_fair+0xc7/0x3c0 > [ 1260.960363] dequeue_task+0x30/0xf0 > [ 1260.960365] __do_set_cpus_allowed+0x94/0x130 > [ 1260.960366] do_set_cpus_allowed+0x38/0x60 > [ 1260.960368] cpuset_cpus_allowed_fallback+0x70/0x80 > [ 1260.960372] select_fallback_rq+0x20f/0x250 <---- Urgh... :-(
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 96500560f0c73c71bca1b27536c6254fa0e8ce37
Gitweb: https://git.kernel.org/tip/96500560f0c73c71bca1b27536c6254fa0e8ce37
Author: Hao Jia <jiahao.os@bytedance.com>
AuthorDate: Tue, 13 Jun 2023 16:20:10 +08:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 16 Jun 2023 22:08:12 +02:00
sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()
There is a double update_rq_clock() invocation:
__balance_push_cpu_stop()
update_rq_clock()
__migrate_task()
update_rq_clock()
Sadly select_fallback_rq() also needs update_rq_clock() for
__do_set_cpus_allowed(), it is not possible to remove the update from
__balance_push_cpu_stop(). So remove it from __migrate_task() and
ensure all callers of this function call update_rq_clock() prior to
calling it.
Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20230613082012.49615-3-jiahao.os@bytedance.com
---
kernel/sched/core.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 442efe5..c7db597 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2546,7 +2546,6 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
if (!is_cpu_allowed(p, dest_cpu))
return rq;
- update_rq_clock(rq);
rq = move_queued_task(rq, rf, p, dest_cpu);
return rq;
@@ -2604,10 +2603,12 @@ static int migration_cpu_stop(void *data)
goto out;
}
- if (task_on_rq_queued(p))
+ if (task_on_rq_queued(p)) {
+ update_rq_clock(rq);
rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
- else
+ } else {
p->wake_cpu = arg->dest_cpu;
+ }
/*
* XXX __migrate_task() can fail, at which point we might end
On 2023/6/19 tip-bot2 for Hao Jia wrote:
> The following commit has been merged into the sched/core branch of tip:
>
> Commit-ID: 96500560f0c73c71bca1b27536c6254fa0e8ce37
> Gitweb: https://git.kernel.org/tip/96500560f0c73c71bca1b27536c6254fa0e8ce37
> Author: Hao Jia <jiahao.os@bytedance.com>
> AuthorDate: Tue, 13 Jun 2023 16:20:10 +08:00
> Committer: Peter Zijlstra <peterz@infradead.org>
> CommitterDate: Fri, 16 Jun 2023 22:08:12 +02:00
>
> sched/core: Avoid double calling update_rq_clock() in __balance_push_cpu_stop()
>
> There is a double update_rq_clock() invocation:
>
> __balance_push_cpu_stop()
> update_rq_clock()
> __migrate_task()
> update_rq_clock()
>
> Sadly select_fallback_rq() also needs update_rq_clock() for
> __do_set_cpus_allowed(), it is not possible to remove the update from
> __balance_push_cpu_stop(). So remove it from __migrate_task() and
> ensure all callers of this function call update_rq_clock() prior to
> calling it.
>
Hi Peter,
Thank you very much for refactoring these commit messages to make it
clearer and more concise.
Thanks,
Hao
> Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> Link: https://lkml.kernel.org/r/20230613082012.49615-3-jiahao.os@bytedance.com
> ---
> kernel/sched/core.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 442efe5..c7db597 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2546,7 +2546,6 @@ static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
> if (!is_cpu_allowed(p, dest_cpu))
> return rq;
>
> - update_rq_clock(rq);
> rq = move_queued_task(rq, rf, p, dest_cpu);
>
> return rq;
> @@ -2604,10 +2603,12 @@ static int migration_cpu_stop(void *data)
> goto out;
> }
>
> - if (task_on_rq_queued(p))
> + if (task_on_rq_queued(p)) {
> + update_rq_clock(rq);
> rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
> - else
> + } else {
> p->wake_cpu = arg->dest_cpu;
> + }
>
> /*
> * XXX __migrate_task() can fail, at which point we might end
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