Re: [PATCH v8 -tip 17/26] sched: Split the cookie and setup per-task cookie on fork

Re: [PATCH v8 -tip 17/26] sched: Split the cookie and setup per-task cookie on fork

[chris hyser]

> On 10/19/20 9:43 PM, Joel Fernandes (Google) wrote:
>> In order to prevent interference and clearly support both per-task and CGroup
>> APIs, split the cookie into 2 and allow it to be set from either per-task, or
>> CGroup API. The final cookie is the combined value of both and is computed when
>> the stop-machine executes during a change of cookie.
>>
>> Also, for the per-task cookie, it will get weird if we use pointers of any
>> emphemeral objects. For this reason, introduce a refcounted object who's sole
>> purpose is to assign unique cookie value by way of the object's pointer.
>>
>> While at it, refactor the CGroup code a bit. Future patches will introduce more
>> APIs and support.
>>
>> Tested-by: Julien Desfossez <jdesfossez@digitalocean.com>
>> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
>> ---
>>   include/linux/sched.h |   2 +
>>   kernel/sched/core.c   | 241 ++++++++++++++++++++++++++++++++++++++++--
>>   kernel/sched/debug.c  |   4 +
>>   3 files changed, 236 insertions(+), 11 deletions(-)
>>
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index fe6f225bfbf9..c6034c00846a 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -688,6 +688,8 @@ struct task_struct {
>>   #ifdef CONFIG_SCHED_CORE
>>       struct rb_node            core_node;
>>       unsigned long            core_cookie;
>> +    unsigned long            core_task_cookie;
>> +    unsigned long            core_group_cookie;
>>       unsigned int            core_occupation;
>>   #endif
>>   diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index bab4ea2f5cd8..30a9e4cb5ce1 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -346,11 +346,14 @@ void sched_core_put(void)
>>       mutex_unlock(&sched_core_mutex);
>>   }
>>   +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2);
>> +
>>   #else /* !CONFIG_SCHED_CORE */
>>     static inline void sched_core_enqueue(struct rq *rq, struct task_struct *p) { }
>>   static inline void sched_core_dequeue(struct rq *rq, struct task_struct *p) { }
>>   static bool sched_core_enqueued(struct task_struct *task) { return false; }
>> +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2) { }
>>     #endif /* CONFIG_SCHED_CORE */
>>   @@ -3583,6 +3586,20 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
>>   #endif
>>   #ifdef CONFIG_SCHED_CORE
>>       RB_CLEAR_NODE(&p->core_node);
>> +
>> +    /*
>> +     * Tag child via per-task cookie only if parent is tagged via per-task
>> +     * cookie. This is independent of, but can be additive to the CGroup tagging.
>> +     */
>> +    if (current->core_task_cookie) {
>> +
>> +        /* If it is not CLONE_THREAD fork, assign a unique per-task tag. */
>> +        if (!(clone_flags & CLONE_THREAD)) {
>> +            return sched_core_share_tasks(p, p);
>> +               }
>> +        /* Otherwise share the parent's per-task tag. */
>> +        return sched_core_share_tasks(p, current);
>> +    }
>>   #endif
>>       return 0;
>>   } 

sched_core_share_tasks() looks at the value of the new tasks core_task_cookie which is non-zero on a
process or thread clone and causes underflow for both the enable flag itself and for cookie ref counts.

So just zero it in __sched_fork().

-chris


PATCH] sched: zero out the core scheduling cookie on clone

From: chris hyser <chris.hyser@oracle.com>

As the cookie is reference counted, even if inherited, zero this and allow
explicit sharing.

Signed-off-by: Chris Hyser <chris.hyser@oracle.com>
---
  kernel/sched/core.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fd3cc03..2af0ea6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3378,6 +3378,9 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
  	p->capture_control = NULL;
  #endif
  	init_numa_balancing(clone_flags, p);
+#ifdef CONFIG_SCHED_CORE
+	p->core_task_cookie = 0;
+#endif
  #ifdef CONFIG_SMP
  	p->wake_entry.u_flags = CSD_TYPE_TTWU;
  #endif
-- 
1.8.3.1

Re: [PATCH v8 -tip 17/26] sched: Split the cookie and setup per-task cookie on fork

[Joel Fernandes]

On Mon, Nov 09, 2020 at 06:23:13PM -0500, chris hyser wrote:
[..]
> > 
> > > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > > index fe6f225bfbf9..c6034c00846a 100644
> > > --- a/include/linux/sched.h
> > > +++ b/include/linux/sched.h
> > > @@ -688,6 +688,8 @@ struct task_struct {
> > >   #ifdef CONFIG_SCHED_CORE
> > >       struct rb_node            core_node;
> > >       unsigned long            core_cookie;
> > > +    unsigned long            core_task_cookie;
> > > +    unsigned long            core_group_cookie;
> > >       unsigned int            core_occupation;
> > >   #endif
> > >   diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > > index bab4ea2f5cd8..30a9e4cb5ce1 100644
> > > --- a/kernel/sched/core.c
> > > +++ b/kernel/sched/core.c
> > > @@ -346,11 +346,14 @@ void sched_core_put(void)
> > >       mutex_unlock(&sched_core_mutex);
> > >   }
> > >   +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2);
> > > +
> > >   #else /* !CONFIG_SCHED_CORE */
> > >     static inline void sched_core_enqueue(struct rq *rq, struct task_struct *p) { }
> > >   static inline void sched_core_dequeue(struct rq *rq, struct task_struct *p) { }
> > >   static bool sched_core_enqueued(struct task_struct *task) { return false; }
> > > +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2) { }
> > >     #endif /* CONFIG_SCHED_CORE */
> > >   @@ -3583,6 +3586,20 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
> > >   #endif
> > >   #ifdef CONFIG_SCHED_CORE
> > >       RB_CLEAR_NODE(&p->core_node);
> > > +
> > > +    /*
> > > +     * Tag child via per-task cookie only if parent is tagged via per-task
> > > +     * cookie. This is independent of, but can be additive to the CGroup tagging.
> > > +     */
> > > +    if (current->core_task_cookie) {
> > > +
> > > +        /* If it is not CLONE_THREAD fork, assign a unique per-task tag. */
> > > +        if (!(clone_flags & CLONE_THREAD)) {
> > > +            return sched_core_share_tasks(p, p);
> > > +               }
> > > +        /* Otherwise share the parent's per-task tag. */
> > > +        return sched_core_share_tasks(p, current);
> > > +    }
> > >   #endif
> > >       return 0;
> > >   }
> 
> sched_core_share_tasks() looks at the value of the new tasks core_task_cookie which is non-zero on a
> process or thread clone and causes underflow for both the enable flag itself and for cookie ref counts.
> 
> So just zero it in __sched_fork().

Nice catch, applying to my v9 staging tree. Thanks!

thanks,

 - Joel


> 
> -chris
> 
> 
> PATCH] sched: zero out the core scheduling cookie on clone
> 
> From: chris hyser <chris.hyser@oracle.com>
> 
> As the cookie is reference counted, even if inherited, zero this and allow
> explicit sharing.
> 
> Signed-off-by: Chris Hyser <chris.hyser@oracle.com>
> ---
>  kernel/sched/core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index fd3cc03..2af0ea6 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3378,6 +3378,9 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
>  	p->capture_control = NULL;
>  #endif
>  	init_numa_balancing(clone_flags, p);
> +#ifdef CONFIG_SCHED_CORE
> +	p->core_task_cookie = 0;
> +#endif
>  #ifdef CONFIG_SMP
>  	p->wake_entry.u_flags = CSD_TYPE_TTWU;
>  #endif
> -- 
> 1.8.3.1
> 

Re: [PATCH v8 -tip 17/26] sched: Split the cookie and setup per-task cookie on fork

[Joel Fernandes]

Hi Chris,

On Mon, Nov 09, 2020 at 06:23:13PM -0500, chris hyser wrote:
> > On 10/19/20 9:43 PM, Joel Fernandes (Google) wrote:
> > > In order to prevent interference and clearly support both per-task and CGroup
> > > APIs, split the cookie into 2 and allow it to be set from either per-task, or
> > > CGroup API. The final cookie is the combined value of both and is computed when
> > > the stop-machine executes during a change of cookie.
> > > 
> > > Also, for the per-task cookie, it will get weird if we use pointers of any
> > > emphemeral objects. For this reason, introduce a refcounted object who's sole
> > > purpose is to assign unique cookie value by way of the object's pointer.
> > > 
> > > While at it, refactor the CGroup code a bit. Future patches will introduce more
> > > APIs and support.
> > > 
> > > Tested-by: Julien Desfossez <jdesfossez@digitalocean.com>
> > > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > > ---
> > >   include/linux/sched.h |   2 +
> > >   kernel/sched/core.c   | 241 ++++++++++++++++++++++++++++++++++++++++--
> > >   kernel/sched/debug.c  |   4 +
> > >   3 files changed, 236 insertions(+), 11 deletions(-)
> > > 
> > > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > > index fe6f225bfbf9..c6034c00846a 100644
> > > --- a/include/linux/sched.h
> > > +++ b/include/linux/sched.h
> > > @@ -688,6 +688,8 @@ struct task_struct {
> > >   #ifdef CONFIG_SCHED_CORE
> > >       struct rb_node            core_node;
> > >       unsigned long            core_cookie;
> > > +    unsigned long            core_task_cookie;
> > > +    unsigned long            core_group_cookie;
> > >       unsigned int            core_occupation;
> > >   #endif
> > >   diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > > index bab4ea2f5cd8..30a9e4cb5ce1 100644
> > > --- a/kernel/sched/core.c
> > > +++ b/kernel/sched/core.c
> > > @@ -346,11 +346,14 @@ void sched_core_put(void)
> > >       mutex_unlock(&sched_core_mutex);
> > >   }
> > >   +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2);
> > > +
> > >   #else /* !CONFIG_SCHED_CORE */
> > >     static inline void sched_core_enqueue(struct rq *rq, struct task_struct *p) { }
> > >   static inline void sched_core_dequeue(struct rq *rq, struct task_struct *p) { }
> > >   static bool sched_core_enqueued(struct task_struct *task) { return false; }
> > > +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2) { }
> > >     #endif /* CONFIG_SCHED_CORE */
> > >   @@ -3583,6 +3586,20 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
> > >   #endif
> > >   #ifdef CONFIG_SCHED_CORE
> > >       RB_CLEAR_NODE(&p->core_node);
> > > +
> > > +    /*
> > > +     * Tag child via per-task cookie only if parent is tagged via per-task
> > > +     * cookie. This is independent of, but can be additive to the CGroup tagging.
> > > +     */
> > > +    if (current->core_task_cookie) {
> > > +
> > > +        /* If it is not CLONE_THREAD fork, assign a unique per-task tag. */
> > > +        if (!(clone_flags & CLONE_THREAD)) {
> > > +            return sched_core_share_tasks(p, p);
> > > +               }
> > > +        /* Otherwise share the parent's per-task tag. */
> > > +        return sched_core_share_tasks(p, current);
> > > +    }
> > >   #endif
> > >       return 0;
> > >   }
> 
> sched_core_share_tasks() looks at the value of the new tasks core_task_cookie which is non-zero on a
> process or thread clone and causes underflow for both the enable flag itself and for cookie ref counts.
> 
> So just zero it in __sched_fork().

Since I am going to split this into a new patch, could you please send me a
detailed commit message explaining the issue? I feel the below one liner is
unclear / insufficient as a commit message.

thanks,

 - Joel


> -chris
> 
> 
> PATCH] sched: zero out the core scheduling cookie on clone
> 
> From: chris hyser <chris.hyser@oracle.com>
> 
> As the cookie is reference counted, even if inherited, zero this and allow
> explicit sharing.
> 
> Signed-off-by: Chris Hyser <chris.hyser@oracle.com>
> ---
>  kernel/sched/core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index fd3cc03..2af0ea6 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3378,6 +3378,9 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
>  	p->capture_control = NULL;
>  #endif
>  	init_numa_balancing(clone_flags, p);
> +#ifdef CONFIG_SCHED_CORE
> +	p->core_task_cookie = 0;
> +#endif
>  #ifdef CONFIG_SMP
>  	p->wake_entry.u_flags = CSD_TYPE_TTWU;
>  #endif
> -- 
> 1.8.3.1
> 

Re: [PATCH v8 -tip 17/26] sched: Split the cookie and setup per-task cookie on fork

[chris hyser]

On 11/4/20 5:30 PM, chris hyser wrote:
> On 10/19/20 9:43 PM, Joel Fernandes (Google) wrote:
>> In order to prevent interference and clearly support both per-task and CGroup
>> APIs, split the cookie into 2 and allow it to be set from either per-task, or
>> CGroup API. The final cookie is the combined value of both and is computed when
>> the stop-machine executes during a change of cookie.
>>
>> Also, for the per-task cookie, it will get weird if we use pointers of any
>> emphemeral objects. For this reason, introduce a refcounted object who's sole
>> purpose is to assign unique cookie value by way of the object's pointer.
>>
>> While at it, refactor the CGroup code a bit. Future patches will introduce more
>> APIs and support.
>>
>> Tested-by: Julien Desfossez <jdesfossez@digitalocean.com>
>> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
>> ---
>>   include/linux/sched.h |   2 +
>>   kernel/sched/core.c   | 241 ++++++++++++++++++++++++++++++++++++++++--
>>   kernel/sched/debug.c  |   4 +
>>   3 files changed, 236 insertions(+), 11 deletions(-)
>>
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index fe6f225bfbf9..c6034c00846a 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -688,6 +688,8 @@ struct task_struct {
>>   #ifdef CONFIG_SCHED_CORE
>>       struct rb_node            core_node;
>>       unsigned long            core_cookie;
>> +    unsigned long            core_task_cookie;
>> +    unsigned long            core_group_cookie;
>>       unsigned int            core_occupation;
>>   #endif
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index bab4ea2f5cd8..30a9e4cb5ce1 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -346,11 +346,14 @@ void sched_core_put(void)
>>       mutex_unlock(&sched_core_mutex);
>>   }
>> +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2);
>> +
>>   #else /* !CONFIG_SCHED_CORE */
>>   static inline void sched_core_enqueue(struct rq *rq, struct task_struct *p) { }
>>   static inline void sched_core_dequeue(struct rq *rq, struct task_struct *p) { }
>>   static bool sched_core_enqueued(struct task_struct *task) { return false; }
>> +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2) { }
>>   #endif /* CONFIG_SCHED_CORE */
>> @@ -3583,6 +3586,20 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
>>   #endif
>>   #ifdef CONFIG_SCHED_CORE
>>       RB_CLEAR_NODE(&p->core_node);
>> +
>> +    /*
>> +     * Tag child via per-task cookie only if parent is tagged via per-task
>> +     * cookie. This is independent of, but can be additive to the CGroup tagging.
>> +     */
>> +    if (current->core_task_cookie) {
>> +
>> +        /* If it is not CLONE_THREAD fork, assign a unique per-task tag. */
>> +        if (!(clone_flags & CLONE_THREAD)) {
>> +            return sched_core_share_tasks(p, p);
>> +               }
>> +        /* Otherwise share the parent's per-task tag. */
>> +        return sched_core_share_tasks(p, current);
>> +    }
>>   #endif
>>       return 0;
>>   }

sched_core_share_tasks() looks at the value of the new tasks core_task_cookie which is non-zero on a
process or thread clone and causes underflow for both the enable flag itself and for cookie ref counts.

So just zero it in __sched_fork().

-chrish

------

sched: zero out the core scheduling cookie on clone

As the cookie is reference counted, even if inherited, zero this and allow
explicit sharing.

Signed-off-by: Chris Hyser <chris.hyser@oracle.com>
---
  kernel/sched/core.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fd3cc03..2af0ea6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3378,6 +3378,9 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
      p->capture_control = NULL;
  #endif
      init_numa_balancing(clone_flags, p);
+#ifdef CONFIG_SCHED_CORE
+    p->core_task_cookie = 0;
+#endif
  #ifdef CONFIG_SMP
      p->wake_entry.u_flags = CSD_TYPE_TTWU;
  #endif

Re: [PATCH v8 -tip 17/26] sched: Split the cookie and setup per-task cookie on fork

[Joel Fernandes]

On Wed, Nov 04, 2020 at 05:30:24PM -0500, chris hyser wrote:
[..]
> +		wr.cookies[0] = cookie;
> > +	} else
> > +	/*
> > +	 * 		t1		joining		t2
> > +	 * CASE 1:
> > +	 * before	0				0
> > +	 * after	new cookie			new cookie
> > +	 *
> > +	 * CASE 2:
> > +	 * before	X (non-zero)			0
> > +	 * after	0				0
> > +	 *
> > +	 * CASE 3:
> > +	 * before	0				X (non-zero)
> > +	 * after	X				X
> > +	 *
> > +	 * CASE 4:
> > +	 * before	Y (non-zero)			X (non-zero)
> > +	 * after	X				X
> > +	 */
> > +	if (!t1->core_task_cookie && !t2->core_task_cookie) {
> > +		/* CASE 1. */
> > +		cookie = sched_core_alloc_task_cookie();
> > +		if (!cookie)
> > +			goto out_unlock;
> > +
> > +		/* Add another reference for the other task. */
> > +		if (!sched_core_get_task_cookie(cookie)) {
> > +			return -EINVAL;
> 
> should be:              ret = -EINVAL;

Fixed now, thanks.

thanks,

 - Joel


> 
> > +			goto out_unlock;
> > +		}
> > +
> > +		wr.tasks[0] = t1;
> > +		wr.tasks[1] = t2;
> > +		wr.cookies[0] = wr.cookies[1] = cookie;
> > +
> > +	} else if (t1->core_task_cookie && !t2->core_task_cookie) {
> > +		/* CASE 2. */
> > +		sched_core_put_task_cookie(t1->core_task_cookie);
> > +		sched_core_put_after_stopper = true;
> > +
> > +		wr.tasks[0] = t1; /* Reset cookie for t1. */
> > +
> > +	} else if (!t1->core_task_cookie && t2->core_task_cookie) {
> > +		/* CASE 3. */
> > +		if (!sched_core_get_task_cookie(t2->core_task_cookie)) {
> > +			ret = -EINVAL;
> > +			goto out_unlock;
> > +		}
> > +
> > +		wr.tasks[0] = t1;
> > +		wr.cookies[0] = t2->core_task_cookie;
> > +
> > +	} else {
> > +		/* CASE 4. */
> > +		if (!sched_core_get_task_cookie(t2->core_task_cookie)) {
> > +			ret = -EINVAL;
> > +			goto out_unlock;
> > +		}
> > +		sched_core_put_task_cookie(t1->core_task_cookie);
> > +		sched_core_put_after_stopper = true;
> > +
> > +		wr.tasks[0] = t1;
> > +		wr.cookies[0] = t2->core_task_cookie;
> > +	}
> > +
> > +	stop_machine(sched_core_task_join_stopper, (void *)&wr, NULL);
> > +
> > +	if (sched_core_put_after_stopper)
> > +		sched_core_put();
> > +
> > +	ret = 0;
> > +out_unlock:
> > +	mutex_unlock(&sched_core_mutex);
> > +	return ret;
> > +}
> > +
> > +/* CGroup interface */
> >   static u64 cpu_core_tag_read_u64(struct cgroup_subsys_state *css, struct cftype *cft)
> >   {
> >   	struct task_group *tg = css_tg(css);
> > @@ -9207,18 +9435,9 @@ static int __sched_write_tag(void *data)
> >   	 * when we set cgroup tag to 0 when the loop is done below.
> >   	 */
> >   	while ((p = css_task_iter_next(&it))) {
> > -		p->core_cookie = !!val ? (unsigned long)tg : 0UL;
> > -
> > -		if (sched_core_enqueued(p)) {
> > -			sched_core_dequeue(task_rq(p), p);
> > -			if (!p->core_cookie)
> > -				continue;
> > -		}
> > -
> > -		if (sched_core_enabled(task_rq(p)) &&
> > -		    p->core_cookie && task_on_rq_queued(p))
> > -			sched_core_enqueue(task_rq(p), p);
> > +		unsigned long cookie = !!val ? (unsigned long)tg : 0UL;
> > +		sched_core_tag_requeue(p, cookie, true /* group */);
> >   	}
> >   	css_task_iter_end(&it);
> > diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> > index c8fee8d9dfd4..88bf45267672 100644
> > --- a/kernel/sched/debug.c
> > +++ b/kernel/sched/debug.c
> > @@ -1024,6 +1024,10 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
> >   		__PS("clock-delta", t1-t0);
> >   	}
> > +#ifdef CONFIG_SCHED_CORE
> > +	__PS("core_cookie", p->core_cookie);
> > +#endif
> > +
> >   	sched_show_numa(p, m);
> >   }
> > 
> 
> -chrish

Re: [PATCH v8 -tip 17/26] sched: Split the cookie and setup per-task cookie on fork

[chris hyser]

On 10/19/20 9:43 PM, Joel Fernandes (Google) wrote:
> In order to prevent interference and clearly support both per-task and CGroup
> APIs, split the cookie into 2 and allow it to be set from either per-task, or
> CGroup API. The final cookie is the combined value of both and is computed when
> the stop-machine executes during a change of cookie.
> 
> Also, for the per-task cookie, it will get weird if we use pointers of any
> emphemeral objects. For this reason, introduce a refcounted object who's sole
> purpose is to assign unique cookie value by way of the object's pointer.
> 
> While at it, refactor the CGroup code a bit. Future patches will introduce more
> APIs and support.
> 
> Tested-by: Julien Desfossez <jdesfossez@digitalocean.com>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> ---
>   include/linux/sched.h |   2 +
>   kernel/sched/core.c   | 241 ++++++++++++++++++++++++++++++++++++++++--
>   kernel/sched/debug.c  |   4 +
>   3 files changed, 236 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index fe6f225bfbf9..c6034c00846a 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -688,6 +688,8 @@ struct task_struct {
>   #ifdef CONFIG_SCHED_CORE
>   	struct rb_node			core_node;
>   	unsigned long			core_cookie;
> +	unsigned long			core_task_cookie;
> +	unsigned long			core_group_cookie;
>   	unsigned int			core_occupation;
>   #endif
>   
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index bab4ea2f5cd8..30a9e4cb5ce1 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -346,11 +346,14 @@ void sched_core_put(void)
>   	mutex_unlock(&sched_core_mutex);
>   }
>   
> +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2);
> +
>   #else /* !CONFIG_SCHED_CORE */
>   
>   static inline void sched_core_enqueue(struct rq *rq, struct task_struct *p) { }
>   static inline void sched_core_dequeue(struct rq *rq, struct task_struct *p) { }
>   static bool sched_core_enqueued(struct task_struct *task) { return false; }
> +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2) { }
>   
>   #endif /* CONFIG_SCHED_CORE */
>   
> @@ -3583,6 +3586,20 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
>   #endif
>   #ifdef CONFIG_SCHED_CORE
>   	RB_CLEAR_NODE(&p->core_node);
> +
> +	/*
> +	 * Tag child via per-task cookie only if parent is tagged via per-task
> +	 * cookie. This is independent of, but can be additive to the CGroup tagging.
> +	 */
> +	if (current->core_task_cookie) {
> +
> +		/* If it is not CLONE_THREAD fork, assign a unique per-task tag. */
> +		if (!(clone_flags & CLONE_THREAD)) {
> +			return sched_core_share_tasks(p, p);
> +               }
> +		/* Otherwise share the parent's per-task tag. */
> +		return sched_core_share_tasks(p, current);
> +	}
>   #endif
>   	return 0;
>   }
> @@ -9177,6 +9194,217 @@ static u64 cpu_rt_period_read_uint(struct cgroup_subsys_state *css,
>   #endif /* CONFIG_RT_GROUP_SCHED */
>   
>   #ifdef CONFIG_SCHED_CORE
> +/*
> + * A simple wrapper around refcount. An allocated sched_core_cookie's
> + * address is used to compute the cookie of the task.
> + */
> +struct sched_core_cookie {
> +	refcount_t refcnt;
> +};
> +
> +/*
> + * sched_core_tag_requeue - Common helper for all interfaces to set a cookie.
> + * @p: The task to assign a cookie to.
> + * @cookie: The cookie to assign.
> + * @group: is it a group interface or a per-task interface.
> + *
> + * This function is typically called from a stop-machine handler.
> + */
> +void sched_core_tag_requeue(struct task_struct *p, unsigned long cookie, bool group)
> +{
> +	if (!p)
> +		return;
> +
> +	if (group)
> +		p->core_group_cookie = cookie;
> +	else
> +		p->core_task_cookie = cookie;
> +
> +	/* Use up half of the cookie's bits for task cookie and remaining for group cookie. */
> +	p->core_cookie = (p->core_task_cookie <<
> +				(sizeof(unsigned long) * 4)) + p->core_group_cookie;
> +
> +	if (sched_core_enqueued(p)) {
> +		sched_core_dequeue(task_rq(p), p);
> +		if (!p->core_task_cookie)
> +			return;
> +	}
> +
> +	if (sched_core_enabled(task_rq(p)) &&
> +			p->core_cookie && task_on_rq_queued(p))
> +		sched_core_enqueue(task_rq(p), p);
> +}
> +
> +/* Per-task interface */
> +static unsigned long sched_core_alloc_task_cookie(void)
> +{
> +	struct sched_core_cookie *ptr =
> +		kmalloc(sizeof(struct sched_core_cookie), GFP_KERNEL);
> +
> +	if (!ptr)
> +		return 0;
> +	refcount_set(&ptr->refcnt, 1);
> +
> +	/*
> +	 * NOTE: sched_core_put() is not done by put_task_cookie(). Instead, it
> +	 * is done after the stopper runs.
> +	 */
> +	sched_core_get();
> +	return (unsigned long)ptr;
> +}
> +
> +static bool sched_core_get_task_cookie(unsigned long cookie)
> +{
> +	struct sched_core_cookie *ptr = (struct sched_core_cookie *)cookie;
> +
> +	/*
> +	 * NOTE: sched_core_put() is not done by put_task_cookie(). Instead, it
> +	 * is done after the stopper runs.
> +	 */
> +	sched_core_get();
> +	return refcount_inc_not_zero(&ptr->refcnt);
> +}
> +
> +static void sched_core_put_task_cookie(unsigned long cookie)
> +{
> +	struct sched_core_cookie *ptr = (struct sched_core_cookie *)cookie;
> +
> +	if (refcount_dec_and_test(&ptr->refcnt))
> +		kfree(ptr);
> +}
> +
> +struct sched_core_task_write_tag {
> +	struct task_struct *tasks[2];
> +	unsigned long cookies[2];
> +};
> +
> +/*
> + * Ensure that the task has been requeued. The stopper ensures that the task cannot
> + * be migrated to a different CPU while its core scheduler queue state is being updated.
> + * It also makes sure to requeue a task if it was running actively on another CPU.
> + */
> +static int sched_core_task_join_stopper(void *data)
> +{
> +	struct sched_core_task_write_tag *tag = (struct sched_core_task_write_tag *)data;
> +	int i;
> +
> +	for (i = 0; i < 2; i++)
> +		sched_core_tag_requeue(tag->tasks[i], tag->cookies[i], false /* !group */);
> +
> +	return 0;
> +}
> +
> +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2)
> +{
> +	struct sched_core_task_write_tag wr = {}; /* for stop machine. */
> +	bool sched_core_put_after_stopper = false;
> +	unsigned long cookie;
> +	int ret = -ENOMEM;
> +
> +	mutex_lock(&sched_core_mutex);
> +
> +	/*
> +	 * NOTE: sched_core_get() is done by sched_core_alloc_task_cookie() or
> +	 *       sched_core_put_task_cookie(). However, sched_core_put() is done
> +	 *       by this function *after* the stopper removes the tasks from the
> +	 *       core queue, and not before. This is just to play it safe.
> +	 */
> +	if (t2 == NULL) {
> +		if (t1->core_task_cookie) {
> +			sched_core_put_task_cookie(t1->core_task_cookie);
> +			sched_core_put_after_stopper = true;
> +			wr.tasks[0] = t1; /* Keep wr.cookies[0] reset for t1. */
> +		}
> +	} else if (t1 == t2) {
> +		/* Assign a unique per-task cookie solely for t1. */
> +
> +		cookie = sched_core_alloc_task_cookie();
> +		if (!cookie)
> +			goto out_unlock;
> +
> +		if (t1->core_task_cookie) {
> +			sched_core_put_task_cookie(t1->core_task_cookie);
> +			sched_core_put_after_stopper = true;
> +		}
> +		wr.tasks[0] = t1;
> +		wr.cookies[0] = cookie;
> +	} else
> +	/*
> +	 * 		t1		joining		t2
> +	 * CASE 1:
> +	 * before	0				0
> +	 * after	new cookie			new cookie
> +	 *
> +	 * CASE 2:
> +	 * before	X (non-zero)			0
> +	 * after	0				0
> +	 *
> +	 * CASE 3:
> +	 * before	0				X (non-zero)
> +	 * after	X				X
> +	 *
> +	 * CASE 4:
> +	 * before	Y (non-zero)			X (non-zero)
> +	 * after	X				X
> +	 */
> +	if (!t1->core_task_cookie && !t2->core_task_cookie) {
> +		/* CASE 1. */
> +		cookie = sched_core_alloc_task_cookie();
> +		if (!cookie)
> +			goto out_unlock;
> +
> +		/* Add another reference for the other task. */
> +		if (!sched_core_get_task_cookie(cookie)) {
> +			return -EINVAL;

should be:              ret = -EINVAL;

> +			goto out_unlock;
> +		}
> +
> +		wr.tasks[0] = t1;
> +		wr.tasks[1] = t2;
> +		wr.cookies[0] = wr.cookies[1] = cookie;
> +
> +	} else if (t1->core_task_cookie && !t2->core_task_cookie) {
> +		/* CASE 2. */
> +		sched_core_put_task_cookie(t1->core_task_cookie);
> +		sched_core_put_after_stopper = true;
> +
> +		wr.tasks[0] = t1; /* Reset cookie for t1. */
> +
> +	} else if (!t1->core_task_cookie && t2->core_task_cookie) {
> +		/* CASE 3. */
> +		if (!sched_core_get_task_cookie(t2->core_task_cookie)) {
> +			ret = -EINVAL;
> +			goto out_unlock;
> +		}
> +
> +		wr.tasks[0] = t1;
> +		wr.cookies[0] = t2->core_task_cookie;
> +
> +	} else {
> +		/* CASE 4. */
> +		if (!sched_core_get_task_cookie(t2->core_task_cookie)) {
> +			ret = -EINVAL;
> +			goto out_unlock;
> +		}
> +		sched_core_put_task_cookie(t1->core_task_cookie);
> +		sched_core_put_after_stopper = true;
> +
> +		wr.tasks[0] = t1;
> +		wr.cookies[0] = t2->core_task_cookie;
> +	}
> +
> +	stop_machine(sched_core_task_join_stopper, (void *)&wr, NULL);
> +
> +	if (sched_core_put_after_stopper)
> +		sched_core_put();
> +
> +	ret = 0;
> +out_unlock:
> +	mutex_unlock(&sched_core_mutex);
> +	return ret;
> +}
> +
> +/* CGroup interface */
>   static u64 cpu_core_tag_read_u64(struct cgroup_subsys_state *css, struct cftype *cft)
>   {
>   	struct task_group *tg = css_tg(css);
> @@ -9207,18 +9435,9 @@ static int __sched_write_tag(void *data)
>   	 * when we set cgroup tag to 0 when the loop is done below.
>   	 */
>   	while ((p = css_task_iter_next(&it))) {
> -		p->core_cookie = !!val ? (unsigned long)tg : 0UL;
> -
> -		if (sched_core_enqueued(p)) {
> -			sched_core_dequeue(task_rq(p), p);
> -			if (!p->core_cookie)
> -				continue;
> -		}
> -
> -		if (sched_core_enabled(task_rq(p)) &&
> -		    p->core_cookie && task_on_rq_queued(p))
> -			sched_core_enqueue(task_rq(p), p);
> +		unsigned long cookie = !!val ? (unsigned long)tg : 0UL;
>   
> +		sched_core_tag_requeue(p, cookie, true /* group */);
>   	}
>   	css_task_iter_end(&it);
>   
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index c8fee8d9dfd4..88bf45267672 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -1024,6 +1024,10 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
>   		__PS("clock-delta", t1-t0);
>   	}
>   
> +#ifdef CONFIG_SCHED_CORE
> +	__PS("core_cookie", p->core_cookie);
> +#endif
> +
>   	sched_show_numa(p, m);
>   }
>   
> 

-chrish

[PATCH v8 -tip 17/26] sched: Split the cookie and setup per-task cookie on fork

[Joel Fernandes (Google)]

In order to prevent interference and clearly support both per-task and CGroup
APIs, split the cookie into 2 and allow it to be set from either per-task, or
CGroup API. The final cookie is the combined value of both and is computed when
the stop-machine executes during a change of cookie.

Also, for the per-task cookie, it will get weird if we use pointers of any
emphemeral objects. For this reason, introduce a refcounted object who's sole
purpose is to assign unique cookie value by way of the object's pointer.

While at it, refactor the CGroup code a bit. Future patches will introduce more
APIs and support.

Tested-by: Julien Desfossez <jdesfossez@digitalocean.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 include/linux/sched.h |   2 +
 kernel/sched/core.c   | 241 ++++++++++++++++++++++++++++++++++++++++--
 kernel/sched/debug.c  |   4 +
 3 files changed, 236 insertions(+), 11 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index fe6f225bfbf9..c6034c00846a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -688,6 +688,8 @@ struct task_struct {
 #ifdef CONFIG_SCHED_CORE
 	struct rb_node			core_node;
 	unsigned long			core_cookie;
+	unsigned long			core_task_cookie;
+	unsigned long			core_group_cookie;
 	unsigned int			core_occupation;
 #endif
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bab4ea2f5cd8..30a9e4cb5ce1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -346,11 +346,14 @@ void sched_core_put(void)
 	mutex_unlock(&sched_core_mutex);
 }
 
+static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2);
+
 #else /* !CONFIG_SCHED_CORE */
 
 static inline void sched_core_enqueue(struct rq *rq, struct task_struct *p) { }
 static inline void sched_core_dequeue(struct rq *rq, struct task_struct *p) { }
 static bool sched_core_enqueued(struct task_struct *task) { return false; }
+static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2) { }
 
 #endif /* CONFIG_SCHED_CORE */
 
@@ -3583,6 +3586,20 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 #endif
 #ifdef CONFIG_SCHED_CORE
 	RB_CLEAR_NODE(&p->core_node);
+
+	/*
+	 * Tag child via per-task cookie only if parent is tagged via per-task
+	 * cookie. This is independent of, but can be additive to the CGroup tagging.
+	 */
+	if (current->core_task_cookie) {
+
+		/* If it is not CLONE_THREAD fork, assign a unique per-task tag. */
+		if (!(clone_flags & CLONE_THREAD)) {
+			return sched_core_share_tasks(p, p);
+               }
+		/* Otherwise share the parent's per-task tag. */
+		return sched_core_share_tasks(p, current);
+	}
 #endif
 	return 0;
 }
@@ -9177,6 +9194,217 @@ static u64 cpu_rt_period_read_uint(struct cgroup_subsys_state *css,
 #endif /* CONFIG_RT_GROUP_SCHED */
 
 #ifdef CONFIG_SCHED_CORE
+/*
+ * A simple wrapper around refcount. An allocated sched_core_cookie's
+ * address is used to compute the cookie of the task.
+ */
+struct sched_core_cookie {
+	refcount_t refcnt;
+};
+
+/*
+ * sched_core_tag_requeue - Common helper for all interfaces to set a cookie.
+ * @p: The task to assign a cookie to.
+ * @cookie: The cookie to assign.
+ * @group: is it a group interface or a per-task interface.
+ *
+ * This function is typically called from a stop-machine handler.
+ */
+void sched_core_tag_requeue(struct task_struct *p, unsigned long cookie, bool group)
+{
+	if (!p)
+		return;
+
+	if (group)
+		p->core_group_cookie = cookie;
+	else
+		p->core_task_cookie = cookie;
+
+	/* Use up half of the cookie's bits for task cookie and remaining for group cookie. */
+	p->core_cookie = (p->core_task_cookie <<
+				(sizeof(unsigned long) * 4)) + p->core_group_cookie;
+
+	if (sched_core_enqueued(p)) {
+		sched_core_dequeue(task_rq(p), p);
+		if (!p->core_task_cookie)
+			return;
+	}
+
+	if (sched_core_enabled(task_rq(p)) &&
+			p->core_cookie && task_on_rq_queued(p))
+		sched_core_enqueue(task_rq(p), p);
+}
+
+/* Per-task interface */
+static unsigned long sched_core_alloc_task_cookie(void)
+{
+	struct sched_core_cookie *ptr =
+		kmalloc(sizeof(struct sched_core_cookie), GFP_KERNEL);
+
+	if (!ptr)
+		return 0;
+	refcount_set(&ptr->refcnt, 1);
+
+	/*
+	 * NOTE: sched_core_put() is not done by put_task_cookie(). Instead, it
+	 * is done after the stopper runs.
+	 */
+	sched_core_get();
+	return (unsigned long)ptr;
+}
+
+static bool sched_core_get_task_cookie(unsigned long cookie)
+{
+	struct sched_core_cookie *ptr = (struct sched_core_cookie *)cookie;
+
+	/*
+	 * NOTE: sched_core_put() is not done by put_task_cookie(). Instead, it
+	 * is done after the stopper runs.
+	 */
+	sched_core_get();
+	return refcount_inc_not_zero(&ptr->refcnt);
+}
+
+static void sched_core_put_task_cookie(unsigned long cookie)
+{
+	struct sched_core_cookie *ptr = (struct sched_core_cookie *)cookie;
+
+	if (refcount_dec_and_test(&ptr->refcnt))
+		kfree(ptr);
+}
+
+struct sched_core_task_write_tag {
+	struct task_struct *tasks[2];
+	unsigned long cookies[2];
+};
+
+/*
+ * Ensure that the task has been requeued. The stopper ensures that the task cannot
+ * be migrated to a different CPU while its core scheduler queue state is being updated.
+ * It also makes sure to requeue a task if it was running actively on another CPU.
+ */
+static int sched_core_task_join_stopper(void *data)
+{
+	struct sched_core_task_write_tag *tag = (struct sched_core_task_write_tag *)data;
+	int i;
+
+	for (i = 0; i < 2; i++)
+		sched_core_tag_requeue(tag->tasks[i], tag->cookies[i], false /* !group */);
+
+	return 0;
+}
+
+static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2)
+{
+	struct sched_core_task_write_tag wr = {}; /* for stop machine. */
+	bool sched_core_put_after_stopper = false;
+	unsigned long cookie;
+	int ret = -ENOMEM;
+
+	mutex_lock(&sched_core_mutex);
+
+	/*
+	 * NOTE: sched_core_get() is done by sched_core_alloc_task_cookie() or
+	 *       sched_core_put_task_cookie(). However, sched_core_put() is done
+	 *       by this function *after* the stopper removes the tasks from the
+	 *       core queue, and not before. This is just to play it safe.
+	 */
+	if (t2 == NULL) {
+		if (t1->core_task_cookie) {
+			sched_core_put_task_cookie(t1->core_task_cookie);
+			sched_core_put_after_stopper = true;
+			wr.tasks[0] = t1; /* Keep wr.cookies[0] reset for t1. */
+		}
+	} else if (t1 == t2) {
+		/* Assign a unique per-task cookie solely for t1. */
+
+		cookie = sched_core_alloc_task_cookie();
+		if (!cookie)
+			goto out_unlock;
+
+		if (t1->core_task_cookie) {
+			sched_core_put_task_cookie(t1->core_task_cookie);
+			sched_core_put_after_stopper = true;
+		}
+		wr.tasks[0] = t1;
+		wr.cookies[0] = cookie;
+	} else
+	/*
+	 * 		t1		joining		t2
+	 * CASE 1:
+	 * before	0				0
+	 * after	new cookie			new cookie
+	 *
+	 * CASE 2:
+	 * before	X (non-zero)			0
+	 * after	0				0
+	 *
+	 * CASE 3:
+	 * before	0				X (non-zero)
+	 * after	X				X
+	 *
+	 * CASE 4:
+	 * before	Y (non-zero)			X (non-zero)
+	 * after	X				X
+	 */
+	if (!t1->core_task_cookie && !t2->core_task_cookie) {
+		/* CASE 1. */
+		cookie = sched_core_alloc_task_cookie();
+		if (!cookie)
+			goto out_unlock;
+
+		/* Add another reference for the other task. */
+		if (!sched_core_get_task_cookie(cookie)) {
+			return -EINVAL;
+			goto out_unlock;
+		}
+
+		wr.tasks[0] = t1;
+		wr.tasks[1] = t2;
+		wr.cookies[0] = wr.cookies[1] = cookie;
+
+	} else if (t1->core_task_cookie && !t2->core_task_cookie) {
+		/* CASE 2. */
+		sched_core_put_task_cookie(t1->core_task_cookie);
+		sched_core_put_after_stopper = true;
+
+		wr.tasks[0] = t1; /* Reset cookie for t1. */
+
+	} else if (!t1->core_task_cookie && t2->core_task_cookie) {
+		/* CASE 3. */
+		if (!sched_core_get_task_cookie(t2->core_task_cookie)) {
+			ret = -EINVAL;
+			goto out_unlock;
+		}
+
+		wr.tasks[0] = t1;
+		wr.cookies[0] = t2->core_task_cookie;
+
+	} else {
+		/* CASE 4. */
+		if (!sched_core_get_task_cookie(t2->core_task_cookie)) {
+			ret = -EINVAL;
+			goto out_unlock;
+		}
+		sched_core_put_task_cookie(t1->core_task_cookie);
+		sched_core_put_after_stopper = true;
+
+		wr.tasks[0] = t1;
+		wr.cookies[0] = t2->core_task_cookie;
+	}
+
+	stop_machine(sched_core_task_join_stopper, (void *)&wr, NULL);
+
+	if (sched_core_put_after_stopper)
+		sched_core_put();
+
+	ret = 0;
+out_unlock:
+	mutex_unlock(&sched_core_mutex);
+	return ret;
+}
+
+/* CGroup interface */
 static u64 cpu_core_tag_read_u64(struct cgroup_subsys_state *css, struct cftype *cft)
 {
 	struct task_group *tg = css_tg(css);
@@ -9207,18 +9435,9 @@ static int __sched_write_tag(void *data)
 	 * when we set cgroup tag to 0 when the loop is done below.
 	 */
 	while ((p = css_task_iter_next(&it))) {
-		p->core_cookie = !!val ? (unsigned long)tg : 0UL;
-
-		if (sched_core_enqueued(p)) {
-			sched_core_dequeue(task_rq(p), p);
-			if (!p->core_cookie)
-				continue;
-		}
-
-		if (sched_core_enabled(task_rq(p)) &&
-		    p->core_cookie && task_on_rq_queued(p))
-			sched_core_enqueue(task_rq(p), p);
+		unsigned long cookie = !!val ? (unsigned long)tg : 0UL;
 
+		sched_core_tag_requeue(p, cookie, true /* group */);
 	}
 	css_task_iter_end(&it);
 
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index c8fee8d9dfd4..88bf45267672 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -1024,6 +1024,10 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
 		__PS("clock-delta", t1-t0);
 	}
 
+#ifdef CONFIG_SCHED_CORE
+	__PS("core_cookie", p->core_cookie);
+#endif
+
 	sched_show_numa(p, m);
 }
 
-- 
2.29.0.rc1.297.gfa9743e501-goog