[PATCH v2] sched/core: Fix reset-on-fork from RT with uclamp

[PATCH v2] sched/core: Fix reset-on-fork from RT with uclamp

[Quentin Perret]

uclamp_fork() resets the uclamp values to their default when the
reset-on-fork flag is set. It also checks whether the task has a RT
policy, and sets its uclamp.min to 1024 accordingly. However, during
reset-on-fork, the task's policy is lowered to SCHED_NORMAL right after,
hence leading to an erroneous uclamp.min setting for the new task if it
was forked from RT.

Fix this by removing the unnecessary check on rt_task() in
uclamp_fork() as this doesn't make sense if the reset-on-fork flag is
set.

Fixes: 1a00d999971c ("sched/uclamp: Set default clamps for RT tasks")
Reported-by: Chitti Babu Theegala <ctheegal@codeaurora.org>
Reviewed-by: Patrick Bellasi <patrick.bellasi@matbug.net>
Signed-off-by: Quentin Perret <qperret@google.com>
---
Changes in v2:
 - Added missing 'Fixes:' tag (Patrick)
 - Removed unnecessary local variable (Doug, Patrick)
---
 kernel/sched/core.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3a61a3b8eaa9..9a2fbf98fd6f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1232,13 +1232,8 @@ static void uclamp_fork(struct task_struct *p)
 		return;
 
 	for_each_clamp_id(clamp_id) {
-		unsigned int clamp_value = uclamp_none(clamp_id);
-
-		/* By default, RT tasks always get 100% boost */
-		if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
-			clamp_value = uclamp_none(UCLAMP_MAX);
-
-		uclamp_se_set(&p->uclamp_req[clamp_id], clamp_value, false);
+		uclamp_se_set(&p->uclamp_req[clamp_id],
+			      uclamp_none(clamp_id), false);
 	}
 }
 
-- 
2.26.1.301.g55bc3eb7cb9-goog

Re: [PATCH v2] sched/core: Fix reset-on-fork from RT with uclamp

[Dietmar Eggemann]

On 16.04.20 10:59, Quentin Perret wrote:
> uclamp_fork() resets the uclamp values to their default when the
> reset-on-fork flag is set. It also checks whether the task has a RT
> policy, and sets its uclamp.min to 1024 accordingly. However, during
> reset-on-fork, the task's policy is lowered to SCHED_NORMAL right after,
> hence leading to an erroneous uclamp.min setting for the new task if it
> was forked from RT.
> 
> Fix this by removing the unnecessary check on rt_task() in
> uclamp_fork() as this doesn't make sense if the reset-on-fork flag is
> set.
> 
> Fixes: 1a00d999971c ("sched/uclamp: Set default clamps for RT tasks")
> Reported-by: Chitti Babu Theegala <ctheegal@codeaurora.org>
> Reviewed-by: Patrick Bellasi <patrick.bellasi@matbug.net>
> Signed-off-by: Quentin Perret <qperret@google.com>
> ---
> Changes in v2:
>  - Added missing 'Fixes:' tag (Patrick)
>  - Removed unnecessary local variable (Doug, Patrick)
> ---
>  kernel/sched/core.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 3a61a3b8eaa9..9a2fbf98fd6f 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1232,13 +1232,8 @@ static void uclamp_fork(struct task_struct *p)
>  		return;
>  
>  	for_each_clamp_id(clamp_id) {
> -		unsigned int clamp_value = uclamp_none(clamp_id);
> -
> -		/* By default, RT tasks always get 100% boost */
> -		if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
> -			clamp_value = uclamp_none(UCLAMP_MAX);
> -
> -		uclamp_se_set(&p->uclamp_req[clamp_id], clamp_value, false);
> +		uclamp_se_set(&p->uclamp_req[clamp_id],
> +			      uclamp_none(clamp_id), false);
>  	}
>  }

LGTM.

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

Re: [PATCH v2] sched/core: Fix reset-on-fork from RT with uclamp

[Peter Zijlstra]

On Thu, Apr 16, 2020 at 01:03:16PM +0200, Dietmar Eggemann wrote:
> On 16.04.20 10:59, Quentin Perret wrote:
> > uclamp_fork() resets the uclamp values to their default when the
> > reset-on-fork flag is set. It also checks whether the task has a RT
> > policy, and sets its uclamp.min to 1024 accordingly. However, during
> > reset-on-fork, the task's policy is lowered to SCHED_NORMAL right after,
> > hence leading to an erroneous uclamp.min setting for the new task if it
> > was forked from RT.
> > 
> > Fix this by removing the unnecessary check on rt_task() in
> > uclamp_fork() as this doesn't make sense if the reset-on-fork flag is
> > set.
> > 
> > Fixes: 1a00d999971c ("sched/uclamp: Set default clamps for RT tasks")
> > Reported-by: Chitti Babu Theegala <ctheegal@codeaurora.org>
> > Reviewed-by: Patrick Bellasi <patrick.bellasi@matbug.net>
> > Signed-off-by: Quentin Perret <qperret@google.com>
> > ---
> > Changes in v2:
> >  - Added missing 'Fixes:' tag (Patrick)
> >  - Removed unnecessary local variable (Doug, Patrick)
> > ---
> >  kernel/sched/core.c | 9 ++-------
> >  1 file changed, 2 insertions(+), 7 deletions(-)
> > 
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 3a61a3b8eaa9..9a2fbf98fd6f 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1232,13 +1232,8 @@ static void uclamp_fork(struct task_struct *p)
> >  		return;
> >  
> >  	for_each_clamp_id(clamp_id) {
> > -		unsigned int clamp_value = uclamp_none(clamp_id);
> > -
> > -		/* By default, RT tasks always get 100% boost */
> > -		if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
> > -			clamp_value = uclamp_none(UCLAMP_MAX);
> > -
> > -		uclamp_se_set(&p->uclamp_req[clamp_id], clamp_value, false);
> > +		uclamp_se_set(&p->uclamp_req[clamp_id],
> > +			      uclamp_none(clamp_id), false);
> >  	}
> >  }
> 
> LGTM.
> 
> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

Thanks guys!

[tip: sched/urgent] sched/core: Fix reset-on-fork from RT with uclamp

[tip-bot2 for Quentin Perret]

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

Commit-ID:     eaf5a92ebde5bca3bb2565616115bd6d579486cd
Gitweb:        https://git.kernel.org/tip/eaf5a92ebde5bca3bb2565616115bd6d579486cd
Author:        Quentin Perret <qperret@google.com>
AuthorDate:    Thu, 16 Apr 2020 09:59:56 +01:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 22 Apr 2020 23:10:13 +02:00

sched/core: Fix reset-on-fork from RT with uclamp

uclamp_fork() resets the uclamp values to their default when the
reset-on-fork flag is set. It also checks whether the task has a RT
policy, and sets its uclamp.min to 1024 accordingly. However, during
reset-on-fork, the task's policy is lowered to SCHED_NORMAL right after,
hence leading to an erroneous uclamp.min setting for the new task if it
was forked from RT.

Fix this by removing the unnecessary check on rt_task() in
uclamp_fork() as this doesn't make sense if the reset-on-fork flag is
set.

Fixes: 1a00d999971c ("sched/uclamp: Set default clamps for RT tasks")
Reported-by: Chitti Babu Theegala <ctheegal@codeaurora.org>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Patrick Bellasi <patrick.bellasi@matbug.net>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lkml.kernel.org/r/20200416085956.217587-1-qperret@google.com
---
 kernel/sched/core.c |  9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3a61a3b..9a2fbf9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1232,13 +1232,8 @@ static void uclamp_fork(struct task_struct *p)
 		return;
 
 	for_each_clamp_id(clamp_id) {
-		unsigned int clamp_value = uclamp_none(clamp_id);
-
-		/* By default, RT tasks always get 100% boost */
-		if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
-			clamp_value = uclamp_none(UCLAMP_MAX);
-
-		uclamp_se_set(&p->uclamp_req[clamp_id], clamp_value, false);
+		uclamp_se_set(&p->uclamp_req[clamp_id],
+			      uclamp_none(clamp_id), false);
 	}
 }