2020-04-16 09:03:50

by Quentin Perret

Subject: [PATCH v2] 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 <[email protected]>
Reviewed-by: Patrick Bellasi <[email protected]>
Signed-off-by: Quentin Perret <[email protected]>
---
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

2020-04-16 17:18:10

by Dietmar Eggemann

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

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 <[email protected]>
> Reviewed-by: Patrick Bellasi <[email protected]>
> Signed-off-by: Quentin Perret <[email protected]>
> ---
> 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 <[email protected]>

2020-04-16 17:25:28

by Peter Zijlstra

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

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 <[email protected]>
> > Reviewed-by: Patrick Bellasi <[email protected]>
> > Signed-off-by: Quentin Perret <[email protected]>
> > ---
> > 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 <[email protected]>

Thanks guys!

2020-04-22 21:22:12

by tip-bot2 for Alexey Makhalov

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

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 <[email protected]>
AuthorDate: Thu, 16 Apr 2020 09:59:56 +01:00
Committer: Peter Zijlstra <[email protected]>
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 <[email protected]>
Signed-off-by: Quentin Perret <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Patrick Bellasi <[email protected]>
Reviewed-by: Dietmar Eggemann <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
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);
}
}