2023-02-06 22:34:20

by Pietro Borrello

Subject: [PATCH v3] sched: pick_next_rt_entity(): check list_entry

Commit 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
removed any path which could make pick_next_rt_entity() return NULL.
However, BUG_ON(!rt_se) in _pick_next_task_rt() (the only caller of
pick_next_rt_entity()) still checks the error condition, which can
never happen, since list_entry() never returns NULL.
Remove the BUG_ON check, and instead emit a warning in the only
possible error condition here: the queue being empty which should
never happen.

Fixes: 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
Signed-off-by: Pietro Borrello <[email protected]>
---
Changes in v3:
- return NULL if the list is empty
- Link to v2: https://lore.kernel.org/r/20230128-list-entry-null-check-sched-v2-1-d8e010cce91b@diag.uniroma1.it

Changes in v2:
- pick_next_rt_entity(): emit warning instead of crashing
- Link to v1: https://lore.kernel.org/r/20230128-list-entry-null-check-sched-v1-1-c93085ee0055@diag.uniroma1.it
---
kernel/sched/rt.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index ed2a47e4ddae..0a11f44adee5 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1777,6 +1777,8 @@ static struct sched_rt_entity *pick_next_rt_entity(struct rt_rq *rt_rq)
BUG_ON(idx >= MAX_RT_PRIO);

queue = array->queue + idx;
+ if (SCHED_WARN_ON(list_empty(queue)))
+ return NULL;
next = list_entry(queue->next, struct sched_rt_entity, run_list);

return next;
@@ -1789,7 +1791,8 @@ static struct task_struct *_pick_next_task_rt(struct rq *rq)

do {
rt_se = pick_next_rt_entity(rt_rq);
- BUG_ON(!rt_se);
+ if (unlikely(!rt_se))
+ return NULL;
rt_rq = group_rt_rq(rt_se);
} while (rt_rq);


---
base-commit: 2241ab53cbb5cdb08a6b2d4688feb13971058f65
change-id: 20230128-list-entry-null-check-sched-a3f3dfd6d468

Best regards,
--
Pietro Borrello <[email protected]>

2023-02-07 12:30:44

by Phil Auld

Subject: Re: [PATCH v3] sched: pick_next_rt_entity(): check list_entry

Hi Pietro,

On Mon, Feb 06, 2023 at 10:33:54PM +0000 Pietro Borrello wrote:
> Commit 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
> removed any path which could make pick_next_rt_entity() return NULL.
> However, BUG_ON(!rt_se) in _pick_next_task_rt() (the only caller of
> pick_next_rt_entity()) still checks the error condition, which can
> never happen, since list_entry() never returns NULL.
> Remove the BUG_ON check, and instead emit a warning in the only
> possible error condition here: the queue being empty which should
> never happen.
>
> Fixes: 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
> Signed-off-by: Pietro Borrello <[email protected]>
> ---
> Changes in v3:
> - return NULL if the list is empty
> - Link to v2: https://lore.kernel.org/r/20230128-list-entry-null-check-sched-v2-1-d8e010cce91b@diag.uniroma1.it
>
> Changes in v2:
> - pick_next_rt_entity(): emit warning instead of crashing
> - Link to v1: https://lore.kernel.org/r/20230128-list-entry-null-check-sched-v1-1-c93085ee0055@diag.uniroma1.it
> ---
> kernel/sched/rt.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index ed2a47e4ddae..0a11f44adee5 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1777,6 +1777,8 @@ static struct sched_rt_entity *pick_next_rt_entity(struct rt_rq *rt_rq)
> BUG_ON(idx >= MAX_RT_PRIO);
>
> queue = array->queue + idx;
> + if (SCHED_WARN_ON(list_empty(queue)))
> + return NULL;
> next = list_entry(queue->next, struct sched_rt_entity, run_list);
>
> return next;
> @@ -1789,7 +1791,8 @@ static struct task_struct *_pick_next_task_rt(struct rq *rq)
>
> do {
> rt_se = pick_next_rt_entity(rt_rq);
> - BUG_ON(!rt_se);
> + if (unlikely(!rt_se))
> + return NULL;
> rt_rq = group_rt_rq(rt_se);
> } while (rt_rq);
>
>
> ---
> base-commit: 2241ab53cbb5cdb08a6b2d4688feb13971058f65
> change-id: 20230128-list-entry-null-check-sched-a3f3dfd6d468
>
> Best regards,
> --
> Pietro Borrello <[email protected]>
>


Reviewed-by: Phil Auld <[email protected]>

Thanks. I think this will be useful.


Cheers,
Phil


--

2023-02-07 15:12:00

by Steven Rostedt

Subject: Re: [PATCH v3] sched: pick_next_rt_entity(): check list_entry

On Mon, 06 Feb 2023 22:33:54 +0000
Pietro Borrello <[email protected]> wrote:

> Commit 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
> removed any path which could make pick_next_rt_entity() return NULL.
> However, BUG_ON(!rt_se) in _pick_next_task_rt() (the only caller of
> pick_next_rt_entity()) still checks the error condition, which can
> never happen, since list_entry() never returns NULL.
> Remove the BUG_ON check, and instead emit a warning in the only
> possible error condition here: the queue being empty which should
> never happen.
>
> Fixes: 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
> Signed-off-by: Pietro Borrello <[email protected]>
> ---
> Changes in v3:
> - return NULL if the list is empty
> - Link to v2: https://lore.kernel.org/r/20230128-list-entry-null-check-sched-v2-1-d8e010cce91b@diag.uniroma1.it
>
> Changes in v2:
> - pick_next_rt_entity(): emit warning instead of crashing
> - Link to v1: https://lore.kernel.org/r/20230128-list-entry-null-check-sched-v1-1-c93085ee0055@diag.uniroma1.it
> ---
> kernel/sched/rt.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index ed2a47e4ddae..0a11f44adee5 100644

Reviewed-by: Steven Rostedt (Google) <[email protected]>

-- Steve

2023-02-11 10:31:06

by tip-bot2 for Alexey Makhalov

Subject: [tip: sched/core] sched/rt: pick_next_rt_entity(): check list_entry

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

Commit-ID: 7c4a5b89a0b5a57a64b601775b296abf77a9fe97
Gitweb: https://git.kernel.org/tip/7c4a5b89a0b5a57a64b601775b296abf77a9fe97
Author: Pietro Borrello <[email protected]>
AuthorDate: Mon, 06 Feb 2023 22:33:54
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Sat, 11 Feb 2023 11:18:10 +01:00

sched/rt: pick_next_rt_entity(): check list_entry

Commit 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
removed any path which could make pick_next_rt_entity() return NULL.
However, BUG_ON(!rt_se) in _pick_next_task_rt() (the only caller of
pick_next_rt_entity()) still checks the error condition, which can
never happen, since list_entry() never returns NULL.
Remove the BUG_ON check, and instead emit a warning in the only
possible error condition here: the queue being empty which should
never happen.

Fixes: 326587b84078 ("sched: fix goto retry in pick_next_task_rt()")
Signed-off-by: Pietro Borrello <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Phil Auld <[email protected]>
Reviewed-by: Steven Rostedt (Google) <[email protected]>
Link: https://lore.kernel.org/r/20230128-list-entry-null-check-sched-v3-1-b1a71bd1ac6b@diag.uniroma1.it
---
kernel/sched/rt.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index ed2a47e..0a11f44 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1777,6 +1777,8 @@ static struct sched_rt_entity *pick_next_rt_entity(struct rt_rq *rt_rq)
BUG_ON(idx >= MAX_RT_PRIO);

queue = array->queue + idx;
+ if (SCHED_WARN_ON(list_empty(queue)))
+ return NULL;
next = list_entry(queue->next, struct sched_rt_entity, run_list);

return next;
@@ -1789,7 +1791,8 @@ static struct task_struct *_pick_next_task_rt(struct rq *rq)

do {
rt_se = pick_next_rt_entity(rt_rq);
- BUG_ON(!rt_se);
+ if (unlikely(!rt_se))
+ return NULL;
rt_rq = group_rt_rq(rt_se);
} while (rt_rq);

2023-03-04 10:18:26

by guanjing (D)

Subject: Re: [PATCH v3] sched: pick_next_rt_entity(): check list_entry

Hi, borrello:

I wonder why you send this patch? Did you meet such a problem in a
real-world scenario, or it is a static warning style?

Thanks,
Guanjin.