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[PATCH 1/8] sched: Fix hrtick() vs scheduling context

Peter Zijlstra posted 8 patches 4 months, 3 weeks ago
There is a newer version of this series
[PATCH 1/8] sched: Fix hrtick() vs scheduling context
Posted by Peter Zijlstra 4 months, 3 weeks ago 
The sched_class::task_tick() method is called on the donor
sched_class, and sched_tick() hands it rq->donor as argument, which is
consistent.

However, while hrtick() uses the donor sched_class, it then passes
rq->curr, which is inconsistent. Fix it.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/core.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -875,7 +875,7 @@ static enum hrtimer_restart hrtick(struc
 
 	rq_lock(rq, &rf);
 	update_rq_clock(rq);
-	rq->donor->sched_class->task_tick(rq, rq->curr, 1);
+	rq->donor->sched_class->task_tick(rq, rq->donor, 1);
 	rq_unlock(rq, &rf);
 
 	return HRTIMER_NORESTART;
Re: [PATCH 1/8] sched: Fix hrtick() vs scheduling context
Posted by John Stultz 4 months, 2 weeks ago 
On Thu, Sep 18, 2025 at 1:06 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> The sched_class::task_tick() method is called on the donor
> sched_class, and sched_tick() hands it rq->donor as argument, which is
> consistent.
>
> However, while hrtick() uses the donor sched_class, it then passes
> rq->curr, which is inconsistent. Fix it.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  kernel/sched/core.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -875,7 +875,7 @@ static enum hrtimer_restart hrtick(struc
>
>         rq_lock(rq, &rf);
>         update_rq_clock(rq);
> -       rq->donor->sched_class->task_tick(rq, rq->curr, 1);
> +       rq->donor->sched_class->task_tick(rq, rq->donor, 1);
>         rq_unlock(rq, &rf);

Ah. Thanks for catching this! I've run through with some stress
testing on this and haven't seen any problems so far.

Acked-by: John Stultz <jstultz@google.com>

thanks
-john
Re: [PATCH 1/8] sched: Fix hrtick() vs scheduling context
Posted by K Prateek Nayak 4 months, 3 weeks ago 
Hello Peter,

On 9/18/2025 1:22 PM, Peter Zijlstra wrote:
> The sched_class::task_tick() method is called on the donor
> sched_class, and sched_tick() hands it rq->donor as argument, which is
> consistent.
> 
> However, while hrtick() uses the donor sched_class, it then passes
> rq->curr, which is inconsistent. Fix it.

Can we add either a:

Fixes: 7de9d4f94638 ("sched: Start blocked_on chain processing in find_proxy_task()")

where this starts making a difference functionally since single CPU
proxy can have rq->curr != rq->donor, or we can target the same commit
where task_tick(0 in sched_tick() was updated with:

Fixes: af0c8b2bf67b ("sched: Split scheduler and execution contexts")

Other than that, this looks good to me. Feel free to include:

Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>

> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  kernel/sched/core.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -875,7 +875,7 @@ static enum hrtimer_restart hrtick(struc
>  
>  	rq_lock(rq, &rf);
>  	update_rq_clock(rq);
> -	rq->donor->sched_class->task_tick(rq, rq->curr, 1);
> +	rq->donor->sched_class->task_tick(rq, rq->donor, 1);
>  	rq_unlock(rq, &rf);
>  
>  	return HRTIMER_NORESTART;
> 
> 
> 

-- 
Thanks and Regards,
Prateek
[tip: sched/urgent] sched/hrtick: Fix hrtick() vs. scheduling context
Posted by tip-bot2 for Peter Zijlstra 2 months ago 
The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     e38e5299747b23015b00b0109891815db44a2f30
Gitweb:        https://git.kernel.org/tip/e38e5299747b23015b00b0109891815db44a2f30
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Mon, 01 Sep 2025 22:46:29 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Sat, 06 Dec 2025 10:03:13 +01:00

sched/hrtick: Fix hrtick() vs. scheduling context

The sched_class::task_tick() method is called on the donor
sched_class, and sched_tick() hands it rq->donor as argument,
which is consistent.

However, while hrtick() uses the donor sched_class, it then passes
rq->curr, which is inconsistent. Fix it.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: John Stultz <jstultz@google.com>
Link: https://patch.msgid.link/20250918080205.442967033@infradead.org
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fc358c1..1711e9e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -878,7 +878,7 @@ static enum hrtimer_restart hrtick(struct hrtimer *timer)
 
 	rq_lock(rq, &rf);
 	update_rq_clock(rq);
-	rq->donor->sched_class->task_tick(rq, rq->curr, 1);
+	rq->donor->sched_class->task_tick(rq, rq->donor, 1);
 	rq_unlock(rq, &rf);
 
 	return HRTIMER_NORESTART;
[tip: sched/urgent] sched/hrtick: Fix hrtick() vs. scheduling context
Posted by tip-bot2 for Peter Zijlstra 2 months, 1 week ago 
The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     40671f3f91986844df8947b65b9af5e770752047
Gitweb:        https://git.kernel.org/tip/40671f3f91986844df8947b65b9af5e770752047
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Mon, 01 Sep 2025 22:46:29 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 03 Dec 2025 19:26:00 +01:00

sched/hrtick: Fix hrtick() vs. scheduling context

The sched_class::task_tick() method is called on the donor
sched_class, and sched_tick() hands it rq->donor as argument,
which is consistent.

However, while hrtick() uses the donor sched_class, it then passes
rq->curr, which is inconsistent. Fix it.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: John Stultz <jstultz@google.com>
Link: https://patch.msgid.link/20250918080205.442967033@infradead.org
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fc358c1..1711e9e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -878,7 +878,7 @@ static enum hrtimer_restart hrtick(struct hrtimer *timer)
 
 	rq_lock(rq, &rf);
 	update_rq_clock(rq);
-	rq->donor->sched_class->task_tick(rq, rq->curr, 1);
+	rq->donor->sched_class->task_tick(rq, rq->donor, 1);
 	rq_unlock(rq, &rf);
 
 	return HRTIMER_NORESTART;
[tip: sched/urgent] sched/hrtick: Fix hrtick() vs. scheduling context
Posted by tip-bot2 for Peter Zijlstra 2 months, 1 week ago 
The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     8720ba2d028f1aff08a55d8fe1a124dd5a6cfb0a
Gitweb:        https://git.kernel.org/tip/8720ba2d028f1aff08a55d8fe1a124dd5a6cfb0a
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Mon, 01 Sep 2025 22:46:29 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 02 Dec 2025 15:37:52 +01:00

sched/hrtick: Fix hrtick() vs. scheduling context

The sched_class::task_tick() method is called on the donor
sched_class, and sched_tick() hands it rq->donor as argument,
which is consistent.

However, while hrtick() uses the donor sched_class, it then passes
rq->curr, which is inconsistent. Fix it.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: John Stultz <jstultz@google.com>
Link: https://patch.msgid.link/20250918080205.442967033@infradead.org
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7dfb6a9..be55f95 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -878,7 +878,7 @@ static enum hrtimer_restart hrtick(struct hrtimer *timer)
 
 	rq_lock(rq, &rf);
 	update_rq_clock(rq);
-	rq->donor->sched_class->task_tick(rq, rq->curr, 1);
+	rq->donor->sched_class->task_tick(rq, rq->donor, 1);
 	rq_unlock(rq, &rf);
 
 	return HRTIMER_NORESTART;

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