[PATCH v2] sched_ext: Avoid flooding the log with deprecation warnings

[Breno Leitao <leitao@debian.org>]

The deprecation notices for direct p->scx.slice/dsq_vtime writes and for
ops->cpu_acquire/release() use plain pr_warn(), so they repeat on every
scheduler (re)load and can flood the kernel log.

The slice/dsq_vtime notice is the worst offender: it is emitted from the
BPF verifier's btf_struct_access callback, which is re-evaluated as the
verifier explores program paths, so a single scheduler load can print it
many times -- hundreds of lines on some hosts, dozens within the same
second.

Switch both notices to pr_warn_ratelimited() so each deprecation is still
reported but bursts no longer spam the log, and add the missing newline
to the slice/dsq_vtime message.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
Changes in v2:
- Switch both deprecation notices from pr_warn_once() to
  pr_warn_ratelimited() (Christian, Andrea)
- Link to v1: https://lore.kernel.org/r/20260623-scx_warning-v1-1-14bf218f4bd9@debian.org
---
 kernel/sched/ext/ext.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index 691d53fe0f648..d62b93f48a854 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -6988,7 +6988,7 @@ static int validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops)
 	 * run past the BPF allocation. Skip for cid-form.
 	 */
 	if (!sch->is_cid_type && (ops->cpu_acquire || ops->cpu_release))
-		pr_warn("ops->cpu_acquire/release() are deprecated, use sched_switch TP instead\n");
+		pr_warn_ratelimited("ops->cpu_acquire/release() are deprecated, use sched_switch TP instead\n");
 
 	/*
 	 * Sub-scheduler support is tied to the cid-form struct_ops. A sub-sched
@@ -7806,7 +7806,7 @@ static int bpf_scx_btf_struct_access(struct bpf_verifier_log *log,
 		     off + size <= offsetofend(struct task_struct, scx.slice)) ||
 		    (off >= offsetof(struct task_struct, scx.dsq_vtime) &&
 		     off + size <= offsetofend(struct task_struct, scx.dsq_vtime))) {
-			pr_warn("sched_ext: Writing directly to p->scx.slice/dsq_vtime is deprecated, use scx_bpf_task_set_slice/dsq_vtime()");
+			pr_warn_ratelimited("sched_ext: Writing directly to p->scx.slice/dsq_vtime is deprecated, use scx_bpf_task_set_slice/dsq_vtime()\n");
 			return SCALAR_VALUE;
 		}
 

---
base-commit: 4e5dfb7c84012007c3c7061126491bbc92d71bf1
change-id: 20260623-scx_warning-0df49c442afb

Best regards,
-- 
Breno Leitao <leitao@debian.org>