[PATCH] sched_ext: Fix scx_bpf_dsq_move_to_local___v2 compat detection

[PATCH] sched_ext: Fix scx_bpf_dsq_move_to_local___v2 compat detection

[Qiurong Fang]

From: fangqiurong <fangqiurong@kylinos.cn>

libbpf strips the last ___flavor suffix when resolving kfunc externs, so
the bare ___v2 declaration resolves to scx_bpf_dsq_move_to_local, whose
BTF proto lacks @enq_flags. The extern never matches, bpf_ksym_exists()
returns false on every kernel that has the ___v2 kfunc, and the macro
falls back to ___v1, silently dropping @enq_flags.

Add the trailing ___compat suffix used by the other versioned externs in
this file (scx_bpf_dsq_insert___v2, scx_bpf_reenqueue_local___v2).

scx_qmap passes needs_immed() as @enq_flags, so on time-shared cids the
SHARED_DSQ draining move currently drops SCX_ENQ_IMMED.

Fixes: e01a940b4813 ("sched_ext: Add enq_flags to scx_bpf_dsq_move_to_local()")
Assisted-by: Z.ai:glm-5.2
Signed-off-by: fangqiurong <fangqiurong@kylinos.cn>
---
 tools/sched_ext/include/scx/compat.bpf.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h
index cf469d5ff9ca..34eeb03afa2f 100644
--- a/tools/sched_ext/include/scx/compat.bpf.h
+++ b/tools/sched_ext/include/scx/compat.bpf.h
@@ -31,7 +31,7 @@ struct cgroup *scx_bpf_task_cgroup___new(struct task_struct *p) __ksym __weak;
  *
  * v7.1: scx_bpf_dsq_move_to_local___v2() to add @enq_flags.
  */
-bool scx_bpf_dsq_move_to_local___v2(u64 dsq_id, u64 enq_flags) __ksym __weak;
+bool scx_bpf_dsq_move_to_local___v2___compat(u64 dsq_id, u64 enq_flags) __ksym __weak;
 bool scx_bpf_dsq_move_to_local___v1(u64 dsq_id) __ksym __weak;
 void scx_bpf_dsq_move_set_slice___new(struct bpf_iter_scx_dsq *it__iter, u64 slice) __ksym __weak;
 void scx_bpf_dsq_move_set_vtime___new(struct bpf_iter_scx_dsq *it__iter, u64 vtime) __ksym __weak;
@@ -45,8 +45,8 @@ bool scx_bpf_dispatch_from_dsq___old(struct bpf_iter_scx_dsq *it__iter, struct t
 bool scx_bpf_dispatch_vtime_from_dsq___old(struct bpf_iter_scx_dsq *it__iter, struct task_struct *p, u64 dsq_id, u64 enq_flags) __ksym __weak;
 
 #define scx_bpf_dsq_move_to_local(dsq_id, enq_flags)				\
-	(bpf_ksym_exists(scx_bpf_dsq_move_to_local___v2) ?			\
-	 scx_bpf_dsq_move_to_local___v2((dsq_id), (enq_flags)) :		\
+	(bpf_ksym_exists(scx_bpf_dsq_move_to_local___v2___compat) ?		\
+	 scx_bpf_dsq_move_to_local___v2___compat((dsq_id), (enq_flags)) :	\
 	 (bpf_ksym_exists(scx_bpf_dsq_move_to_local___v1) ?			\
 	  scx_bpf_dsq_move_to_local___v1((dsq_id)) :				\
 	  scx_bpf_consume___old((dsq_id))))
-- 
2.43.0

Re: [PATCH] sched_ext: Fix scx_bpf_dsq_move_to_local___v2 compat detection

[Tejun Heo]

Applied to sched_ext/for-7.2-fixes with the following changes:

- Fixes: tag updated to point at 860683763ebf ("sched_ext: Add enq_flags
  to scx_bpf_dsq_move_to_local()"), the commit that's actually upstream.
  e01a940b4813 doesn't exist in the published tree.

- Cc: stable@vger.kernel.org # v7.1+ added.

- The scx_qmap paragraph replaced with a generic impact statement as
  needs_immed() doesn't exist in the applied branch.

Thanks.

--
tejun