sched_ext: Fix scx_bpf_dsq_insert() backward binary compatibility

cded46d97159 ("sched_ext: Make scx_bpf_dsq_insert*() return bool")
introduced a new bool-returning scx_bpf_dsq_insert() and renamed the old
void-returning version to scx_bpf_dsq_insert___compat, with the expectation
that libbpf would match old binaries to the ___compat variant, maintaining
backward binary compatibility. However, while libbpf ignores ___suffix on
the BPF side when matching symbols, it doesn't do so for kernel-side symbols.
Old binaries compiled with the original scx_bpf_dsq_insert() could no longer
resolve the symbol.

Fix by reversing the naming: Keep scx_bpf_dsq_insert() as the old
void-returning interface and add ___v2 to the new bool-returning version.
This allows old binaries to continue working while new code can use the
___v2 variant. Once libbpf is updated to ignore kernel-side ___SUFFIX, the
___v2 suffix can be dropped when the compat interface is removed.

v2: Use ___v2 instead of ___new.

Fixes: cded46d97159 ("sched_ext: Make scx_bpf_dsq_insert*() return bool")
Signed-off-by: Tejun Heo <tj@kernel.org>

2 files changed, 11 insertions, 11 deletions

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 35bc37c7ee19..dc86ce0be32a 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -5421,8 +5421,8 @@ __bpf_kfunc_start_defs();
  * scheduler, %false return triggers scheduler abort and the caller doesn't need
  * to check the return value.
  */
-__bpf_kfunc bool scx_bpf_dsq_insert(struct task_struct *p, u64 dsq_id, u64 slice,
-				    u64 enq_flags)
+__bpf_kfunc bool scx_bpf_dsq_insert___v2(struct task_struct *p, u64 dsq_id,
+					 u64 slice, u64 enq_flags)
 {
 	struct scx_sched *sch;
 
@@ -5445,12 +5445,12 @@ __bpf_kfunc bool scx_bpf_dsq_insert(struct task_struct *p, u64 dsq_id, u64 slice
 }
 
 /*
- * COMPAT: Will be removed in v6.23.
+ * COMPAT: Will be removed in v6.23 along with the ___v2 suffix.
  */
-__bpf_kfunc void scx_bpf_dsq_insert___compat(struct task_struct *p, u64 dsq_id,
+__bpf_kfunc void scx_bpf_dsq_insert(struct task_struct *p, u64 dsq_id,
 					     u64 slice, u64 enq_flags)
 {
-	scx_bpf_dsq_insert(p, dsq_id, slice, enq_flags);
+	scx_bpf_dsq_insert___v2(p, dsq_id, slice, enq_flags);
 }
 
 static bool scx_dsq_insert_vtime(struct scx_sched *sch, struct task_struct *p,
@@ -5546,7 +5546,7 @@ __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(scx_kfunc_ids_enqueue_dispatch)
 BTF_ID_FLAGS(func, scx_bpf_dsq_insert, KF_RCU)
-BTF_ID_FLAGS(func, scx_bpf_dsq_insert___compat, KF_RCU)
+BTF_ID_FLAGS(func, scx_bpf_dsq_insert___v2, KF_RCU)
 BTF_ID_FLAGS(func, __scx_bpf_dsq_insert_vtime, KF_RCU)
 BTF_ID_FLAGS(func, scx_bpf_dsq_insert_vtime, KF_RCU)
 BTF_KFUNCS_END(scx_kfunc_ids_enqueue_dispatch)
diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h
index 619a16f0d39a..a023b71991a6 100644
--- a/tools/sched_ext/include/scx/compat.bpf.h
+++ b/tools/sched_ext/include/scx/compat.bpf.h
@@ -238,16 +238,16 @@ scx_bpf_dsq_insert_vtime(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime
  * v6.19: scx_bpf_dsq_insert() now returns bool instead of void. Move
  * scx_bpf_dsq_insert() decl to common.bpf.h and drop compat helper after v6.22.
  */
-bool scx_bpf_dsq_insert___new(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags) __ksym __weak;
-void scx_bpf_dsq_insert___compat(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags) __ksym __weak;
+bool scx_bpf_dsq_insert___v2(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags) __ksym __weak;
+void scx_bpf_dsq_insert___v1(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags) __ksym __weak;
 
 static inline bool
 scx_bpf_dsq_insert(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags)
 {
-	if (bpf_ksym_exists(scx_bpf_dsq_insert___new)) {
-		return scx_bpf_dsq_insert___new(p, dsq_id, slice, enq_flags);
+	if (bpf_ksym_exists(scx_bpf_dsq_insert___v2)) {
+		return scx_bpf_dsq_insert___v2(p, dsq_id, slice, enq_flags);
 	} else {
-		scx_bpf_dsq_insert___compat(p, dsq_id, slice, enq_flags);
+		scx_bpf_dsq_insert___v1(p, dsq_id, slice, enq_flags);
 		return true;
 	}
 }