Commit 2dbbdeda authored by Tejun Heo's avatar Tejun Heo
Browse files

sched_ext: Fix scx_bpf_dsq_insert() backward binary compatibility 



cded46d9 ("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: cded46d9 ("sched_ext: Make scx_bpf_dsq_insert*() return bool")
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 67fa319f

kernel/sched/ext.c

+6 −6
Original line number Diff line number Diff line
@@ -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)

tools/sched_ext/include/scx/compat.bpf.h

+5 −5
Original line number Diff line number Diff line
@@ -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;

	}

}