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Message-ID: <CABFh=a4Vn+FCe9DTLt_p7RzNBSJFU-he+OhNqTK_Z3C5NbP7KA@mail.gmail.com>
Date: Wed, 22 Oct 2025 10:44:02 -0400
From: Emil Tsalapatis <emil@...alapatis.com>
To: Andrea Righi <arighi@...dia.com>
Cc: Tejun Heo <tj@...nel.org>, David Vernet <void@...ifault.com>,
Changwoo Min <changwoo@...lia.com>, sched-ext@...ts.linux.dev,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH sched_ext/for-6.19] sched_ext: Use ___v2 suffix for new
kfuncs and fix scx build errors
Hi Andrea,
On Wed, Oct 22, 2025 at 5:38 AM Andrea Righi <arighi@...dia.com> wrote:
>
> Following commit 2dbbdeda77a61 ("sched_ext: Fix scx_bpf_dsq_insert()
> backward binary compatibility"), consistently use the ___v2 suffix also
> to the new scx_bpf_dsq_insert_vtime() and scx_bpf_select_cpu_and()
> kfuncs.
>
> Introduce __COMPAT_scx_bpf_select_cpu_and() and
> __COMPAT_scx_bpf_dsq_insert_vtime(), to ensure schedulers can transition
> smoothly to the updated interfaces, and temporarily mirror the
> definitions of struct scx_bpf_select_cpu_and_args and struct
> scx_bpf_dsq_insert_vtime_args to prevent build failures on kernels where
> these structs are not yet defined.
>
> Both the compatibility helpers and mirrored structs will be removed in
> v6.23.
>
> With these changes in place, all schedulers in the scx repository build
> and run correctly with the updated headers.
>
> Fixes: c0d630ba347c7 ("sched_ext: Wrap kfunc args in struct to prepare for aux__prog")
> Signed-off-by: Andrea Righi <arighi@...dia.com>
> ---
> kernel/sched/ext.c | 10 ++--
> kernel/sched/ext_idle.c | 10 ++--
> tools/sched_ext/include/scx/common.bpf.h | 3 --
> tools/sched_ext/include/scx/compat.bpf.h | 63 +++++++++++++++++-------
> 4 files changed, 56 insertions(+), 30 deletions(-)
>
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index cb41365032ebc..8816d89426a6f 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -5490,7 +5490,7 @@ struct scx_bpf_dsq_insert_vtime_args {
> };
>
> /**
> - * __scx_bpf_dsq_insert_vtime - Arg-wrapped vtime DSQ insertion
> + * scx_bpf_dsq_insert_vtime___v2 - Arg-wrapped vtime DSQ insertion
> * @p: task_struct to insert
> * @args: struct containing the rest of the arguments
> * @args->dsq_id: DSQ to insert into
> @@ -5520,8 +5520,8 @@ struct scx_bpf_dsq_insert_vtime_args {
> * to check the return value.
> */
> __bpf_kfunc bool
> -__scx_bpf_dsq_insert_vtime(struct task_struct *p,
> - struct scx_bpf_dsq_insert_vtime_args *args)
> +scx_bpf_dsq_insert_vtime___v2(struct task_struct *p,
> + struct scx_bpf_dsq_insert_vtime_args *args)
> {
> struct scx_sched *sch;
>
> @@ -5536,7 +5536,7 @@ __scx_bpf_dsq_insert_vtime(struct task_struct *p,
> }
>
> /*
> - * 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_vtime(struct task_struct *p, u64 dsq_id,
> u64 slice, u64 vtime, u64 enq_flags)
> @@ -5557,7 +5557,7 @@ __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___v2, KF_RCU)
> -BTF_ID_FLAGS(func, __scx_bpf_dsq_insert_vtime, KF_RCU)
> +BTF_ID_FLAGS(func, scx_bpf_dsq_insert_vtime___v2, KF_RCU)
> BTF_ID_FLAGS(func, scx_bpf_dsq_insert_vtime, KF_RCU)
> BTF_KFUNCS_END(scx_kfunc_ids_enqueue_dispatch)
>
> diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
> index 3d9d404d5cd20..d4b6b5a300345 100644
> --- a/kernel/sched/ext_idle.c
> +++ b/kernel/sched/ext_idle.c
> @@ -1003,7 +1003,7 @@ struct scx_bpf_select_cpu_and_args {
> };
>
> /**
> - * __scx_bpf_select_cpu_and - Arg-wrapped CPU selection with cpumask
> + * scx_bpf_select_cpu_and___v2 - Arg-wrapped CPU selection with cpumask
> * @p: task_struct to select a CPU for
> * @cpus_allowed: cpumask of allowed CPUs
> * @args: struct containing the rest of the arguments
> @@ -1027,8 +1027,8 @@ struct scx_bpf_select_cpu_and_args {
> * a negative value if no idle CPU is available.
> */
> __bpf_kfunc s32
> -__scx_bpf_select_cpu_and(struct task_struct *p, const struct cpumask *cpus_allowed,
> - struct scx_bpf_select_cpu_and_args *args)
> +scx_bpf_select_cpu_and___v2(struct task_struct *p, const struct cpumask *cpus_allowed,
> + struct scx_bpf_select_cpu_and_args *args)
> {
> struct scx_sched *sch;
>
> @@ -1043,7 +1043,7 @@ __scx_bpf_select_cpu_and(struct task_struct *p, const struct cpumask *cpus_allow
> }
>
> /*
> - * COMPAT: Will be removed in v6.22.
> + * COMPAT: Will be removed in v6.22 along with the ___v2 suffix.
> */
> __bpf_kfunc s32 scx_bpf_select_cpu_and(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
> const struct cpumask *cpus_allowed, u64 flags)
> @@ -1413,7 +1413,7 @@ BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu_node, KF_RCU)
> BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu, KF_RCU)
> BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu_node, KF_RCU)
> BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu, KF_RCU)
> -BTF_ID_FLAGS(func, __scx_bpf_select_cpu_and, KF_RCU)
> +BTF_ID_FLAGS(func, scx_bpf_select_cpu_and___v2, KF_RCU)
> BTF_ID_FLAGS(func, scx_bpf_select_cpu_and, KF_RCU)
> BTF_ID_FLAGS(func, scx_bpf_select_cpu_dfl, KF_RCU)
> BTF_KFUNCS_END(scx_kfunc_ids_idle)
> diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h
> index e65b1eb668ea5..64e5411d04c04 100644
> --- a/tools/sched_ext/include/scx/common.bpf.h
> +++ b/tools/sched_ext/include/scx/common.bpf.h
> @@ -60,9 +60,6 @@ static inline void ___vmlinux_h_sanity_check___(void)
>
> s32 scx_bpf_create_dsq(u64 dsq_id, s32 node) __ksym;
> s32 scx_bpf_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, bool *is_idle) __ksym;
> -s32 __scx_bpf_select_cpu_and(struct task_struct *p, const struct cpumask *cpus_allowed,
> - struct scx_bpf_select_cpu_and_args *args) __ksym __weak;
> -bool __scx_bpf_dsq_insert_vtime(struct task_struct *p, struct scx_bpf_dsq_insert_vtime_args *args) __ksym __weak;
> u32 scx_bpf_dispatch_nr_slots(void) __ksym;
> void scx_bpf_dispatch_cancel(void) __ksym;
> bool scx_bpf_dsq_move_to_local(u64 dsq_id) __ksym __weak;
> diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h
> index a023b71991a6a..963ff3263c20b 100644
> --- a/tools/sched_ext/include/scx/compat.bpf.h
> +++ b/tools/sched_ext/include/scx/compat.bpf.h
> @@ -161,6 +161,25 @@ static inline struct task_struct *__COMPAT_scx_bpf_cpu_curr(int cpu)
> return rq ? rq->curr : NULL;
> }
>
> +/*
> + * v6.19: Mirror the following _args structs, to prevent build errors in
> + * kernels that don't have these structs defined yet.
> + *
> + * The kernel will carry these mirrored structs until v6.23 (see below).
> + */
> +struct scx_bpf_select_cpu_and_args {
> + s32 prev_cpu;
> + u64 wake_flags;
> + u64 flags;
> +};
> +
> +struct scx_bpf_dsq_insert_vtime_args {
> + u64 dsq_id;
> + u64 slice;
> + u64 vtime;
> + u64 enq_flags;
> +};
> +
This redefinition seems to cause compilation problems when compiling
the selftests on 6.19 w/ the patch (errors below). Turning the definitions
into declarations gets the tests to compile.
Maybe we can gate the definitions behind some ifdef? This issue aside,
compiling the tests on a 6.17 system and running them on a 6.19 system
still works, so everything else is in order.
# cd /linux/tools/sched_ext
# make -j9
In file included from scx_simple.bpf.c:23:
In file included from /linux/tools/sched_ext/include/scx/common.bpf.h:765:
/linux/tools/sched_ext/include/scx/compat.bpf.h:170:8: error: redefinition of
'scx_bpf_select_cpu_and_args'
170 | struct scx_bpf_select_cpu_and_args {
| ^
/linux/tools/sched_ext/build/include/vmlinux.h:83614:8: note: previous
definition
is here
83614 | struct scx_bpf_select_cpu_and_args {
| ^
In file included from scx_simple.bpf.c:23:
In file included from /linux/tools/sched_ext/include/scx/common.bpf.h:765:
/linux/tools/sched_ext/include/scx/compat.bpf.h:176:8: error: redefinition of
'scx_bpf_dsq_insert_vtime_args'
176 | struct scx_bpf_dsq_insert_vtime_args {
| ^
/linux/tools/sched_ext/build/include/vmlinux.h:83607:8: note: previous
definition
is here
83607 | struct scx_bpf_dsq_insert_vtime_args {
| ^
2 errors generated.
make: *** [Makefile:176:
/linux/tools/sched_ext/build/obj/sched_ext/scx_simple.bpf.o] Error 1
make: *** Waiting for unfinished jobs....
In file included from scx_qmap.bpf.c:25:
In file included from /linux/tools/sched_ext/include/scx/common.bpf.h:765:
/linux/tools/sched_ext/include/scx/compat.bpf.h:170:8: error: redefinition of
'scx_bpf_select_cpu_and_args'
170 | struct scx_bpf_select_cpu_and_args {
| ^
/linux/tools/sched_ext/build/include/vmlinux.h:83614:8: note: previous
definition
is here
83614 | struct scx_bpf_select_cpu_and_args {
| ^
In file included from scx_qmap.bpf.c:25:
In file included from /linux/tools/sched_ext/include/scx/common.bpf.h:765:
/linux/tools/sched_ext/include/scx/compat.bpf.h:176:8: error: redefinition of
'scx_bpf_dsq_insert_vtime_args'
176 | struct scx_bpf_dsq_insert_vtime_args {
| ^
/linux/tools/sched_ext/build/include/vmlinux.h:83607:8: note: previous
definition
is here
83607 | struct scx_bpf_dsq_insert_vtime_args {
| ^
2 errors generated.
make: *** [Makefile:176:
/linux/tools/sched_ext/build/obj/sched_ext/scx_qmap.bpf.o] Error 1
> /*
> * v6.19: To work around BPF maximum parameter limit, the following kfuncs are
> * replaced with variants that pack scalar arguments in a struct. Wrappers are
> @@ -170,12 +189,20 @@ static inline struct task_struct *__COMPAT_scx_bpf_cpu_curr(int cpu)
> * compatibility. After v6.23 release, remove the compat handling and move the
> * wrappers to common.bpf.h.
> */
> -s32 scx_bpf_select_cpu_and___compat(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
> - const struct cpumask *cpus_allowed, u64 flags) __ksym __weak;
> -void scx_bpf_dsq_insert_vtime___compat(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) __ksym __weak;
> +s32 scx_bpf_select_cpu_and___v2(struct task_struct *p, const struct cpumask *cpus_allowed,
> + struct scx_bpf_select_cpu_and_args *args) __ksym __weak;
> +
> +s32 scx_bpf_select_cpu_and(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
> + const struct cpumask *cpus_allowed, u64 flags) __ksym __weak;
> +
> +bool scx_bpf_dsq_insert_vtime___v2(struct task_struct *p,
> + struct scx_bpf_dsq_insert_vtime_args *args) __ksym __weak;
> +
> +void scx_bpf_dsq_insert_vtime(struct task_struct *p,
> + u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) __ksym __weak;
>
> /**
> - * scx_bpf_select_cpu_and - Pick an idle CPU usable by task @p
> + * __COMPAT_scx_bpf_select_cpu_and - Pick an idle CPU usable by task @p
> * @p: task_struct to select a CPU for
> * @prev_cpu: CPU @p was on previously
> * @wake_flags: %SCX_WAKE_* flags
> @@ -183,11 +210,12 @@ void scx_bpf_dsq_insert_vtime___compat(struct task_struct *p, u64 dsq_id, u64 sl
> * @flags: %SCX_PICK_IDLE* flags
> *
> * Inline wrapper that packs scalar arguments into a struct and calls
> - * __scx_bpf_select_cpu_and(). See __scx_bpf_select_cpu_and() for details.
> + * scx_bpf_select_cpu_and___v2(). See scx_bpf_select_cpu_and___v2() for
> + * details.
> */
> static inline s32
> -scx_bpf_select_cpu_and(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
> - const struct cpumask *cpus_allowed, u64 flags)
> +__COMPAT_scx_bpf_select_cpu_and(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
> + const struct cpumask *cpus_allowed, u64 flags)
> {
> if (bpf_core_type_exists(struct scx_bpf_select_cpu_and_args)) {
> struct scx_bpf_select_cpu_and_args args = {
> @@ -196,15 +224,16 @@ scx_bpf_select_cpu_and(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
> .flags = flags,
> };
>
> - return __scx_bpf_select_cpu_and(p, cpus_allowed, &args);
> + return scx_bpf_select_cpu_and___v2(p, cpus_allowed, &args);
> } else {
> - return scx_bpf_select_cpu_and___compat(p, prev_cpu, wake_flags,
> - cpus_allowed, flags);
> + return scx_bpf_select_cpu_and(p, prev_cpu, wake_flags,
> + cpus_allowed, flags);
> }
> }
>
> /**
> - * scx_bpf_dsq_insert_vtime - Insert a task into the vtime priority queue of a DSQ
> + * __COMPAT_scx_bpf_dsq_insert_vtime - Insert a task into the vtime
> + * priority queue of a DSQ
> * @p: task_struct to insert
> * @dsq_id: DSQ to insert into
> * @slice: duration @p can run for in nsecs, 0 to keep the current value
> @@ -212,11 +241,12 @@ scx_bpf_select_cpu_and(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
> * @enq_flags: SCX_ENQ_*
> *
> * Inline wrapper that packs scalar arguments into a struct and calls
> - * __scx_bpf_dsq_insert_vtime(). See __scx_bpf_dsq_insert_vtime() for details.
> + * scx_bpf_dsq_insert_vtime___v2(). See scx_bpf_dsq_insert_vtime___v2() for
> + * details.
> */
> static inline bool
> -scx_bpf_dsq_insert_vtime(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime,
> - u64 enq_flags)
> +__COMPAT_scx_bpf_dsq_insert_vtime(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime,
> + u64 enq_flags)
> {
> if (bpf_core_type_exists(struct scx_bpf_dsq_insert_vtime_args)) {
> struct scx_bpf_dsq_insert_vtime_args args = {
> @@ -226,10 +256,9 @@ scx_bpf_dsq_insert_vtime(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime
> .enq_flags = enq_flags,
> };
>
> - return __scx_bpf_dsq_insert_vtime(p, &args);
> + return scx_bpf_dsq_insert_vtime___v2(p, &args);
> } else {
> - scx_bpf_dsq_insert_vtime___compat(p, dsq_id, slice, vtime,
> - enq_flags);
> + scx_bpf_dsq_insert_vtime(p, dsq_id, slice, vtime, enq_flags);
> return true;
> }
> }
> --
> 2.51.1
>
Thanks,
Emil
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