Re: [PATCH sched_ext/for-7.2] sched_ext: Add __printf format attributes to scx_vexit() and bstr formatters

[Andrea Righi]

Hi Tejun,

On Mon, May 04, 2026 at 11:20:52AM -1000, Tejun Heo wrote:
> scx_vexit() forwards (fmt, args) to vscnprintf(); bstr_format() and
> __bstr_format() forward fmt to bstr_printf(); the BPF kfunc wrappers
> scx_bpf_exit_bstr(), scx_bpf_error_bstr() and scx_bpf_dump_bstr() in
> turn forward fmt to those formatters. None of them have __printf(),
> so clang -Wmissing-format-attribute fires on the forwarded calls and
> C-side callers don't get format-string checking.
> 
> Annotate the six functions with __printf(N, 0) matching the fmt
> parameter position in each.
> 
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Closes: https://lore.kernel.org/all/202605041112.Y6OG7v9r-lkp@xxxxxxxxx/
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>

Ah, thanks for fixing this, looks good!

Reviewed-by: Andrea Righi <arighi@xxxxxxxxxx>

-Andrea

> ---
>  kernel/sched/ext.c          | 5 +++++
>  kernel/sched/ext_internal.h | 5 +++--
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 966a846c213c..7ac7d10a41be 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -9338,6 +9338,7 @@ __bpf_kfunc void scx_bpf_reenqueue_local___v2(const struct bpf_prog_aux *aux)
> 
>  __bpf_kfunc_end_defs();
> 
> +__printf(5, 0)
>  static s32 __bstr_format(struct scx_sched *sch, u64 *data_buf, char *line_buf,
>  			 size_t line_size, char *fmt, unsigned long long *data,
>  			 u32 data__sz)
> @@ -9375,6 +9376,7 @@ static s32 __bstr_format(struct scx_sched *sch, u64 *data_buf, char *line_buf,
>  	return ret;
>  }
> 
> +__printf(3, 0)
>  static s32 bstr_format(struct scx_sched *sch, struct scx_bstr_buf *buf,
>  		       char *fmt, unsigned long long *data, u32 data__sz)
>  {
> @@ -9395,6 +9397,7 @@ __bpf_kfunc_start_defs();
>   * Indicate that the BPF scheduler wants to exit gracefully, and initiate ops
>   * disabling.
>   */
> +__printf(2, 0)
>  __bpf_kfunc void scx_bpf_exit_bstr(s64 exit_code, char *fmt,
>  				   unsigned long long *data, u32 data__sz,
>  				   const struct bpf_prog_aux *aux)
> @@ -9420,6 +9423,7 @@ __bpf_kfunc void scx_bpf_exit_bstr(s64 exit_code, char *fmt,
>   * Indicate that the BPF scheduler encountered a fatal error and initiate ops
>   * disabling.
>   */
> +__printf(1, 0)
>  __bpf_kfunc void scx_bpf_error_bstr(char *fmt, unsigned long long *data,
>  				    u32 data__sz, const struct bpf_prog_aux *aux)
>  {
> @@ -9447,6 +9451,7 @@ __bpf_kfunc void scx_bpf_error_bstr(char *fmt, unsigned long long *data,
>   * The extra dump may be multiple lines. A single line may be split over
>   * multiple calls. The last line is automatically terminated.
>   */
> +__printf(1, 0)
>  __bpf_kfunc void scx_bpf_dump_bstr(char *fmt, unsigned long long *data,
>  				   u32 data__sz, const struct bpf_prog_aux *aux)
>  {
> diff --git a/kernel/sched/ext_internal.h b/kernel/sched/ext_internal.h
> index b4f5dd28855e..0ed79bd891c7 100644
> --- a/kernel/sched/ext_internal.h
> +++ b/kernel/sched/ext_internal.h
> @@ -1477,8 +1477,9 @@ int scx_kfunc_context_filter(const struct bpf_prog *prog, u32 kfunc_id);
> 
>  bool scx_cpu_valid(struct scx_sched *sch, s32 cpu, const char *where);
> 
> -bool scx_vexit(struct scx_sched *sch, enum scx_exit_kind kind, s64 exit_code,
> -	       s32 exit_cpu, const char *fmt, va_list args);
> +__printf(5, 0) bool scx_vexit(struct scx_sched *sch, enum scx_exit_kind kind,
> +			      s64 exit_code, s32 exit_cpu, const char *fmt,
> +			      va_list args);
>  __printf(5, 6) bool __scx_exit(struct scx_sched *sch, enum scx_exit_kind kind,
>  			       s64 exit_code, s32 exit_cpu, const char *fmt, ...);
> 
> --
> 2.47.0