Re: [PATCH bpf] bpf: Make migrate_{disable,enable} always inline if in header file

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Oct 29, 2025 at 06:13:21PM -0700, Alexei Starovoitov wrote:
> On Wed, Oct 29, 2025 at 11:37 AM Yonghong Song <yonghong.song@linux.dev> wrote:
> >
> > With latest bpf/bpf-next tree and latest pahole master, I got the following
> > build failure:
> >
> >   $ make LLVM=1 -j
> >     ...
> >     LD      vmlinux.o
> >     GEN     .vmlinux.objs
> >     ...
> >     BTF     .tmp_vmlinux1.btf.o
> >     ...
> >     AS      .tmp_vmlinux2.kallsyms.o
> >     LD      vmlinux.unstripped
> >     BTFIDS  vmlinux.unstripped
> >   WARN: resolve_btfids: unresolved symbol migrate_enable
> >   WARN: resolve_btfids: unresolved symbol migrate_disable
> >   make[2]: *** [/home/yhs/work/bpf-next/scripts/Makefile.vmlinux:72: vmlinux.unstripped] Error 255
> >   make[2]: *** Deleting file 'vmlinux.unstripped'
> >   make[1]: *** [/home/yhs/work/bpf-next/Makefile:1242: vmlinux] Error 2
> >   make: *** [/home/yhs/work/bpf-next/Makefile:248: __sub-make] Error 2
> >
> > In pahole patch [1], if two functions having identical names but different
> > addresses, then this function name is considered ambiguous and later on
> > this function will not be added to vmlinux/module BTF.
> >
> > Commit 378b7708194f ("sched: Make migrate_{en,dis}able() inline") changed
> > original global funcitons migrate_{enable,disable} to
> >   - in kernel/sched/core.c, migrate_{enable,disable} are global funcitons.
> >   - in other places, migrate_{enable,disable} may survive as static functions
> >     since they are marked as 'inline' in include/linux/sched.h and the
> >     'inline' attribute does not garantee inlining.
> >
> > If I build with clang compiler (make LLVM=1 -j) (llvm21 and llvm22), I found
> > there are four symbols for migrate_{enable,disable} respectively, three
> > static functions and one global function. With the above pahole patch [1],
> > migrate_{enable,disable} are not in vmlinux BTF and this will cause
> > later resolve_btfids failure.
> >
> > Making migrate_{enable,disable} always inline in include/linux/sched.h
> > can fix the problem.
> >
> >   [1] https://lore.kernel.org/dwarves/79a329ef-9bb3-454e-9135-731f2fd51951@oracle.com/
> >
> > Fixes: 378b7708194f ("sched: Make migrate_{en,dis}able() inline")
> > Cc: Menglong Dong <menglong8.dong@gmail.com>
> > Cc: Ihor Solodrai <ihor.solodrai@linux.dev>
> > Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
> > ---
> >  include/linux/sched.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index cbb7340c5866..b469878de25c 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -2407,12 +2407,12 @@ static inline void __migrate_enable(void) { }
> >   * be defined in kernel/sched/core.c.
> >   */
> >  #ifndef INSTANTIATE_EXPORTED_MIGRATE_DISABLE
> > -static inline void migrate_disable(void)
> > +static __always_inline void migrate_disable(void)
> >  {
> >         __migrate_disable();
> >  }
> >
> > -static inline void migrate_enable(void)
> > +static __always_inline void migrate_enable(void)
> >  {
> >         __migrate_enable();
> >  }
> 
> Peter,
> 
> Are you ok if we take this?

Yes, but WTH would clang not inline this trivial function to begin with?