kernel/sched/ext/arena.c uses the gen_pool allocator, which is built only
when GENERIC_ALLOCATOR is set. SCHED_CLASS_EXT doesn't select it, so on
configs where nothing else does, the build fails to link:

  build_policy.o: undefined reference to `gen_pool_create'
  build_policy.o: undefined reference to `gen_pool_for_each_chunk'
  build_policy.o: undefined reference to `gen_pool_destroy'

Fixes: 9eca087deb0b ("sched_ext: Sub-allocator over kernel-claimed BPF arena pages")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202608151315.tvN3X0Oq-lkp@intel.com/
Closes: https://lore.kernel.org/oe-kbuild-all/202608151632.3p91bTQj-lkp@intel.com/
Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/Kconfig.preempt |    1 +
 1 file changed, 1 insertion(+)

--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -169,6 +169,7 @@ config SCHED_CORE
 config SCHED_CLASS_EXT
 	bool "Extensible Scheduling Class"
 	depends on BPF_SYSCALL && BPF_JIT && DEBUG_INFO_BTF
+	select GENERIC_ALLOCATOR
 	select STACKTRACE if STACKTRACE_SUPPORT
 	help
 	  This option enables a new scheduler class sched_ext (SCX), which

Don't kick yourself in the face too hard because you applied it, but since
this is in base kernel/, and I understand it, I'll review it! :)


>build_policy.o: undefined 
>reference to `gen_pool_create'
>build_policy.o: undefined >reference to >`gen_pool_for_each_chunk'
>build_policy.o: undefined >reference to `gen_pool_destroy'

gnarly! But, why adapt to "hppa"? Its literally been "fully" retired since
2021!


Someone in the kernel, no idea who, said "Why need to adapt to these old
architectures? Why can't they just fork it and fix it OOT?"


But that's more an opinion thing, in my opinion it should just be OOT, but
the people who work on hppa will be pissed.


Heh. Just know that was a small rant, anyway, good patch 

Reviewed-by: Bradley Morgan <include@grrlz.net>

Thanks!

Applied to sched_ext/for-7.3.

Thanks.

-- 
tejun