This is an unusual situation so I thought it best to explain it in a separate patch.
"percpu: reduce the number of cpu distance comparisons" introduces a dependency on cpumask helper functions in __init code. This code references a struct cpumask annotated __initdata. When the function is inlined (gcc), everything is fine, but clang decides not to inline these function calls. This causes modpost to warn about an __initdata access by a function not annotated with __init [1]. Ways I thought about fixing it: 1. figure out why clang thinks this inlining is too costly. 2. create a wrapper function annotated __init (this). 3. annotate cpumask with __refdata. Ultimately it comes down to if it's worth saving the cpumask memory and allowing it to be freed. IIUC, __refdata won't be freed, so option 3 is just a little wasteful. 1 is out of my depth, leaving 2. I don't feel great about this behavior being dependent on inlining semantics, but cpumask helpers are small and probably should be inlined. modpost complaint: WARNING: modpost: vmlinux.o(.text+0x735425): Section mismatch in reference from the function cpumask_clear_cpu() to the variable .init.data:pcpu_build_alloc_info.mask The function cpumask_clear_cpu() references the variable __initdata pcpu_build_alloc_info.mask. This is often because cpumask_clear_cpu lacks a __initdata annotation or the annotation of pcpu_build_alloc_info.mask is wrong. clang output: mm/percpu.c:2724:5: remark: cpumask_clear_cpu not inlined into pcpu_build_alloc_info because too costly to inline (cost=725, threshold=325) [-Rpass-missed=inline] [1] https://lore.kernel.org/linux-mm/202012220454.9f6bkz9q-...@intel.com/ Reported-by: kernel test robot <l...@intel.com> Signed-off-by: Dennis Zhou <den...@kernel.org> --- This is on top of percpu#for-5.12. mm/percpu.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/mm/percpu.c b/mm/percpu.c index 80f8f885a990..357977c4cb00 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -2642,6 +2642,18 @@ early_param("percpu_alloc", percpu_alloc_setup); /* pcpu_build_alloc_info() is used by both embed and page first chunk */ #if defined(BUILD_EMBED_FIRST_CHUNK) || defined(BUILD_PAGE_FIRST_CHUNK) + +/* + * This wrapper is to avoid a warning where cpumask_clear_cpu() is not inlined + * when compiling with clang causing modpost to warn about accessing __initdata + * from a non __init function. By doing this, we allow the struct cpumask to be + * freed instead of it taking space by annotating with __refdata. + */ +static void __init pcpu_cpumask_clear_cpu(int cpu, struct cpumask *mask) +{ + cpumask_clear_cpu(cpu, mask); +} + /** * pcpu_build_alloc_info - build alloc_info considering distances between CPUs * @reserved_size: the size of reserved percpu area in bytes @@ -2713,7 +2725,7 @@ static struct pcpu_alloc_info * __init pcpu_build_alloc_info( cpu = cpumask_first(&mask); group_map[cpu] = group; group_cnt[group]++; - cpumask_clear_cpu(cpu, &mask); + pcpu_cpumask_clear_cpu(cpu, &mask); for_each_cpu(tcpu, &mask) { if (!cpu_distance_fn || @@ -2721,7 +2733,7 @@ static struct pcpu_alloc_info * __init pcpu_build_alloc_info( cpu_distance_fn(tcpu, cpu) == LOCAL_DISTANCE)) { group_map[tcpu] = group; group_cnt[group]++; - cpumask_clear_cpu(tcpu, &mask); + pcpu_cpumask_clear_cpu(tcpu, &mask); } } } -- 2.29.2.729.g45daf8777d-goog
