mm/slab: fix 'variable obj_exts set but not used' warning

slab_post_alloc_hook() uses prepare_slab_obj_exts_hook() to obtain
slabobj_ext object.  Currently the only user of slabobj_ext object in this
path is memory allocation profiling, therefore when it's not enabled this
object is not needed.  This also generates a warning when compiling with
CONFIG_MEM_ALLOC_PROFILING=n.  Move the code under this configuration to
fix the warning.  If more slabobj_ext users appear in the future, the code
will have to be changed back to call prepare_slab_obj_exts_hook().

Link: https://lkml.kernel.org/r/20240614225951.3845577-1-surenb@google.com
Fixes: 4b8736964640 ("mm/slab: add allocation accounting into slab allocation and free paths")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202406150444.F6neSaiy-lkp@intel.com/
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Kees Cook <keescook@chromium.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/slub.c b/mm/slub.c
index 1373ac365a46f47c143c4c00998139f7d37457e7..4927edec6a8c938ba5902c45d6da4ef0eaf55d6c 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3902,7 +3902,6 @@ bool slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
                          unsigned int orig_size)
 {
        unsigned int zero_size = s->object_size;
-       struct slabobj_ext *obj_exts;
        bool kasan_init = init;
        size_t i;
        gfp_t init_flags = flags & gfp_allowed_mask;
@@ -3945,9 +3944,11 @@ bool slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
                kmemleak_alloc_recursive(p[i], s->object_size, 1,
                                         s->flags, init_flags);
                kmsan_slab_alloc(s, p[i], init_flags);
+#ifdef CONFIG_MEM_ALLOC_PROFILING
                if (need_slab_obj_ext()) {
+                       struct slabobj_ext *obj_exts;
+
                        obj_exts = prepare_slab_obj_exts_hook(s, flags, p[i]);
-#ifdef CONFIG_MEM_ALLOC_PROFILING
                        /*
                         * Currently obj_exts is used only for allocation profiling.
                         * If other users appear then mem_alloc_profiling_enabled()
@@ -3955,8 +3956,8 @@ bool slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
                         */
                        if (likely(obj_exts))
                                alloc_tag_add(&obj_exts->ref, current->alloc_tag, s->size);
-#endif
                }
+#endif
        }
 
        return memcg_slab_post_alloc_hook(s, lru, flags, size, p);