linux-kernel - [PATCH 1/1] mm/slab: fix 'variable obj

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Date: Fri, 14 Jun 2024 15:59:51 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: akpm@...ux-foundation.org
Cc: kent.overstreet@...ux.dev, vbabka@...e.cz, pasha.tatashin@...een.com, 
	souravpanda@...gle.com, keescook@...omium.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Suren Baghdasaryan <surenb@...gle.com>, 
	kernel test robot <lkp@...el.com>
Subject: [PATCH 1/1] 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().

Fixes: 4b8736964640 ("mm/slab: add allocation accounting into slab allocation and free paths")
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202406150444.F6neSaiy-lkp@intel.com/
Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
---
 mm/slub.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 1373ac365a46..4927edec6a8c 100644
--- 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);

base-commit: c286c21ff94252f778515b21b6bebe749454a852
-- 
2.45.2.627.g7a2c4fd464-goog