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Date: Fri, 14 Jun 2024 16:05:41 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: kernel test robot <lkp@...el.com>
Cc: oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Linux Memory Management List <linux-mm@...ck.org>, Kent Overstreet <kent.overstreet@...ux.dev>,
Kees Cook <keescook@...omium.org>, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: mm/slub.c:3905:29: error: variable 'obj_exts' set but not used
On Fri, Jun 14, 2024 at 2:09 PM kernel test robot <lkp@...el.com> wrote:
>
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head: c286c21ff94252f778515b21b6bebe749454a852
> commit: 4b8736964640fe160724e7135dc62883bddcdace mm/slab: add allocation accounting into slab allocation and free paths
> date: 7 weeks ago
> config: x86_64-sof-customedconfig-atom-defconfig (https://download.01.org/0day-ci/archive/20240615/202406150444.F6neSaiy-lkp@intel.com/config)
> compiler: gcc-11 (Ubuntu 11.4.0-4ubuntu1) 11.4.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240615/202406150444.F6neSaiy-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202406150444.F6neSaiy-lkp@intel.com/
>
> All errors (new ones prefixed by >>):
>
> mm/slub.c: In function 'slab_post_alloc_hook':
> >> mm/slub.c:3905:29: error: variable 'obj_exts' set but not used [-Werror=unused-but-set-variable]
> 3905 | struct slabobj_ext *obj_exts;
> | ^~~~~~~~
> cc1: all warnings being treated as errors
Fix is posted at
https://lore.kernel.org/all/20240614225951.3845577-1-surenb@google.com/
>
>
> vim +/obj_exts +3905 mm/slub.c
>
> 3898
> 3899 static __fastpath_inline
> 3900 void slab_post_alloc_hook(struct kmem_cache *s, struct obj_cgroup *objcg,
> 3901 gfp_t flags, size_t size, void **p, bool init,
> 3902 unsigned int orig_size)
> 3903 {
> 3904 unsigned int zero_size = s->object_size;
> > 3905 struct slabobj_ext *obj_exts;
> 3906 bool kasan_init = init;
> 3907 size_t i;
> 3908 gfp_t init_flags = flags & gfp_allowed_mask;
> 3909
> 3910 /*
> 3911 * For kmalloc object, the allocated memory size(object_size) is likely
> 3912 * larger than the requested size(orig_size). If redzone check is
> 3913 * enabled for the extra space, don't zero it, as it will be redzoned
> 3914 * soon. The redzone operation for this extra space could be seen as a
> 3915 * replacement of current poisoning under certain debug option, and
> 3916 * won't break other sanity checks.
> 3917 */
> 3918 if (kmem_cache_debug_flags(s, SLAB_STORE_USER | SLAB_RED_ZONE) &&
> 3919 (s->flags & SLAB_KMALLOC))
> 3920 zero_size = orig_size;
> 3921
> 3922 /*
> 3923 * When slab_debug is enabled, avoid memory initialization integrated
> 3924 * into KASAN and instead zero out the memory via the memset below with
> 3925 * the proper size. Otherwise, KASAN might overwrite SLUB redzones and
> 3926 * cause false-positive reports. This does not lead to a performance
> 3927 * penalty on production builds, as slab_debug is not intended to be
> 3928 * enabled there.
> 3929 */
> 3930 if (__slub_debug_enabled())
> 3931 kasan_init = false;
> 3932
> 3933 /*
> 3934 * As memory initialization might be integrated into KASAN,
> 3935 * kasan_slab_alloc and initialization memset must be
> 3936 * kept together to avoid discrepancies in behavior.
> 3937 *
> 3938 * As p[i] might get tagged, memset and kmemleak hook come after KASAN.
> 3939 */
> 3940 for (i = 0; i < size; i++) {
> 3941 p[i] = kasan_slab_alloc(s, p[i], init_flags, kasan_init);
> 3942 if (p[i] && init && (!kasan_init ||
> 3943 !kasan_has_integrated_init()))
> 3944 memset(p[i], 0, zero_size);
> 3945 kmemleak_alloc_recursive(p[i], s->object_size, 1,
> 3946 s->flags, init_flags);
> 3947 kmsan_slab_alloc(s, p[i], init_flags);
> 3948 if (need_slab_obj_ext()) {
> 3949 obj_exts = prepare_slab_obj_exts_hook(s, flags, p[i]);
> 3950 #ifdef CONFIG_MEM_ALLOC_PROFILING
> 3951 /*
> 3952 * Currently obj_exts is used only for allocation profiling.
> 3953 * If other users appear then mem_alloc_profiling_enabled()
> 3954 * check should be added before alloc_tag_add().
> 3955 */
> 3956 if (likely(obj_exts))
> 3957 alloc_tag_add(&obj_exts->ref, current->alloc_tag, s->size);
> 3958 #endif
> 3959 }
> 3960 }
> 3961
> 3962 memcg_slab_post_alloc_hook(s, objcg, flags, size, p);
> 3963 }
> 3964
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
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