Re: [PATCH bpf-next v3 2/6] bpf: Allow per unit prefill for non-fix-size percpu memory allocator

Re: [PATCH bpf-next v3 2/6] bpf: Allow per unit prefill for non-fix-size percpu memory allocator

[kernel test robot]

Hi Yonghong,

kernel test robot noticed the following build warnings:

[auto build test WARNING on bpf-next/master]

url:    https://github.com/intel-lab-lkp/linux/commits/Yonghong-Song/bpf-Avoid-unnecessary-extra-percpu-memory-allocation/20231216-103310
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
patch link:    https://lore.kernel.org/r/20231216023015.3741144-1-yonghong.song%40linux.dev
patch subject: [PATCH bpf-next v3 2/6] bpf: Allow per unit prefill for non-fix-size percpu memory allocator
config: x86_64-randconfig-003-20231216 (https://download.01.org/0day-ci/archive/20231216/202312162351.UuoFmjJk-lkp@intel.com/config)
compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231216/202312162351.UuoFmjJk-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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202312162351.UuoFmjJk-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/bpf/memalloc.c:665:14: warning: variable 'objcg' is uninitialized when used here [-Wuninitialized]
                   c->objcg = objcg;
                              ^~~~~
   kernel/bpf/memalloc.c:642:26: note: initialize the variable 'objcg' to silence this warning
           struct obj_cgroup *objcg;
                                   ^
                                    = NULL
   1 warning generated.


vim +/objcg +665 kernel/bpf/memalloc.c

   637	
   638	int bpf_mem_alloc_percpu_unit_init(struct bpf_mem_alloc *ma, int size)
   639	{
   640		int cpu, i, err = 0, unit_size, percpu_size;
   641		struct bpf_mem_caches *cc, __percpu *pcc;
   642		struct obj_cgroup *objcg;
   643		struct bpf_mem_cache *c;
   644	
   645		i = bpf_mem_cache_idx(size);
   646		if (i < 0)
   647			return -EINVAL;
   648	
   649		/* room for llist_node and per-cpu pointer */
   650		percpu_size = LLIST_NODE_SZ + sizeof(void *);
   651	
   652		pcc = ma->caches;
   653		unit_size = sizes[i];
   654	
   655	#ifdef CONFIG_MEMCG_KMEM
   656		objcg = get_obj_cgroup_from_current();
   657	#endif
   658		for_each_possible_cpu(cpu) {
   659			cc = per_cpu_ptr(pcc, cpu);
   660			c = &cc->cache[i];
   661			if (cpu == 0 && c->unit_size)
   662				goto out;
   663	
   664			c->unit_size = unit_size;
 > 665			c->objcg = objcg;
   666			c->percpu_size = percpu_size;
   667			c->tgt = c;
   668	
   669			init_refill_work(c);
   670			prefill_mem_cache(c, cpu);
   671	
   672			if (cpu == 0) {
   673				err = check_obj_size(c, i);
   674				if (err) {
   675					drain_mem_cache(c);
   676					memset(c, 0, sizeof(*c));
   677					goto out;
   678				}
   679			}
   680		}
   681	
   682	out:
   683		return err;
   684	}
   685	

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https://github.com/intel/lkp-tests/wiki