linux-kernel - mm/list_lru.c:514:3-8: WARNING: NULL check before some freeing functions is not needed.

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Message-ID: <202412290924.UTP7GH2Z-lkp@intel.com>
Date: Sun, 29 Dec 2024 09:59:48 +0800
From: kernel test robot <lkp@...el.com>
To: Kairui Song <kasong@...cent.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>
Subject: mm/list_lru.c:514:3-8: WARNING: NULL check before some freeing
 functions is not needed.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   059dd502b263d8a4e2a84809cf1068d6a3905e6f
commit: 28e98022b31efdb8f1ba310d938cd9b97ededfe4 mm/list_lru: simplify reparenting and initial allocation
date:   7 weeks ago
config: i386-randconfig-054-20241229 (https://download.01.org/0day-ci/archive/20241229/202412290924.UTP7GH2Z-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0

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/202412290924.UTP7GH2Z-lkp@intel.com/

cocci warnings: (new ones prefixed by >>)
>> mm/list_lru.c:514:3-8: WARNING: NULL check before some freeing functions is not needed.

vim +514 mm/list_lru.c

   470	
   471	int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
   472				 gfp_t gfp)
   473	{
   474		unsigned long flags;
   475		struct list_lru_memcg *mlru;
   476		struct mem_cgroup *pos, *parent;
   477		XA_STATE(xas, &lru->xa, 0);
   478	
   479		if (!list_lru_memcg_aware(lru) || memcg_list_lru_allocated(memcg, lru))
   480			return 0;
   481	
   482		gfp &= GFP_RECLAIM_MASK;
   483		/*
   484		 * Because the list_lru can be reparented to the parent cgroup's
   485		 * list_lru, we should make sure that this cgroup and all its
   486		 * ancestors have allocated list_lru_memcg.
   487		 */
   488		do {
   489			/*
   490			 * Keep finding the farest parent that wasn't populated
   491			 * until found memcg itself.
   492			 */
   493			pos = memcg;
   494			parent = parent_mem_cgroup(pos);
   495			while (!memcg_list_lru_allocated(parent, lru)) {
   496				pos = parent;
   497				parent = parent_mem_cgroup(pos);
   498			}
   499	
   500			mlru = memcg_init_list_lru_one(gfp);
   501			if (!mlru)
   502				return -ENOMEM;
   503			xas_set(&xas, pos->kmemcg_id);
   504			do {
   505				xas_lock_irqsave(&xas, flags);
   506				if (!xas_load(&xas) && !css_is_dying(&pos->css)) {
   507					xas_store(&xas, mlru);
   508					if (!xas_error(&xas))
   509						mlru = NULL;
   510				}
   511				xas_unlock_irqrestore(&xas, flags);
   512			} while (xas_nomem(&xas, gfp));
   513			if (mlru)
 > 514				kfree(mlru);
   515		} while (pos != memcg && !css_is_dying(&pos->css));
   516	
   517		return xas_error(&xas);
   518	}
   519	#else
   520	static inline void memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
   521	{
   522	}
   523	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki