[akpm-mm:mm-new 331/335] mm/memcontrol-v1.c:685 memcg1_swapout() warn: inconsistent returns 'rcu_read'.

[akpm-mm:mm-new 331/335] mm/memcontrol-v1.c:685 memcg1_swapout() warn: inconsistent returns 'rcu_read'.

[Dan Carpenter]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-new
head:   78d5565acc4516dfe1fe5a3779a53bc7aaedc2e1
commit: 8e5f42f2bf326f0efb1e565fa57b5ef99b40e646 [331/335] mm: memcontrol: eliminate the problem of dying memory cgroup for LRU folios
config: parisc-randconfig-r072-20260115 (https://download.01.org/0day-ci/archive/20260115/202601151810.ie4EgP4S-lkp@intel.com/config)
compiler: hppa-linux-gcc (GCC) 13.4.0
smatch version: v0.5.0-8985-g2614ff1a

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>
| Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
| Closes: https://lore.kernel.org/r/202601151810.ie4EgP4S-lkp@intel.com/

smatch warnings:
mm/memcontrol-v1.c:685 memcg1_swapout() warn: inconsistent returns 'rcu_read'.

vim +/rcu_read +685 mm/memcontrol-v1.c

89ce924f0bd447 Johannes Weiner    2025-01-24  613  void memcg1_swapout(struct folio *folio, swp_entry_t entry)
f7d49ba03ae755 Shakeel Butt       2024-08-14  614  {
89ce924f0bd447 Johannes Weiner    2025-01-24  615  	struct mem_cgroup *memcg, *swap_memcg;
8e5f42f2bf326f Muchun Song        2026-01-14  616  	struct obj_cgroup *objcg;
89ce924f0bd447 Johannes Weiner    2025-01-24  617  	unsigned int nr_entries;
8cb494d6e92a26 Deepanshu Kartikey 2026-01-10  618  	unsigned short oldid;
89ce924f0bd447 Johannes Weiner    2025-01-24  619  
89ce924f0bd447 Johannes Weiner    2025-01-24  620  	VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
89ce924f0bd447 Johannes Weiner    2025-01-24  621  	VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);
89ce924f0bd447 Johannes Weiner    2025-01-24  622  
89ce924f0bd447 Johannes Weiner    2025-01-24  623  	if (mem_cgroup_disabled())
89ce924f0bd447 Johannes Weiner    2025-01-24  624  		return;
89ce924f0bd447 Johannes Weiner    2025-01-24  625  
89ce924f0bd447 Johannes Weiner    2025-01-24  626  	if (!do_memsw_account())
89ce924f0bd447 Johannes Weiner    2025-01-24  627  		return;
89ce924f0bd447 Johannes Weiner    2025-01-24  628  
8e5f42f2bf326f Muchun Song        2026-01-14  629  	objcg = folio_objcg(folio);
8e5f42f2bf326f Muchun Song        2026-01-14  630  	VM_WARN_ON_ONCE_FOLIO(!objcg, folio);
8e5f42f2bf326f Muchun Song        2026-01-14  631  	if (!objcg)
89ce924f0bd447 Johannes Weiner    2025-01-24  632  		return;
89ce924f0bd447 Johannes Weiner    2025-01-24  633  
8e5f42f2bf326f Muchun Song        2026-01-14  634  	rcu_read_lock();
8e5f42f2bf326f Muchun Song        2026-01-14  635  	memcg = obj_cgroup_memcg(objcg);
8cb494d6e92a26 Deepanshu Kartikey 2026-01-10  636  	/*
8cb494d6e92a26 Deepanshu Kartikey 2026-01-10  637  	 * Check if this swap entry is already recorded. This can happen
8cb494d6e92a26 Deepanshu Kartikey 2026-01-10  638  	 * when MADV_PAGEOUT is called multiple times on pages that remain
8cb494d6e92a26 Deepanshu Kartikey 2026-01-10  639  	 * in swapcache, reusing the same swap entries.
8cb494d6e92a26 Deepanshu Kartikey 2026-01-10  640  	 */
8cb494d6e92a26 Deepanshu Kartikey 2026-01-10  641  	oldid = lookup_swap_cgroup_id(entry);
8cb494d6e92a26 Deepanshu Kartikey 2026-01-10  642  	if (oldid == mem_cgroup_id(memcg))
8cb494d6e92a26 Deepanshu Kartikey 2026-01-10  643  		return;


rcu_read_unlock() before returning

8cb494d6e92a26 Deepanshu Kartikey 2026-01-10  644  	VM_WARN_ON_ONCE(oldid != 0);
8cb494d6e92a26 Deepanshu Kartikey 2026-01-10  645  
89ce924f0bd447 Johannes Weiner    2025-01-24  646  	/*
89ce924f0bd447 Johannes Weiner    2025-01-24  647  	 * In case the memcg owning these pages has been offlined and doesn't
89ce924f0bd447 Johannes Weiner    2025-01-24  648  	 * have an ID allocated to it anymore, charge the closest online
89ce924f0bd447 Johannes Weiner    2025-01-24  649  	 * ancestor for the swap instead and transfer the memory+swap charge.
89ce924f0bd447 Johannes Weiner    2025-01-24  650  	 */
1d7634095c770c Shakeel Butt       2025-12-25  651  	swap_memcg = mem_cgroup_private_id_get_online(memcg);
89ce924f0bd447 Johannes Weiner    2025-01-24  652  	nr_entries = folio_nr_pages(folio);
89ce924f0bd447 Johannes Weiner    2025-01-24  653  	/* Get references for the tail pages, too */
89ce924f0bd447 Johannes Weiner    2025-01-24  654  	if (nr_entries > 1)
1d7634095c770c Shakeel Butt       2025-12-25  655  		mem_cgroup_private_id_get_many(swap_memcg, nr_entries - 1);
89ce924f0bd447 Johannes Weiner    2025-01-24  656  	mod_memcg_state(swap_memcg, MEMCG_SWAP, nr_entries);
89ce924f0bd447 Johannes Weiner    2025-01-24  657  
1d7634095c770c Shakeel Butt       2025-12-25  658  	swap_cgroup_record(folio, mem_cgroup_private_id(swap_memcg), entry);
89ce924f0bd447 Johannes Weiner    2025-01-24  659  
89ce924f0bd447 Johannes Weiner    2025-01-24  660  	folio_unqueue_deferred_split(folio);
89ce924f0bd447 Johannes Weiner    2025-01-24  661  	folio->memcg_data = 0;
89ce924f0bd447 Johannes Weiner    2025-01-24  662  
8e5f42f2bf326f Muchun Song        2026-01-14  663  	if (!obj_cgroup_is_root(objcg))
89ce924f0bd447 Johannes Weiner    2025-01-24  664  		page_counter_uncharge(&memcg->memory, nr_entries);
89ce924f0bd447 Johannes Weiner    2025-01-24  665  
89ce924f0bd447 Johannes Weiner    2025-01-24  666  	if (memcg != swap_memcg) {
89ce924f0bd447 Johannes Weiner    2025-01-24  667  		if (!mem_cgroup_is_root(swap_memcg))
89ce924f0bd447 Johannes Weiner    2025-01-24  668  			page_counter_charge(&swap_memcg->memsw, nr_entries);
89ce924f0bd447 Johannes Weiner    2025-01-24  669  		page_counter_uncharge(&memcg->memsw, nr_entries);
89ce924f0bd447 Johannes Weiner    2025-01-24  670  	}
89ce924f0bd447 Johannes Weiner    2025-01-24  671  
f7d49ba03ae755 Shakeel Butt       2024-08-14  672  	/*
f7d49ba03ae755 Shakeel Butt       2024-08-14  673  	 * Interrupts should be disabled here because the caller holds the
f7d49ba03ae755 Shakeel Butt       2024-08-14  674  	 * i_pages lock which is taken with interrupts-off. It is
f7d49ba03ae755 Shakeel Butt       2024-08-14  675  	 * important here to have the interrupts disabled because it is the
f7d49ba03ae755 Shakeel Butt       2024-08-14  676  	 * only synchronisation we have for updating the per-CPU variables.
f7d49ba03ae755 Shakeel Butt       2024-08-14  677  	 */
f7d49ba03ae755 Shakeel Butt       2024-08-14  678  	preempt_disable_nested();
f7d49ba03ae755 Shakeel Butt       2024-08-14  679  	VM_WARN_ON_IRQS_ENABLED();
f7d49ba03ae755 Shakeel Butt       2024-08-14  680  	memcg1_charge_statistics(memcg, -folio_nr_pages(folio));
f7d49ba03ae755 Shakeel Butt       2024-08-14  681  	preempt_enable_nested();
f7d49ba03ae755 Shakeel Butt       2024-08-14  682  	memcg1_check_events(memcg, folio_nid(folio));
89ce924f0bd447 Johannes Weiner    2025-01-24  683  
8e5f42f2bf326f Muchun Song        2026-01-14  684  	rcu_read_unlock();
8e5f42f2bf326f Muchun Song        2026-01-14 @685  	obj_cgroup_put(objcg);
89ce924f0bd447 Johannes Weiner    2025-01-24  686  }

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