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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id j129sm228556qkf.110.2021.03.30.16.44.17 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Tue, 30 Mar 2021 16:44:18 -0700 (PDT) Date: Tue, 30 Mar 2021 16:44:05 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Andrew Morton cc: kernel test robot , Yang Shi , Stephen Rothwell , Roman Gushchin , Kirill Tkhai , Vlastimil Babka , Shakeel Butt , Dave Chinner , Johannes Weiner , Michal Hocko , LKML , Linux Memory Management List , lkp@lists.01.org, lkp@intel.com Subject: [PATCH mmotm] mm: vmscan: fix shrinker_rwsem in free_shrinker_info() Message-ID: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Lockdep warns mm/vmscan.c: suspicious rcu_dereference_protected() usage! when free_shrinker_info() is called from mem_cgroup_css_free(): there it is called with no locking, whereas alloc_shrinker_info() calls it with down_write of shrinker_rwsem - which seems appropriate. Rearrange that so free_shrinker_info() can manage the shrinker_rwsem for itself. Link: https://lkml.kernel.org/r/20210317140615.GB28839@xsang-OptiPlex-9020 Reported-by: kernel test robot Signed-off-by: Hugh Dickins Cc: Yang Shi --- Sorry, I've made no attempt to work out precisely where in the series the locking went missing, nor tried to fit this in as a fix on top of mm-vmscan-add-shrinker_info_protected-helper.patch which Oliver reported (and which you notated in mmotm's "series" file). This patch just adds the fix to the end of the series, after mm-vmscan-shrink-deferred-objects-proportional-to-priority.patch mm/vmscan.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) --- mmotm/mm/vmscan.c 2021-03-28 17:26:54.935553064 -0700 +++ linux/mm/vmscan.c 2021-03-30 15:55:13.374459559 -0700 @@ -249,18 +249,20 @@ void free_shrinker_info(struct mem_cgrou struct shrinker_info *info; int nid; + down_write(&shrinker_rwsem); for_each_node(nid) { pn = memcg->nodeinfo[nid]; info = shrinker_info_protected(memcg, nid); kvfree(info); rcu_assign_pointer(pn->shrinker_info, NULL); } + up_write(&shrinker_rwsem); } int alloc_shrinker_info(struct mem_cgroup *memcg) { struct shrinker_info *info; - int nid, size, ret = 0; + int nid, size; int map_size, defer_size = 0; down_write(&shrinker_rwsem); @@ -270,9 +272,9 @@ int alloc_shrinker_info(struct mem_cgrou for_each_node(nid) { info = kvzalloc_node(sizeof(*info) + size, GFP_KERNEL, nid); if (!info) { + up_write(&shrinker_rwsem); free_shrinker_info(memcg); - ret = -ENOMEM; - break; + return -ENOMEM; } info->nr_deferred = (atomic_long_t *)(info + 1); info->map = (void *)info->nr_deferred + defer_size; @@ -280,7 +282,7 @@ int alloc_shrinker_info(struct mem_cgrou } up_write(&shrinker_rwsem); - return ret; + return 0; } static inline bool need_expand(int nr_max)