[PATCH mmotm] mm: vmscan: fix shrinker_rwsem in free_shrinker_info()
From: Hugh Dickins <hughd@google.com>
Date: 2021-03-30 23:45:28
Also in:
lkml, oe-lkp
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 <redacted> Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Yang Shi <redacted> --- 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)