diff options
| author | Yang Shi <shy828301@gmail.com> | 2021-05-04 18:36:14 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2021-05-05 11:27:23 -0700 |
| commit | d27cf2aa0d26a221982d04757cc32db97833ec29 (patch) | |
| tree | 78db67ebfe16c90a3133a427cca92d289f5b4555 /mm/vmscan.c | |
| parent | 2bfd36374edd9ed7f2ebf66cacebedf7273901cb (diff) | |
mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation
Since memcg_shrinker_map_size just can be changed under holding
shrinker_rwsem exclusively, the read side can be protected by holding read
lock, so it sounds superfluous to have a dedicated mutex.
Kirill Tkhai suggested use write lock since:
* We want the assignment to shrinker_maps is visible for shrink_slab_memcg().
* The rcu_dereference_protected() dereferrencing in shrink_slab_memcg(), but
in case of we use READ lock in alloc_shrinker_maps(), the dereferrencing
is not actually protected.
* READ lock makes alloc_shrinker_info() racy against memory allocation fail.
alloc_shrinker_info()->free_shrinker_info() may free memory right after
shrink_slab_memcg() dereferenced it. You may say
shrink_slab_memcg()->mem_cgroup_online() protects us from it? Yes, sure,
but this is not the thing we want to remember in the future, since this
spreads modularity.
And a test with heavy paging workload didn't show write lock makes things worse.
Link: https://lkml.kernel.org/r/20210311190845.9708-4-shy828301@gmail.com
Signed-off-by: Yang Shi <shy828301@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Acked-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/vmscan.c')
| -rw-r--r-- | mm/vmscan.c | 18 |
1 files changed, 8 insertions, 10 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c index bead5ae1e7e2..d3fba55a0028 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -187,7 +187,6 @@ static DECLARE_RWSEM(shrinker_rwsem); #ifdef CONFIG_MEMCG static int memcg_shrinker_map_size; -static DEFINE_MUTEX(memcg_shrinker_map_mutex); static void free_shrinker_map_rcu(struct rcu_head *head) { @@ -201,8 +200,6 @@ static int expand_one_shrinker_map(struct mem_cgroup *memcg, struct mem_cgroup_per_node *pn; int nid; - lockdep_assert_held(&memcg_shrinker_map_mutex); - for_each_node(nid) { pn = memcg->nodeinfo[nid]; old = rcu_dereference_protected(pn->shrinker_map, true); @@ -250,7 +247,7 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg) if (mem_cgroup_is_root(memcg)) return 0; - mutex_lock(&memcg_shrinker_map_mutex); + down_write(&shrinker_rwsem); size = memcg_shrinker_map_size; for_each_node(nid) { map = kvzalloc_node(sizeof(*map) + size, GFP_KERNEL, nid); @@ -261,7 +258,7 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg) } rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_map, map); } - mutex_unlock(&memcg_shrinker_map_mutex); + up_write(&shrinker_rwsem); return ret; } @@ -276,9 +273,10 @@ static int expand_shrinker_maps(int new_id) if (size <= old_size) return 0; - mutex_lock(&memcg_shrinker_map_mutex); if (!root_mem_cgroup) - goto unlock; + goto out; + + lockdep_assert_held(&shrinker_rwsem); memcg = mem_cgroup_iter(NULL, NULL, NULL); do { @@ -287,13 +285,13 @@ static int expand_shrinker_maps(int new_id) ret = expand_one_shrinker_map(memcg, size, old_size); if (ret) { mem_cgroup_iter_break(NULL, memcg); - goto unlock; + goto out; } } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL); -unlock: +out: if (!ret) memcg_shrinker_map_size = size; - mutex_unlock(&memcg_shrinker_map_mutex); + return ret; } |