[PATCH v4 03/48] mm: shrinker: remove redundant shrinker_rwsem in debugfs operations

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

The debugfs_remove_recursive() will wait for debugfs_file_put() to return,
so the shrinker will not be freed when doing debugfs operations (such as
shrinker_debugfs_count_show() and shrinker_debugfs_scan_write()), so there
is no need to hold shrinker_rwsem during debugfs operations.

Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 mm/shrinker_debug.c | 16 +---------------
 1 file changed, 1 insertion(+), 15 deletions(-)

diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c
index 3ab53fad8876..61702bdc1af4 100644
--- a/mm/shrinker_debug.c
+++ b/mm/shrinker_debug.c
@@ -49,17 +49,12 @@ static int shrinker_debugfs_count_show(struct seq_file *m, 
void *v)
        struct mem_cgroup *memcg;
        unsigned long total;
        bool memcg_aware;
-       int ret, nid;
+       int ret = 0, nid;
 
        count_per_node = kcalloc(nr_node_ids, sizeof(unsigned long), 
GFP_KERNEL);
        if (!count_per_node)
                return -ENOMEM;
 
-       ret = down_read_killable(&shrinker_rwsem);
-       if (ret) {
-               kfree(count_per_node);
-               return ret;
-       }
        rcu_read_lock();
 
        memcg_aware = shrinker->flags & SHRINKER_MEMCG_AWARE;
@@ -92,7 +87,6 @@ static int shrinker_debugfs_count_show(struct seq_file *m, 
void *v)
        } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
 
        rcu_read_unlock();
-       up_read(&shrinker_rwsem);
 
        kfree(count_per_node);
        return ret;
@@ -117,7 +111,6 @@ static ssize_t shrinker_debugfs_scan_write(struct file 
*file,
        struct mem_cgroup *memcg = NULL;
        int nid;
        char kbuf[72];
-       ssize_t ret;
 
        read_len = size < (sizeof(kbuf) - 1) ? size : (sizeof(kbuf) - 1);
        if (copy_from_user(kbuf, buf, read_len))
@@ -146,12 +139,6 @@ static ssize_t shrinker_debugfs_scan_write(struct file 
*file,
                return -EINVAL;
        }
 
-       ret = down_read_killable(&shrinker_rwsem);
-       if (ret) {
-               mem_cgroup_put(memcg);
-               return ret;
-       }
-
        sc.nid = nid;
        sc.memcg = memcg;
        sc.nr_to_scan = nr_to_scan;
@@ -159,7 +146,6 @@ static ssize_t shrinker_debugfs_scan_write(struct file 
*file,
 
        shrinker->scan_objects(shrinker, &sc);
 
-       up_read(&shrinker_rwsem);
        mem_cgroup_put(memcg);
 
        return size;
-- 
2.30.2