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

Qi Zheng
2023-08-07T11:11:21Z

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@bytedance.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
---
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