[v6,44/45] mm: shrinker: hold write lock to reparent shrinker nr_deferred

Commit Message

Qi Zheng Sept. 11, 2023, 9:44 a.m. UTC

For now, reparent_shrinker_deferred() is the only holder of read lock of
shrinker_rwsem. And it already holds the global cgroup_mutex, so it will
not be called in parallel.

Therefore, in order to convert shrinker_rwsem to shrinker_mutex later,
here we change to hold the write lock of shrinker_rwsem to reparent.

Signed-off-by: Qi Zheng <[e-mail]>
---
 mm/shrinker.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Muchun Song Sept. 18, 2023, 7:17 a.m. UTC | #1

> On Sep 11, 2023, at 17:44, Qi Zheng <[e-mail]> wrote:
> 
> For now, reparent_shrinker_deferred() is the only holder of read lock of
> shrinker_rwsem. And it already holds the global cgroup_mutex, so it will
> not be called in parallel.
> 
> Therefore, in order to convert shrinker_rwsem to shrinker_mutex later,
> here we change to hold the write lock of shrinker_rwsem to reparent.
> 
> Signed-off-by: Qi Zheng <[e-mail]>

Reviewed-by: Muchun Song <[e-mail]>

Thanks.

Patch

diff --git a/mm/shrinker.c b/mm/shrinker.c
index ad64cac5248c..471c07d75c4a 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -292,7 +292,7 @@  void reparent_shrinker_deferred(struct mem_cgroup *memcg)
 		parent = root_mem_cgroup;
 
 	/* Prevent from concurrent shrinker_info expand */
-	down_read(&shrinker_rwsem);
+	down_write(&shrinker_rwsem);
 	for_each_node(nid) {
 		child_info = shrinker_info_protected(memcg, nid);
 		parent_info = shrinker_info_protected(parent, nid);
@@ -305,7 +305,7 @@  void reparent_shrinker_deferred(struct mem_cgroup *memcg)
 			}
 		}
 	}
-	up_read(&shrinker_rwsem);
+	up_write(&shrinker_rwsem);
 }
 #else
 static int shrinker_memcg_alloc(struct shrinker *shrinker)