[PATCH] mm: shmem: assign a lock class to the unused huge shrinklist

[Qi Zheng <qi.zheng@linux.dev>]

From: Qi Zheng <zhengqi.arch@bytedance.com>

The unused huge shrinklist shares the default list_lru lock class with the
dentry LRU.  Although they use distinct lock instances, lockdep conflates
their dependencies and reports a circular locking dependency:

	WARNING: possible circular locking dependency detected

Give the unused huge shrinklist a dedicated lock class to fix this
false-positive lockdep warning.

Fixes: b9b1861d4f7a ("mm: shmem: make unused huge shrinker memcg aware")
Reported-by: kernel test robot <yi1.lai@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202610091403.d1d8080b-lkp@intel.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 mm/shmem.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 5a9bcc7c66926..a6e3c9c7f72da 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -5164,6 +5164,9 @@ static const struct dentry_operations shmem_ci_dentry_ops = {
 
 static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
 {
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	static struct lock_class_key shmem_unused_huge_lock_key;
+#endif
 	struct shmem_options *ctx = fc->fs_private;
 	struct inode *inode;
 	struct shmem_sb_info *sbinfo;
@@ -5243,7 +5246,8 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
 		goto failed;
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (list_lru_init_memcg(&sbinfo->shrinklist, sb->s_shrink))
+	if (list_lru_init_memcg_key(&sbinfo->shrinklist, sb->s_shrink,
+				    &shmem_unused_huge_lock_key))
 		goto failed;
 #endif
 
-- 
2.54.0