4 files changed, 18 insertions, 0 deletions
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 741dc0b6931f..c851158324e2 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -151,6 +151,7 @@ int ovl_want_write(struct dentry *dentry);
 void ovl_drop_write(struct dentry *dentry);
 struct dentry *ovl_workdir(struct dentry *dentry);
 const struct cred *ovl_override_creds(struct super_block *sb);
+struct super_block *ovl_same_sb(struct super_block *sb);
 struct ovl_entry *ovl_alloc_entry(unsigned int numlower);
 bool ovl_dentry_remote(struct dentry *dentry);
 bool ovl_dentry_weird(struct dentry *dentry);
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 59614faa14c3..b2023ddb8532 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -29,6 +29,8 @@ struct ovl_fs {
 	const struct cred *creator_cred;
 	bool tmpfile;
 	wait_queue_head_t copyup_wq;
+	/* sb common to all layers */
+	struct super_block *same_sb;
 };
 
 /* private information held for every overlayfs dentry */
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 6faefa54cb5e..9828b7de8999 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -914,11 +914,19 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 
 		ufs->lower_mnt[ufs->numlower] = mnt;
 		ufs->numlower++;
+
+		/* Check if all lower layers are on same sb */
+		if (i == 0)
+			ufs->same_sb = mnt->mnt_sb;
+		else if (ufs->same_sb != mnt->mnt_sb)
+			ufs->same_sb = NULL;
 	}
 
 	/* If the upper fs is nonexistent, we mark overlayfs r/o too */
 	if (!ufs->upper_mnt)
 		sb->s_flags |= MS_RDONLY;
+	else if (ufs->upper_mnt->mnt_sb != ufs->same_sb)
+		ufs->same_sb = NULL;
 
 	if (remote)
 		sb->s_d_op = &ovl_reval_dentry_operations;
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 35b8959db5ee..2bd4c264ccbe 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -41,6 +41,13 @@ const struct cred *ovl_override_creds(struct super_block *sb)
 	return override_creds(ofs->creator_cred);
 }
 
+struct super_block *ovl_same_sb(struct super_block *sb)
+{
+	struct ovl_fs *ofs = sb->s_fs_info;
+
+	return ofs->same_sb;
+}
+
 struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
 {
 	size_t size = offsetof(struct ovl_entry, lowerstack[numlower]);