ovl: lockdep annotate of nested stacked overlayfs inode lock (b1eaa950) · Commits · 戴 / test

An overlayfs instance can be the lower layer of another overlayfs instance. This setup triggers a lockdep splat of possible recursive locking of sb->s_type->i_mutex_key in iterate_dir(). Trimmed snip: [ INFO: possible recursive locking detected ] bash/2468 is trying to acquire lock: &sb->s_type->i_mutex_key#14, at: iterate_dir+0x7d/0x15c but task is already holding lock: &sb->s_type->i_mutex_key#14, at: iterate_dir+0x7d/0x15c One problem observed with this splat is that ovl_new_inode() does not call lockdep_annotate_inode_mutex_key() to annotate the dir inode lock as &sb->s_type->i_mutex_dir_key like other fs do. The other problem is that the 2 nested levels of overlayfs inode lock are annotated using the same key, which is the cause of the false positive lockdep warning. Fix this by annotating overlayfs inode lock in ovl_fill_inode() according to stack level of the super block instance and use different key for dir vs. non-dir like other fs do. Here is an edited snip from /proc/lockdep_chains after iterate_dir() of nested overlayfs: [...] &ovl_i_mutex_dir_key[depth] (stack_depth=2) [...] &ovl_i_mutex_dir_key[depth]#2 (stack_depth=1) [...] &type->i_mutex_dir_key (stack_depth=0) Signed-off-by:

Amir Goldstein <amir73il@gmail.com> Signed-off-by:

Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/inode.c

+37 −0

Original line number	Diff line number	Diff line
		@@ -303,6 +303,41 @@ static const struct inode_operations ovl_symlink_inode_operations = {
		.update_time = ovl_update_time,
		};

		/*
		* It is possible to stack overlayfs instance on top of another
		* overlayfs instance as lower layer. We need to annonate the
		* stackable i_mutex locks according to stack level of the super
		* block instance. An overlayfs instance can never be in stack
		* depth 0 (there is always a real fs below it). An overlayfs
		* inode lock will use the lockdep annotaion ovl_i_mutex_key[depth].
		*
		* For example, here is a snip from /proc/lockdep_chains after
		* dir_iterate of nested overlayfs:
		*
		* [...] &ovl_i_mutex_dir_key[depth] (stack_depth=2)
		* [...] &ovl_i_mutex_dir_key[depth]#2 (stack_depth=1)
		* [...] &type->i_mutex_dir_key (stack_depth=0)
		*/
		#define OVL_MAX_NESTING FILESYSTEM_MAX_STACK_DEPTH

		static inline void ovl_lockdep_annotate_inode_mutex_key(struct inode *inode)
		{
		#ifdef CONFIG_LOCKDEP
		static struct lock_class_key ovl_i_mutex_key[OVL_MAX_NESTING];
		static struct lock_class_key ovl_i_mutex_dir_key[OVL_MAX_NESTING];

		int depth = inode->i_sb->s_stack_depth - 1;

		if (WARN_ON_ONCE(depth < 0 \|\| depth >= OVL_MAX_NESTING))
		depth = 0;

		if (S_ISDIR(inode->i_mode))
		lockdep_set_class(&inode->i_rwsem, &ovl_i_mutex_dir_key[depth]);
		else
		lockdep_set_class(&inode->i_rwsem, &ovl_i_mutex_key[depth]);
		#endif
		}

		static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev)
		{
		inode->i_ino = get_next_ino();
		@@ -312,6 +347,8 @@ static void ovl_fill_inode(struct inode *inode, umode_t mode, dev_t rdev)
		inode->i_acl = inode->i_default_acl = ACL_DONT_CACHE;
		#endif

		ovl_lockdep_annotate_inode_mutex_key(inode);

		switch (mode & S_IFMT) {
		case S_IFREG:
		inode->i_op = &ovl_file_inode_operations;

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