configfs: provide exclusion between IO and removals

Make sure that attribute methods are not called after the item
has been removed from the tree.  To do so, we
	* at the point of no return in removals, grab ->frag_sem
exclusive and mark the fragment dead.
	* call the methods of attributes with ->frag_sem taken
shared and only after having verified that the fragment is still
alive.

	The main benefit is for method instances - they are
guaranteed that the objects they are accessing *and* all ancestors
are still there.  Another win is that we don't need to bother
with extra refcount on config_item when opening a file -
the item will be alive for as long as it stays in the tree, and
we won't touch it/attributes/any associated data after it's
been removed from the tree.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>

1 files changed, 23 insertions, 0 deletions

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 1df65c2440da..79fc25aaa8cd 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -1461,6 +1461,7 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
 	struct config_item *item;
 	struct configfs_subsystem *subsys;
 	struct configfs_dirent *sd;
+	struct configfs_fragment *frag;
 	struct module *subsys_owner = NULL, *dead_item_owner = NULL;
 	int ret;
 
@@ -1518,6 +1519,16 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
 		}
 	} while (ret == -EAGAIN);
 
+	frag = sd->s_frag;
+	if (down_write_killable(&frag->frag_sem)) {
+		spin_lock(&configfs_dirent_lock);
+		configfs_detach_rollback(dentry);
+		spin_unlock(&configfs_dirent_lock);
+		return -EINTR;
+	}
+	frag->frag_dead = true;
+	up_write(&frag->frag_sem);
+
 	/* Get a working ref for the duration of this function */
 	item = configfs_get_config_item(dentry);
 
@@ -1821,6 +1832,12 @@ void configfs_unregister_group(struct config_group *group)
 	struct configfs_subsystem *subsys = group->cg_subsys;
 	struct dentry *dentry = group->cg_item.ci_dentry;
 	struct dentry *parent = group->cg_item.ci_parent->ci_dentry;
+	struct configfs_dirent *sd = dentry->d_fsdata;
+	struct configfs_fragment *frag = sd->s_frag;
+
+	down_write(&frag->frag_sem);
+	frag->frag_dead = true;
+	up_write(&frag->frag_sem);
 
 	inode_lock_nested(d_inode(parent), I_MUTEX_PARENT);
 	spin_lock(&configfs_dirent_lock);
@@ -1947,12 +1964,18 @@ void configfs_unregister_subsystem(struct configfs_subsystem *subsys)
 	struct config_group *group = &subsys->su_group;
 	struct dentry *dentry = group->cg_item.ci_dentry;
 	struct dentry *root = dentry->d_sb->s_root;
+	struct configfs_dirent *sd = dentry->d_fsdata;
+	struct configfs_fragment *frag = sd->s_frag;
 
 	if (dentry->d_parent != root) {
 		pr_err("Tried to unregister non-subsystem!\n");
 		return;
 	}
 
+	down_write(&frag->frag_sem);
+	frag->frag_dead = true;
+	up_write(&frag->frag_sem);
+
 	inode_lock_nested(d_inode(root),
 			  I_MUTEX_PARENT);
 	inode_lock_nested(d_inode(dentry), I_MUTEX_CHILD);