[PATCH v7 07/12] kernfs: hold kernfs_iattr_rwsem when initializing a new inode

[Jori Koolstra]

kernfs_refresh_inode() copies the uid, gid, timestamps and nlink of a
kernfs_node into its VFS inode. Since commit 9caf69614225 ("kernfs:
Introduce separate rwsem to protect inode attributes.") these are
protected by kernfs_iattr_rwsem.

kernfs_init_inode() calls kernfs_refresh_inode(), but was not converted.
Its callers in turn hold kernfs_rwsem (kernfs_iop_lookup(),
kernfs_fill_super()) or no lock at all (__kernfs_fh_to_dentry()),
neither of which excludes a concurrent
kernfs_setattr()/kernfs_iop_setattr().

Take kernfs_iattr_rwsem for reading around the refresh in
kernfs_init_inode(). This nests inside kernfs_rwsem, which matches
kernfs_link_sibling() and kernfs_unlink_sibling().

Also, kernfs_get_inode() then does not need to hold kernfs_rwsem, so
drop it from kernfs_fill_super().

Fixes: 9caf69614225 ("kernfs: Introduce separate rwsem to protect inode attributes.")
Signed-off-by: Jori Koolstra <jkoolstra@xxxxxxxxx>
---
 fs/kernfs/inode.c | 3 ++-
 fs/kernfs/mount.c | 3 ---
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index abb286bc3474..83f2007498db 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -204,7 +204,8 @@ static void kernfs_init_inode(struct kernfs_node *kn, struct inode *inode)
 	inode->i_generation = kernfs_gen(kn);
 
 	set_default_inode_attr(inode, kn->mode);
-	kernfs_refresh_inode(kn, inode);
+	scoped_guard(rwsem_read, &kernfs_root(kn)->kernfs_iattr_rwsem)
+		kernfs_refresh_inode(kn, inode);
 
 	/* initialize inode according to type */
 	switch (kernfs_type(kn)) {
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index a57399021c8b..202a5ca2bd34 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -283,7 +283,6 @@ struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
 static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
 {
 	struct kernfs_super_info *info = kernfs_info(sb);
-	struct kernfs_root *kf_root = kfc->root;
 	struct inode *inode;
 	struct dentry *root;
 
@@ -304,9 +303,7 @@ static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *k
 	sb->s_shrink->seeks = 0;
 
 	/* get root inode, initialize and unlock it */
-	down_read(&kf_root->kernfs_rwsem);
 	inode = kernfs_get_inode(sb, info->root->kn);
-	up_read(&kf_root->kernfs_rwsem);
 	if (!inode) {
 		pr_debug("kernfs: could not get root inode\n");
 		return -ENOMEM;
-- 
2.56.0