[PATCH v5 1/3] kernfs: Don't set_nlink for directories being removed

["T.J. Mercier" <tjmercier@google.com>]

If a directory is already in the process of removal its i_nlink count
becomes irrelevant because its contents are also about to be removed and
any pending filesystem operations on it or its contents will soon start
to fail. So we can avoid setting it for directories already flagged for
removal.

This avoids a race in the next patch, which adds clearing of the i_nlink
count for kernfs nodes being removed to support inotify delete events.

Use protection from the kernfs_iattr_rwsem to avoid adding more
contention to the kernfs_rwsem for calls to kernfs_refresh_inode.

Signed-off-by: T.J. Mercier <tjmercier@google.com>
---
 fs/kernfs/dir.c   | 2 ++
 fs/kernfs/inode.c | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 29baeeb97871..5b6ce2351a53 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -1491,12 +1491,14 @@ static void __kernfs_remove(struct kernfs_node *kn)
 	pr_debug("kernfs %s: removing\n", kernfs_rcu_name(kn));
 
 	/* prevent new usage by marking all nodes removing and deactivating */
+	down_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
 	pos = NULL;
 	while ((pos = kernfs_next_descendant_post(pos, kn))) {
 		pos->flags |= KERNFS_REMOVING;
 		if (kernfs_active(pos))
 			atomic_add(KN_DEACTIVATED_BIAS, &pos->active);
 	}
+	up_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
 
 	/* deactivate and unlink the subtree node-by-node */
 	do {
diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index a36aaee98dce..afdc4021e81a 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -178,7 +178,7 @@ static void kernfs_refresh_inode(struct kernfs_node *kn, struct inode *inode)
 		 */
 		set_inode_attr(inode, attrs);
 
-	if (kernfs_type(kn) == KERNFS_DIR)
+	if (kernfs_type(kn) == KERNFS_DIR && !(kn->flags & KERNFS_REMOVING))
 		set_nlink(inode, kn->dir.subdirs + 2);
 }
 
-- 
2.53.0.414.gf7e9f6c205-goog