sysfs: fix oops in directory removal.

If a file that doesn't exist was looked up in a directory, and that
directory is later removed, sysfs would reap the negative dentrys along 
with the valid ones.

Fix is to manually remove the dentrys from the parent's list under the 
dcache_lock, then check if they're valid with dget_locked(). 

This ensures all the dentrys are removed, valid and invalid, and we don't 
reap anything we shouldn't.

fs/sysfs/inode.c

@@ -98,10 +98,9 @@ static int sysfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t
 
 	if (!dentry->d_inode) {
 		inode = sysfs_get_inode(dir->i_sb, mode, dev);
-		if (inode) {
+		if (inode)
 			d_instantiate(dentry, inode);
-			dget(dentry);
-		} else
+		else
 			error = -ENOSPC;
 	} else
 		error = -EEXIST;
@@ -703,10 +702,6 @@ static void hash_and_remove(struct dentry * dir, const char * name)
 
 			pr_debug("sysfs: Removing %s (%d)\n", victim->d_name.name,
 				 atomic_read(&victim->d_count));
-			/**
-			 * Drop reference from initial get_dentry().
-			 */
-			dput(victim);
 		}
 		
 		/**
@@ -795,7 +790,7 @@ void sysfs_remove_link(struct kobject * kobj, char * name)
 
 void sysfs_remove_dir(struct kobject * kobj)
 {
-	struct list_head * node, * next;
+	struct list_head * node;
 	struct dentry * dentry = dget(kobj->dentry);
 	struct dentry * parent;
 
@@ -807,32 +802,31 @@ void sysfs_remove_dir(struct kobject * kobj)
 	down(&parent->d_inode->i_sem);
 	down(&dentry->d_inode->i_sem);
 
-	list_for_each_safe(node,next,&dentry->d_subdirs) {
-		struct dentry * d = dget(list_entry(node,struct dentry,d_child));
-		/** 
-		 * Make sure dentry is still there 
-		 */
-		pr_debug(" o %s: ",d->d_name.name);
-		if (d->d_inode) {
+	spin_lock(&dcache_lock);
+	node = dentry->d_subdirs.next;
+	while (node != &dentry->d_subdirs) {
+		struct dentry * d = list_entry(node,struct dentry,d_child);
+		list_del_init(node);
 
+		pr_debug(" o %s (%d): ",d->d_name.name,atomic_read(&d->d_count));
+		if (d->d_inode) {
+			d = dget_locked(d);
 			pr_debug("removing");
+
 			/**
 			 * Unlink and unhash.
 			 */
-			simple_unlink(dentry->d_inode,d);
+			spin_unlock(&dcache_lock);
 			d_delete(d);
-
-			/**
-			 * Drop reference from initial get_dentry().
-			 */
+			simple_unlink(dentry->d_inode,d);
 			dput(d);
+			spin_lock(&dcache_lock);
 		}
-		pr_debug(" done (%d)\n",atomic_read(&d->d_count));
-		/**
-		 * drop reference from dget() above.
-		 */
-		dput(d);
+		pr_debug(" done\n");
+
+		node = dentry->d_subdirs.next;
 	}
+	spin_unlock(&dcache_lock);
 
 	up(&dentry->d_inode->i_sem);
 	d_invalidate(dentry);