sysfs: convert BUG_ON to WARN_ON

It's rude to crash the system just because the developer did something
wrong, as it prevents them from usually even seeing what went wrong.

So convert the few BUG_ON() calls that have snuck into the sysfs code
over the years to WARN_ON() to make it more "friendly". All of these
are able to be recovered from, so it makes no sense to crash.

Reported-by: Linus Torvalds <[e-mail]>
Reviewed-by: Rafael J. Wysocki <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

fs/sysfs/dir.c

···
 	kuid_t uid;
 	kgid_t gid;
 
-	BUG_ON(!kobj);
+	if (WARN_ON(!kobj))
+		return -EINVAL;
 
 	if (kobj->parent)
 		parent = kobj->parent->sd;

fs/sysfs/file.c

···
 	kuid_t uid;
 	kgid_t gid;
 
-	BUG_ON(!kobj || !kobj->sd || !attr);
+	if (WARN_ON(!kobj || !kobj->sd || !attr))
+		return -EINVAL;
 
 	kobject_get_ownership(kobj, &uid, &gid);
 	return sysfs_add_file_mode_ns(kobj->sd, attr, false, attr->mode,
···
 	kuid_t uid;
 	kgid_t gid;
 
-	BUG_ON(!kobj || !kobj->sd || !attr);
+	if (WARN_ON(!kobj || !kobj->sd || !attr))
+		return -EINVAL;
 
 	kobject_get_ownership(kobj, &uid, &gid);
 	return sysfs_add_file_mode_ns(kobj->sd, &attr->attr, true,

fs/sysfs/group.c

···
 	kgid_t gid;
 	int error;
 
-	BUG_ON(!kobj || (!update && !kobj->sd));
+	if (WARN_ON(!kobj || (!update && !kobj->sd)))
+		return -EINVAL;
 
 	/* Updates may happen before the object has been instantiated */
 	if (unlikely(update && !kobj->sd))

fs/sysfs/symlink.c

···
 {
 	struct kernfs_node *kn, *target = NULL;
 
-	BUG_ON(!name || !parent);
+	if (WARN_ON(!name || !parent))
+		return -EINVAL;
 
 	/*
 	 * We don't own @target_kobj and it may be removed at any time.