From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f48.google.com (mail-pa0-f48.google.com [209.85.220.48]) by kanga.kvack.org (Postfix) with ESMTP id B8F996B0253 for ; Tue, 25 Aug 2015 17:09:00 -0400 (EDT) Received: by pacti10 with SMTP id ti10so62700052pac.0 for ; Tue, 25 Aug 2015 14:09:00 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id ki6si489292pdb.252.2015.08.25.14.08.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 25 Aug 2015 14:08:59 -0700 (PDT) Date: Tue, 25 Aug 2015 14:08:58 -0700 From: Andrew Morton Subject: Re: [PATCH] mm/backing-dev: Check return value of the debugfs_create_dir() Message-Id: <20150825140858.8185db77fed42cf5df5faeb5@linux-foundation.org> In-Reply-To: <1440489263-3547-1-git-send-email-kuleshovmail@gmail.com> References: <1440489263-3547-1-git-send-email-kuleshovmail@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Alexander Kuleshov Cc: Tejun Heo , Jan Kara , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue, 25 Aug 2015 13:54:23 +0600 Alexander Kuleshov wrote: > The debugfs_create_dir() function may fail and return error. If the > root directory not created, we can't create anything inside it. This > patch adds check for this case. > > ... > > --- a/mm/backing-dev.c > +++ b/mm/backing-dev.c > @@ -117,15 +117,21 @@ static const struct file_operations bdi_debug_stats_fops = { > > static void bdi_debug_register(struct backing_dev_info *bdi, const char *name) > { > - bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root); > - bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir, > - bdi, &bdi_debug_stats_fops); > + if (bdi_debug_root) { > + bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root); > + if (bdi->debug_dir) > + bdi->debug_stats = debugfs_create_file("stats", 0444, > + bdi->debug_dir, bdi, > + &bdi_debug_stats_fops); > + } If debugfs_create_dir() fails, debugfs_create_file() will go ahead and attempt to create the debugfs file in the debugfs root directory: : static struct dentry *start_creating(const char *name, struct dentry *parent) : { : ... : /* If the parent is not specified, we create it in the root. : * We need the root dentry to do this, which is in the super : * block. A pointer to that is in the struct vfsmount that we : * have around. : */ : if (!parent) : parent = debugfs_mount->mnt_root; I'm not sure that this is very useful behaviour, and putting the files in the wrong place is a very obscure way of informing the user that debugfs_create_dir() failed :( I don't think it's worth making little changes such as this - handling debugfs failures needs a deeper rethink. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org