From: Tejun Heo Subject: Re: [PATCH 04/20] sysfs: Handle the general case of removing of directories with subdirectories Date: Thu, 21 May 2009 16:36:10 +0900 Message-ID: <4A15046A.10106@kernel.org> References: <1242865694-2100-1-git-send-email-ebiederm@xmission.com> <1242865694-2100-2-git-send-email-ebiederm@xmission.com> <1242865694-2100-3-git-send-email-ebiederm@xmission.com> <1242865694-2100-4-git-send-email-ebiederm@xmission.com> <4A14F356.3030501@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: Andrew Morton , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, Cornelia Huck , linux-fsdevel@vger.kernel.org, "Eric W. Biederman" To: "Eric W. Biederman" Return-path: Received: from hera.kernel.org ([140.211.167.34]:46883 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751105AbZEUHgd (ORCPT ); Thu, 21 May 2009 03:36:33 -0400 In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Eric W. Biederman wrote: >> I agree we should be heading this way but what happens to attributes >> or directories living below the subdirectories? If it's gonna handle >> recursive case, I think it better do it properly. I had patches of >> similar effect. > > I do handle it properly. sysfs_get_one finds the deepest child of the > first directory entry. Then I remove it. And I repeat until done. > > The locking is correct, something that is much more difficult to > tell with your version. Why? :-) > By grabbing and dropping the sysfs_mutex things are simpler, and they > get even simpler in future patches. > > Now looking at that code in detail there is a question of what happens if > we add a directory entry while we are recursively deleting a directory. > Neither your patch, my patch, nor the existing code handle that case > (assuming the sysfs_dirent) was looked up before it is removed from it's > parent directory. I expect another patch is called for to plug that > theoretical gap. > > I expect the way to close that hole is to have an extra flag that says > we are removing a directory entry and refuse to add if that flag is > set. > > I would prefer to only remove empty directories. But when I > instrumented things up I found cases where that does indeed happen. IIRC, my version did the whole thing while holding sysfs_mutex, so it's safe against such races. I can't really see why ops like this can't be atomic in sysfs. I don't really care how things are done but please make it atomic. Thanks. -- tejun