Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757285AbaDICjw (ORCPT ); Tue, 8 Apr 2014 22:39:52 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:55683 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756263AbaDICju (ORCPT ); Tue, 8 Apr 2014 22:39:50 -0400 Date: Wed, 9 Apr 2014 03:39:47 +0100 From: Al Viro To: "Eric W. Biederman" Cc: Linus Torvalds , "Serge E. Hallyn" , Linux-Fsdevel , Kernel Mailing List , Andy Lutomirski , Rob Landley , Miklos Szeredi , Christoph Hellwig , Karel Zak , "J. Bruce Fields" , Fengguang Wu Subject: Re: [GIT PULL] Detaching mounts on unlink for 3.15-rc1 Message-ID: <20140409023947.GY18016@ZenIV.linux.org.uk> References: <87a9kkax0j.fsf@xmission.com> <8761v7h2pt.fsf@tw-ebiederman.twitter.com> <87li281wx6.fsf_-_@xmission.com> <87ob28kqks.fsf_-_@xmission.com> <874n3n7czm.fsf_-_@xmission.com> <87wqezl5df.fsf_-_@x220.int.ebiederm.org> <20140409023027.GX18016@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140409023027.GX18016@ZenIV.linux.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 09, 2014 at 03:30:27AM +0100, Al Viro wrote: > > When renaming or unlinking directory entries that are not mountpoints > > no additional locks are taken so no performance differences can result, > > and my benchmark reflected that. > > It also means that d_invalidate() now might trigger fs shutdown. Which > has bloody huge stack footprint, for obvious reasons. And d_invalidate() > can be called with pretty deep stack - walk into wrong dentry while > resolving a deeply nested symlink and there you go... PS: I thought I actually replied with that point back a month or so ago, but having checked sent-mail... Looks like I had not. My deep apologies. FWIW, I think that overall this thing is a good idea, provided that we can live with semantics changes. The implementation is too optimistic, though - at the very least, we want this work done upon namespace_unlock() held back until we are not too deep in stack. task_work_add() fodder, perhaps? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/