Return-Path: Received: from mail-ww0-f44.google.com ([74.125.82.44]:47238 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759264Ab0KPGpH convert rfc822-to-8bit (ORCPT ); Tue, 16 Nov 2010 01:45:07 -0500 In-Reply-To: <20101115174837.GB10044@fieldses.org> References: <20101112184353.GA32745@fieldses.org> <20101115174837.GB10044@fieldses.org> Date: Tue, 16 Nov 2010 17:45:03 +1100 Message-ID: Subject: Re: lifetime of DCACHE_DISCONECTED dentries From: Nick Piggin To: "J. Bruce Fields" Cc: linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On Tue, Nov 16, 2010 at 4:48 AM, J. Bruce Fields wrote: > On Sat, Nov 13, 2010 at 10:53:12PM +1100, Nick Piggin wrote: >> On Sat, Nov 13, 2010 at 5:43 AM, J. Bruce Fields wrote: >> > ? ? ? ?- putfh: look up the filehandle. ?The only alias found for the >> > ? ? ? ? ?inode will be DCACHE_UNHASHED alias referenced by the filp >> > ? ? ? ? ?associated with the nfsd open. ?d_obtain_alias() doesn't like >> > ? ? ? ? ?this, so it creates a new DCACHE_DISCONECTED dentry and >> > ? ? ? ? ?returns that instead. >> >> This seems to be where the thing goes wrong. It isn't a hashed dentry at >> this point here, so d_obtain_alias should not be making one. > > Sounds sensible. ?(But can you think of any actual bugs that will result > from trying to add a new hashed dentry in this case?) Well, this one? :) >> I think the inode i_nlink games are much more appropriate on this side of >> the equation, rather than the dput side (after all, d_obtain_alias is setting >> up an alias for the inode). >> >> Can you even put the link check into __d_find_alias? >> >> - ? ? ? ? ? ? ? if (S_ISDIR(inode->i_mode) || !d_unhashed(alias)) { >> + ? ? ? ? ? ? ? if (S_ISDIR(inode->i_mode) || !inode->i_nlink || >> !d_unhashed(alias)) { >> >> Something like that? > > The immediate result of that would be for the close rpc (or any rpc's > sent after the file was unlinked) to fail with ESTALE. Why is that? Seems like it would be a bug, because a hashed dentry may be unhashed at any time concurrently to nfsd operation, so it should be able to tolerate that so long as it has a ref on the inode? > But nfsd already holds an open file in this case, and you could argue > that it should be using that from the start. Yes. > So, we could modify nfsd to add a hash mapping filehandles to the filp's > that it knows about, and have nfsd consult that hash before calling > dentry_to_fh. Could be an option. It would be a pity not just be able to use the alias list. What exactly goes wrong when it gets an unhashed alias back?