Return-Path: Received: from fieldses.org ([174.143.236.118]:46645 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751168Ab0K2Tct (ORCPT ); Mon, 29 Nov 2010 14:32:49 -0500 Date: Mon, 29 Nov 2010 14:32:48 -0500 From: "J. Bruce Fields" To: Nick Piggin Cc: linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: lifetime of DCACHE_DISCONECTED dentries Message-ID: <20101129193248.GA9897@fieldses.org> References: <20101112184353.GA32745@fieldses.org> <20101115174837.GB10044@fieldses.org> Content-Type: text/plain; charset=utf-8 In-Reply-To: Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On Mon, Nov 29, 2010 at 02:56:22PM +1100, Nick Piggin wrote: > On Tue, Nov 16, 2010 at 5:45 PM, Nick Piggin wrote: > > 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? > > Ping? Did you work out why nfs fails with ESTALE in that case? It seems > to work in my testing (and do the right thing with freeing the inode). Bah, sorry, I read too quickly, got the sense of the test backwards, and thought you were suggesting __d_find_alias() shouldn't return an alias in the i_nlink == 0 case! Yes, agreed, that should solve my problem. But what's the reason for the d_unhashed() check now? Could we get rid of it entirely? --b.