Return-Path: Received: from fieldses.org ([174.143.236.118]:34722 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752193Ab0K3Sjn (ORCPT ); Tue, 30 Nov 2010 13:39:43 -0500 Date: Tue, 30 Nov 2010 13:39:41 -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: <20101130183941.GB29091@fieldses.org> References: <20101112184353.GA32745@fieldses.org> <20101115174837.GB10044@fieldses.org> <20101129193248.GA9897@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 Tue, Nov 30, 2010 at 12:00:16PM +1100, Nick Piggin wrote: > On Tue, Nov 30, 2010 at 6:32 AM, J. Bruce Fields wrote: > > 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. > > OK, good. > > > But what's the reason for the d_unhashed() check now?  Could we get rid > > of it entirely? > > Well when the inode still has links I think we actually do want any new > references to go to hashed dentries. Definitely for d_splice_alias. OK, makes sense. Should we stick a changelog on it and pass it along to someone? --b.