From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: lifetime of DCACHE_DISCONECTED dentries Date: Tue, 30 Nov 2010 12:00:16 +1100 Message-ID: References: <20101112184353.GA32745@fieldses.org> <20101115174837.GB10044@fieldses.org> <20101129193248.GA9897@fieldses.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "J. Bruce Fields" Return-path: In-Reply-To: <20101129193248.GA9897-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org> Sender: linux-nfs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org 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 wro= te: >> > 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: >> > >> >>> > =A0 =A0 =A0 =A0- putfh: look up the filehandle. =A0The only al= ias found for the >> >>> > =A0 =A0 =A0 =A0 =A0inode will be DCACHE_UNHASHED alias referen= ced by the filp >> >>> > =A0 =A0 =A0 =A0 =A0associated with the nfsd open. =A0d_obtain_= alias() doesn't like >> >>> > =A0 =A0 =A0 =A0 =A0this, so it creates a new DCACHE_DISCONECTE= D dentry and >> >>> > =A0 =A0 =A0 =A0 =A0returns that instead. >> >>> >> >>> This seems to be where the thing goes wrong. It isn't a hashed d= entry at >> >>> this point here, so d_obtain_alias should not be making one. >> >> >> >> Sounds sensible. =A0(But can you think of any actual bugs that wi= ll 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 thi= s side of >> >>> the equation, rather than the dput side (after all, d_obtain_ali= as is setting >> >>> up an alias for the inode). >> >>> >> >>> Can you even put the link check into __d_find_alias? >> >>> >> >>> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (S_ISDIR(inode->i_mode) || !d_u= nhashed(alias)) { >> >>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (S_ISDIR(inode->i_mode) || !ino= de->i_nlink || >> >>> !d_unhashed(alias)) { >> >>> >> >>> Something like that? >> >> >> >> The immediate result of that would be for the close rpc (or any r= pc'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 shou= ld 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 se= ems >> 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 alia= s > in the i_nlink =3D=3D 0 case! > > Yes, agreed, that should solve my problem. OK, good. > But what's the reason for the d_unhashed() check now? =A0Could 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. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html