From mboxrd@z Thu Jan 1 00:00:00 1970 From: "J. Bruce Fields" Subject: Re: lifetime of DCACHE_DISCONECTED dentries Date: Tue, 30 Nov 2010 13:39:41 -0500 Message-ID: <20101130183941.GB29091@fieldses.org> References: <20101112184353.GA32745@fieldses.org> <20101115174837.GB10044@fieldses.org> <20101129193248.GA9897@fieldses.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Nick Piggin Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-nfs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org 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 w= rote: > >> > 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: > >> > > >> >>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0- putfh: look up the filehandle. = =C2=A0The only alias found for the > >> >>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0inode will be DCACHE_UNHAS= HED alias referenced by the filp > >> >>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0associated with the nfsd o= pen. =C2=A0d_obtain_alias() doesn't like > >> >>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0this, so it creates a new = DCACHE_DISCONECTED dentry and > >> >>> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0returns 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. =C2=A0(But can you think of any actual bugs th= at 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 t= his side of > >> >>> the equation, rather than the dput side (after all, d_obtain_a= lias is setting > >> >>> up an alias for the inode). > >> >>> > >> >>> Can you even put the link check into __d_find_alias? > >> >>> > >> >>> - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 if (S_ISDIR= (inode->i_mode) || !d_unhashed(alias)) { > >> >>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 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 dent= ry may > >> > be unhashed at any time concurrently to nfsd operation, so it sh= ould 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 ino= de). > > > > 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 al= ias > > in the i_nlink =3D=3D 0 case! > > > > Yes, agreed, that should solve my problem. >=20 > OK, good. >=20 > > But what's the reason for the d_unhashed() check now? =C2=A0Could w= e get rid > > of it entirely? >=20 > Well when the inode still has links I think we actually do want any n= ew > 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 t= o someone? --b. -- 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