On Tue, May 12, 2020 at 11:33:13AM -0400, Jeff Layton wrote: > On Tue, 2020-05-12 at 16:13 +0100, Luis Henriques wrote: > > Hi Jeff, > > > > I've been looking at xfstest generic/467 failure in cephfs, and I simply > > can not decide if it's a genuine bug on ceph kernel code. Since you've > > recently been touching the ceph_unlink code maybe you could help me > > understanding what's going on. > > > > generic/467 runs a couple of tests using src/open_by_handle, but the one > > failing can be summarized with the following: > > > > - get a handle to /cephfs/myfile using name_to_handle_at(2) > > - open(2) file /cephfs/myfile > > - unlink(2) /cephfs/myfile > > - drop caches > > - open_by_handle_at(2) => returns -ESTALE > > > > This test succeeds opening the handle with other (local) filesystems > > (maybe I should run it with other networked filesystem such as NFS). > > > > The -ESTALE is easy to trace to __fh_to_dentry, where inode->i_nlink is > > checked against 0. My question is: should we really be testing the > > i_nlink here? We dropped the name, but the file may still be there (as in > > this case). > > > > I guess I'm missing something, but hopefully you'll be able to shed some > > light on this. Thanks in advance for any help you may provide! > > Yeah, I took a brief look at this a while back and never got back to > looking at it again. I think cephfs's behavior is wrong here. We should > be able to look up an open-but-unlinked file by filehandle. > > That said those checks went in via commit 570df4e9c23f8, and it looks > like it was deliberately added to __fh_to_dentry. I'm unclear as to why. Right, I saw that commit too and that check came from the 'old' version of ceph_lookup_inode into the 'new' version of ceph_lookup_inode and into __fh_to_dentry. > It may be interesting to remove the i_nlink checks and see whether it > breaks anything? I've done that already and a very quick test didn't show anything. But it may break things a very subtle ways. I'll see if it's able to handle a full run of xfstests. Thanks for your hints, Jeff. I'll see if I can progress a bit further on this. Cheers, -- Luis
