Re: 2.6.24-rc2 XFS nfsd hang

J. Bruce Fields
2007-11-14T17:39:42Z

On Wed, Nov 14, 2007 at 03:29:52PM +0000, Christoph Hellwig wrote:
> On Tue, Nov 13, 2007 at 11:04:00PM -0800, Chris Wedgwood wrote:
> > With 2.6.24-rc2 (amd64) I sometimes (usually but perhaps not always)
> > see a hang when accessing some NFS exported XFS filesystems. Local
> > access to these filesystems ahead of time works without problems.
> >
> > This does not occur with 2.6.23.1. The filesystem does not appear to
> > be corrupt.
> >
>
> > [ 1462.911360] ffffffff80744020 ffffffff80746dc0 ffff81010129c140 ffff8101000ad100
> > [ 1462.911391] Call Trace:
> > [ 1462.911417] [<ffffffff8052e638>] __down+0xe9/0x101
> > [ 1462.911437] [<ffffffff8022cc80>] default_wake_function+0x0/0xe
> > [ 1462.911458] [<ffffffff8052e275>] __down_failed+0x35/0x3a
> > [ 1462.911480] [<ffffffff8035ac25>] _xfs_buf_find+0x84/0x24d
> > [ 1462.911501] [<ffffffff8035ad34>] _xfs_buf_find+0x193/0x24d
> > [ 1462.911522] [<ffffffff803599b1>] xfs_buf_lock+0x43/0x45
>
> this is bp->b_sema which lookup wants.
>
> > [ 1462.915534] [<ffffffff8032b6da>] xfs_readdir+0x91/0xb6
> > [ 1462.915557] [<ffffffff8030415b>] nfs3svc_encode_entry_plus+0x0/0x13
> > [ 1462.915579] [<ffffffff8035be9d>] xfs_file_readdir+0x31/0x40
> > [ 1462.915599] [<ffffffff8028c9f8>] vfs_readdir+0x61/0x93
> > [ 1462.915619] [<ffffffff8030415b>] nfs3svc_encode_entry_plus+0x0/0x13
> > [ 1462.915642] [<ffffffff802fc78e>] nfsd_readdir+0x6d/0xc5
>
> and this is the nasty nfsd case where a filldir callback calls back
> into lookup. I suspect we're somehow holding b_sema already. Previously
> this was okay because we weren't inside the actualy readdir code when
> calling filldir but operate on a copy of the data.
>
> This gem has bitten other filesystem before, I'll see if I can find a
> way around it.

This must have come up before; feel free to remind me: is there any way
to make the interface easier to use? (E.g. would it help if the filldir
callback could be passed a dentry?)

--b.