Re: 2.6.24-rc2 XFS nfsd hang

Christoph Hellwig
2007-11-14T15:30:17Z

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.