On Mon, 23 Feb 2015 19:14:55 -0500 Trond Myklebust
<trond.myklebust@xxxxxxxxxxxxxxx> wrote:
> If we're traversing a directory which contains a submounted filesystem,
> or one that has a referral, the NFS server that is processing the READDIR
> request will often return information for the underlying (mounted-on)
> directory. It may, or may not, also return filehandle information.
>
> If this happens, and the lookup in nfs_prime_dcache() returns the
> dentry for the submounted directory, the filehandle comparison will
> fail, and we call d_invalidate(). Post-commit 8ed936b5671bf
> ("vfs: Lazily remove mounts on unlinked files and directories."), this
> means the entire subtree is unmounted.
>
> The following minimal patch addresses this problem by punting on
> the invalidation if there is a submount.
>
> Kudos to Neil Brown <neilb@xxxxxxx> for having tracked down this
> issue (see link).
>
> Reported-by: Nix <nix@xxxxxxxxxxxxx>
> Link: http://lkml.kernel.org/r/87iofju9ht.fsf@xxxxxxxxxxxxxxxx
> Cc: stable@xxxxxxxxxxxxxxx # 3.18+
> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> ---
> fs/nfs/dir.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> index 9b0c55cb2a2e..0da617a61c0b 100644
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -479,6 +479,10 @@ void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry)
>
> dentry = d_lookup(parent, &filename);
> if (dentry != NULL) {
> + /* Is there a mountpoint here? If so, just exit */
> + if (!nfs_fsid_equal(&NFS_SB(dentry->d_sb)->fsid,
> + &entry->fattr->fsid))
> + goto out;
Surely we should only consider fattr->fsid if NFS_ATTR_FATTR_FSID is set.
In the case of the Linux NFSv3 server, if this were a mountpoint on the
server, then NFS_ATTR_FATTR_FSID will not be set (as the server returns
neither postop attrs nor filehandle).
I realise that this issue is addressed in the subsequent patch (3/3), but
that isn't tagged for -stable, and this is.
NeilBrown
> if (nfs_same_file(dentry, entry)) {
> nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
> status = nfs_refresh_inode(dentry->d_inode, entry->fattr);
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