Re: [PATCH] NFSD: Disallow layoutget during grace period

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2025-08-25 at 16:11 +0300, Sergey Bashirov wrote:
> When the server is recovering from a reboot and is in a grace period,
> any operation that may result in deletion or reallocation of block
> extents should not be allowed. See RFC 8881, section 18.43.3.
> 
> If multiple clients write data to the same file, rebooting the server
> during writing may result in file corruption. In the worst case, the
> exported XFS may also become corrupted. Observed this behavior while
> testing pNFS block volume setup.
> 
> Co-developed-by: Konstantin Evtushenko <koevtushenko@yandex.com>
> Signed-off-by: Konstantin Evtushenko <koevtushenko@yandex.com>
> Signed-off-by: Sergey Bashirov <sergeybashirov@gmail.com>
> ---
>  fs/nfsd/nfs4proc.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index bfebe6e25638a..3000b43be9221 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -2435,6 +2435,7 @@ static __be32
>  nfsd4_layoutget(struct svc_rqst *rqstp,
>  		struct nfsd4_compound_state *cstate, union nfsd4_op_u *u)
>  {
> +	struct net *net = SVC_NET(rqstp);
>  	struct nfsd4_layoutget *lgp = &u->layoutget;
>  	struct svc_fh *current_fh = &cstate->current_fh;
>  	const struct nfsd4_layout_ops *ops;
> @@ -2486,6 +2487,10 @@ nfsd4_layoutget(struct svc_rqst *rqstp,
>  	if (lgp->lg_seg.length == 0)
>  		goto out;
>  
> +	nfserr = nfserr_grace;
> +	if (locks_in_grace(net))
> +		goto out;
> +
>  	nfserr = nfsd4_preprocess_layout_stateid(rqstp, cstate, &lgp->lg_sid,
>  						true, lgp->lg_layout_type, &ls);
>  	if (nfserr) {


This seems like a reasonable thing to do, but I wonder if it makes
sense across all different pNFS layout types? This restriction is
definitely not needed for the (trivial) in-kernel flexfiles server, for
instance.

Maybe it'd be best to push this down into the individual layout drivers
and let them make the decision?  
-- 
Jeff Layton <jlayton@kernel.org>