[RFC PATCH] NFSD: Skip sending CB_RECALL_ANY when the backchannel isn't up

[RFC PATCH] NFSD: Skip sending CB_RECALL_ANY when the backchannel isn't up

[cel]

From: Chuck Lever <chuck.lever@oracle.com>

NFSD sends CB_RECALL_ANY to clients when the server is low on
memory or that client has a large number of delegations outstanding.

We've seen cases where NFSD attempts to send CB_RECALL_ANY requests
to disconnected clients, and gets confused. These calls never go
anywhere if a backchannel transport to the target client isn't
available. Before the server can send any backchannel operation, the
client has to connect first and then do a BIND_CONN_TO_SESSION.

This patch doesn't address the root cause of the confusion, but
there's no need to queue up these optional operations if they can't
go anywhere.

Fixes: 44df6f439a17 ("NFSD: add delegation reaper to react to low memory condition")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/nfs4state.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index b7a0cfd05401..9ef32b19198c 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -6867,7 +6867,8 @@ deleg_reaper(struct nfsd_net *nn)
 				clp->cl_ra_time < 5)) {
 			continue;
 		}
-		list_add(&clp->cl_ra_cblist, &cblist);
+		if (clp->cl_cb_state == NFSD4_CB_UP)
+			list_add(&clp->cl_ra_cblist, &cblist);
 
 		/* release in nfsd4_cb_recall_any_release */
 		kref_get(&clp->cl_nfsdfs.cl_ref);
-- 
2.47.0

Re: [RFC PATCH] NFSD: Skip sending CB_RECALL_ANY when the backchannel isn't up

[Jeff Layton]

On Tue, 2025-01-14 at 17:09 -0500, cel@kernel.org wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> NFSD sends CB_RECALL_ANY to clients when the server is low on
> memory or that client has a large number of delegations outstanding.
> 
> We've seen cases where NFSD attempts to send CB_RECALL_ANY requests
> to disconnected clients, and gets confused. These calls never go
> anywhere if a backchannel transport to the target client isn't
> available. Before the server can send any backchannel operation, the
> client has to connect first and then do a BIND_CONN_TO_SESSION.
> 
> This patch doesn't address the root cause of the confusion, but
> there's no need to queue up these optional operations if they can't
> go anywhere.
> 
> Fixes: 44df6f439a17 ("NFSD: add delegation reaper to react to low memory condition")
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  fs/nfsd/nfs4state.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index b7a0cfd05401..9ef32b19198c 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -6867,7 +6867,8 @@ deleg_reaper(struct nfsd_net *nn)
>  				clp->cl_ra_time < 5)) {
>  			continue;
>  		}
> -		list_add(&clp->cl_ra_cblist, &cblist);
> +		if (clp->cl_cb_state == NFSD4_CB_UP)
> +			list_add(&clp->cl_ra_cblist, &cblist);
>  
>  		/* release in nfsd4_cb_recall_any_release */
>  		kref_get(&clp->cl_nfsdfs.cl_ref);

Sounds like a reasonable thing to do.

Reviewed-by: Jeff Layton <jlayton@kernel.org>