Benny Halevy wrote:
> Add a cl_use_count atomic counter to struct nfs4_client.
> Hold a use count while the client is in use by a compound that begins
> with SEQUENCE.
> Renew the client when the comound completes.
> The laundromat skips clients that have a positive use count.
> Otherwise, the laundromat marks the client as expired by setting
> cl_use_count to -1.
>
> Note that we don't want to use the state lock to synchronize with nfsd4_sequence
> as we want to diminish the state lock scope.
> An alternative to using atomic_cmpxchg is to grab the sessionid_lock spin lock
> while accessing cl_use_count, but that would cause some contention in the
> laundromat if it needs to lock and unlock it for every client.
>
> Signed-off-by: Benny Halevy <bhalevy@xxxxxxxxxxx>
> ---
> fs/nfsd/nfs4state.c | 40 ++++++++++++++++++++++++++++++++++------
> fs/nfsd/nfs4xdr.c | 2 ++
> fs/nfsd/state.h | 9 +++++++++
> 3 files changed, 45 insertions(+), 6 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 50b75af..c95ddca 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -647,6 +647,14 @@ renew_client(struct nfs4_client *clp)
> clp->cl_time = get_seconds();
> }
>
> +void
> +renew_nfs4_client(struct nfs4_client *clp)
> +{
> + nfs4_lock_state();
> + renew_client(clp);
> + nfs4_unlock_state();
> +}
> +
> /* SETCLIENTID and SETCLIENTID_CONFIRM Helper functions */
> static int
> STALE_CLIENTID(clientid_t *clid)
> @@ -715,6 +723,24 @@ put_nfs4_client(struct nfs4_client *clp)
> free_client(clp);
> }
>
> +/*
> + * atomically mark client as used, as long as it's not already expired.
> + * return 0 on success, or a negative value if client already expired.
> + */
> +int
> +use_nfs4_client(struct nfs4_client *clp)
> +{
> + int orig;
> +
> + do {
> + orig = atomic_read(&clp->cl_use_count);
> + if (orig < 0)
> + return orig;
> + } while (atomic_cmpxchg(&clp->cl_use_count, orig, orig + 1) != orig);
> +
> + return 0;
> +}
> +
> static void
> expire_client(struct nfs4_client *clp)
> {
> @@ -840,6 +866,7 @@ static struct nfs4_client *create_client(struct xdr_netobj name, char *recdir,
>
> memcpy(clp->cl_recdir, recdir, HEXDIR_LEN);
> atomic_set(&clp->cl_count, 1);
> + atomic_set(&clp->cl_use_count, 0);
> atomic_set(&clp->cl_cb_conn.cb_set, 0);
> INIT_LIST_HEAD(&clp->cl_idhash);
> INIT_LIST_HEAD(&clp->cl_strhash);
> @@ -1423,6 +1450,10 @@ nfsd4_sequence(struct svc_rqst *rqstp,
> if (!session)
> goto out;
>
> + /* keep the client from expiring */
> + if (use_nfs4_client(cstate->session->se_client) < 0)
> + goto out;
> +
> status = nfserr_badslot;
> if (seq->slotid >= session->se_fchannel.maxreqs)
> goto out;
> @@ -1463,12 +1494,6 @@ out:
> get_nfs4_client(cstate->session->se_client);
> }
> spin_unlock(&sessionid_lock);
> - /* Renew the clientid on success and on replay */
> - if (cstate->session) {
> - nfs4_lock_state();
> - renew_client(session->se_client);
> - nfs4_unlock_state();
> - }
> dprintk("%s: return %d\n", __func__, ntohl(status));
> return status;
> }
> @@ -2575,6 +2600,9 @@ nfs4_laundromat(void)
> nfsd4_end_grace();
> list_for_each_safe(pos, next, &client_lru) {
> clp = list_entry(pos, struct nfs4_client, cl_lru);
> + /* skip client if in use (cl_use_count is greater than zero) */
> + if (atomic_cmpxchg(&clp->cl_use_count, 0, -1) > 0)
> + continue;
I'll move that check after the time comparison
since there's no need for the atomic instruction if the client's
time out hasn't expired yet.
Benny
> if (time_after((unsigned long)clp->cl_time, (unsigned long)cutoff)) {
> t = clp->cl_time - cutoff;
> if (clientid_val > t)
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index aed733c..0f0b857 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -3313,6 +3313,8 @@ nfs4svc_encode_compoundres(struct svc_rqst *rqstp, __be32 *p, struct nfsd4_compo
> dprintk("%s: SET SLOT STATE TO AVAILABLE\n", __func__);
> cs->slot->sl_inuse = false;
> }
> + renew_nfs4_client(cs->session->se_client);
> + unuse_nfs4_client(cs->session->se_client);
> put_nfs4_client(cs->session->se_client);
> nfsd4_put_session(cs->session);
> }
> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
> index e3c002e..806d9b8 100644
> --- a/fs/nfsd/state.h
> +++ b/fs/nfsd/state.h
> @@ -214,6 +214,7 @@ struct nfs4_client {
> nfs4_verifier cl_confirm; /* generated by server */
> struct nfs4_cb_conn cl_cb_conn; /* callback info */
> atomic_t cl_count; /* ref count */
> + atomic_t cl_use_count; /* session use count */
> u32 cl_firststate; /* recovery dir creation */
>
> /* for nfs41 */
> @@ -237,6 +238,12 @@ get_nfs4_client(struct nfs4_client *clp)
> atomic_inc(&clp->cl_count);
> }
>
> +static inline void
> +unuse_nfs4_client(struct nfs4_client *clp)
> +{
> + atomic_dec(&clp->cl_use_count);
> +}
> +
> /* struct nfs4_client_reset
> * one per old client. Populates reset_str_hashtbl. Filled from conf_id_hashtbl
> * upon lease reset, or from upcall to state_daemon (to read in state
> @@ -384,6 +391,8 @@ extern void nfs4_unlock_state(void);
> extern int nfs4_in_grace(void);
> extern __be32 nfs4_check_open_reclaim(clientid_t *clid);
> extern void put_nfs4_client(struct nfs4_client *clp);
> +extern int use_nfs4_client(struct nfs4_client *clp);
> +extern void renew_nfs4_client(struct nfs4_client *clp);
> extern void nfs4_free_stateowner(struct kref *kref);
> extern int set_callback_cred(void);
> extern void nfsd4_probe_callback(struct nfs4_client *clp);
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