Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

[mirror_ubuntu-zesty-kernel.git] / drivers / staging / lustre / lnet / klnds / socklnd / socklnd_lib-linux.c

/*
 * GPL HEADER START
 *
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 only,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License version 2 for more details (a copy is included
 * in the LICENSE file that accompanied this code).
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; If not, see
 * http://www.sun.com/software/products/lustre/docs/GPLv2.pdf
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 *
 * GPL HEADER END
 */
/*
 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Use is subject to license terms.
 *
 * Copyright (c) 2011, 2012, Intel Corporation.
 */
/*
 * This file is part of Lustre, http://www.lustre.org/
 * Lustre is a trademark of Sun Microsystems, Inc.
 */

#include "socklnd.h"

int
ksocknal_lib_get_conn_addrs (ksock_conn_t *conn)
{
        int rc = libcfs_sock_getaddr(conn->ksnc_sock, 1,
                                     &conn->ksnc_ipaddr,
                                     &conn->ksnc_port);

        /* Didn't need the {get,put}connsock dance to deref ksnc_sock... */
        LASSERT (!conn->ksnc_closing);

        if (rc != 0) {
                CERROR ("Error %d getting sock peer IP\n", rc);
                return rc;
        }

        rc = libcfs_sock_getaddr(conn->ksnc_sock, 0,
                                 &conn->ksnc_myipaddr, NULL);
        if (rc != 0) {
                CERROR ("Error %d getting sock local IP\n", rc);
                return rc;
        }

        return 0;
}

int
ksocknal_lib_zc_capable(ksock_conn_t *conn)
{
        int  caps = conn->ksnc_sock->sk->sk_route_caps;

        if (conn->ksnc_proto == &ksocknal_protocol_v1x)
                return 0;

        /* ZC if the socket supports scatter/gather and doesn't need software
         * checksums */
        return ((caps & NETIF_F_SG) != 0 && (caps & NETIF_F_ALL_CSUM) != 0);
}

int
ksocknal_lib_send_iov (ksock_conn_t *conn, ksock_tx_t *tx)
{
        struct socket *sock = conn->ksnc_sock;
        int         nob;
        int         rc;

        if (*ksocknal_tunables.ksnd_enable_csum && /* checksum enabled */
            conn->ksnc_proto == &ksocknal_protocol_v2x && /* V2.x connection  */
            tx->tx_nob == tx->tx_resid           && /* frist sending    */
            tx->tx_msg.ksm_csum == 0)                /* not checksummed  */
                ksocknal_lib_csum_tx(tx);

        /* NB we can't trust socket ops to either consume our iovs
         * or leave them alone. */

        {
#if SOCKNAL_SINGLE_FRAG_TX
                struct iovec    scratch;
                struct iovec   *scratchiov = &scratch;
                unsigned int    niov = 1;
#else
                struct iovec   *scratchiov = conn->ksnc_scheduler->kss_scratch_iov;
                unsigned int    niov = tx->tx_niov;
#endif
                struct msghdr msg = {.msg_flags = MSG_DONTWAIT};
                int  i;

                for (nob = i = 0; i < niov; i++) {
                        scratchiov[i] = tx->tx_iov[i];
                        nob += scratchiov[i].iov_len;
                }

                if (!list_empty(&conn->ksnc_tx_queue) ||
                    nob < tx->tx_resid)
                        msg.msg_flags |= MSG_MORE;

                rc = kernel_sendmsg(sock, &msg, (struct kvec *)scratchiov, niov, nob);
        }
        return rc;
}

int
ksocknal_lib_send_kiov (ksock_conn_t *conn, ksock_tx_t *tx)
{
        struct socket *sock = conn->ksnc_sock;
        lnet_kiov_t   *kiov = tx->tx_kiov;
        int         rc;
        int         nob;

        /* Not NOOP message */
        LASSERT (tx->tx_lnetmsg != NULL);

        /* NB we can't trust socket ops to either consume our iovs
         * or leave them alone. */
        if (tx->tx_msg.ksm_zc_cookies[0] != 0) {
                /* Zero copy is enabled */
                struct sock   *sk = sock->sk;
                struct page   *page = kiov->kiov_page;
                int         offset = kiov->kiov_offset;
                int         fragsize = kiov->kiov_len;
                int         msgflg = MSG_DONTWAIT;

                CDEBUG(D_NET, "page %p + offset %x for %d\n",
                               page, offset, kiov->kiov_len);

                if (!list_empty(&conn->ksnc_tx_queue) ||
                    fragsize < tx->tx_resid)
                        msgflg |= MSG_MORE;

                if (sk->sk_prot->sendpage != NULL) {
                        rc = sk->sk_prot->sendpage(sk, page,
                                                   offset, fragsize, msgflg);
                } else {
                        rc = cfs_tcp_sendpage(sk, page, offset, fragsize,
                                              msgflg);
                }
        } else {
#if SOCKNAL_SINGLE_FRAG_TX || !SOCKNAL_RISK_KMAP_DEADLOCK
                struct iovec  scratch;
                struct iovec *scratchiov = &scratch;
                unsigned int  niov = 1;
#else
#ifdef CONFIG_HIGHMEM
#warning "XXX risk of kmap deadlock on multiple frags..."
#endif
                struct iovec *scratchiov = conn->ksnc_scheduler->kss_scratch_iov;
                unsigned int  niov = tx->tx_nkiov;
#endif
                struct msghdr msg = {.msg_flags = MSG_DONTWAIT};
                int        i;

                for (nob = i = 0; i < niov; i++) {
                        scratchiov[i].iov_base = kmap(kiov[i].kiov_page) +
                                                 kiov[i].kiov_offset;
                        nob += scratchiov[i].iov_len = kiov[i].kiov_len;
                }

                if (!list_empty(&conn->ksnc_tx_queue) ||
                    nob < tx->tx_resid)
                        msg.msg_flags |= MSG_MORE;

                rc = kernel_sendmsg(sock, &msg, (struct kvec *)scratchiov, niov, nob);

                for (i = 0; i < niov; i++)
                        kunmap(kiov[i].kiov_page);
        }
        return rc;
}

void
ksocknal_lib_eager_ack (ksock_conn_t *conn)
{
        int         opt = 1;
        mm_segment_t   oldmm = get_fs();
        struct socket *sock = conn->ksnc_sock;

        /* Remind the socket to ACK eagerly.  If I don't, the socket might
         * think I'm about to send something it could piggy-back the ACK
         * on, introducing delay in completing zero-copy sends in my
         * peer. */

        set_fs(KERNEL_DS);
        sock->ops->setsockopt (sock, SOL_TCP, TCP_QUICKACK,
                               (char *)&opt, sizeof (opt));
        set_fs(oldmm);
}

int
ksocknal_lib_recv_iov (ksock_conn_t *conn)
{
#if SOCKNAL_SINGLE_FRAG_RX
        struct iovec  scratch;
        struct iovec *scratchiov = &scratch;
        unsigned int  niov = 1;
#else
        struct iovec *scratchiov = conn->ksnc_scheduler->kss_scratch_iov;
        unsigned int  niov = conn->ksnc_rx_niov;
#endif
        struct iovec *iov = conn->ksnc_rx_iov;
        struct msghdr msg = {
                .msg_flags      = 0
        };
        int       nob;
        int       i;
        int       rc;
        int       fragnob;
        int       sum;
        __u32   saved_csum;

        /* NB we can't trust socket ops to either consume our iovs
         * or leave them alone. */
        LASSERT (niov > 0);

        for (nob = i = 0; i < niov; i++) {
                scratchiov[i] = iov[i];
                nob += scratchiov[i].iov_len;
        }
        LASSERT (nob <= conn->ksnc_rx_nob_wanted);

        rc = kernel_recvmsg(conn->ksnc_sock, &msg,
                (struct kvec *)scratchiov, niov, nob, MSG_DONTWAIT);

        saved_csum = 0;
        if (conn->ksnc_proto == &ksocknal_protocol_v2x) {
                saved_csum = conn->ksnc_msg.ksm_csum;
                conn->ksnc_msg.ksm_csum = 0;
        }

        if (saved_csum != 0) {
                /* accumulate checksum */
                for (i = 0, sum = rc; sum > 0; i++, sum -= fragnob) {
                        LASSERT (i < niov);

                        fragnob = iov[i].iov_len;
                        if (fragnob > sum)
                                fragnob = sum;

                        conn->ksnc_rx_csum = ksocknal_csum(conn->ksnc_rx_csum,
                                                           iov[i].iov_base, fragnob);
                }
                conn->ksnc_msg.ksm_csum = saved_csum;
        }

        return rc;
}

static void
ksocknal_lib_kiov_vunmap(void *addr)
{
        if (addr == NULL)
                return;

        vunmap(addr);
}

static void *
ksocknal_lib_kiov_vmap(lnet_kiov_t *kiov, int niov,
                       struct iovec *iov, struct page **pages)
{
        void         *addr;
        int            nob;
        int            i;

        if (!*ksocknal_tunables.ksnd_zc_recv || pages == NULL)
                return NULL;

        LASSERT (niov <= LNET_MAX_IOV);

        if (niov < 2 ||
            niov < *ksocknal_tunables.ksnd_zc_recv_min_nfrags)
                return NULL;

        for (nob = i = 0; i < niov; i++) {
                if ((kiov[i].kiov_offset != 0 && i > 0) ||
                    (kiov[i].kiov_offset + kiov[i].kiov_len != PAGE_CACHE_SIZE && i < niov - 1))
                        return NULL;

                pages[i] = kiov[i].kiov_page;
                nob += kiov[i].kiov_len;
        }

        addr = vmap(pages, niov, VM_MAP, PAGE_KERNEL);
        if (addr == NULL)
                return NULL;

        iov->iov_base = addr + kiov[0].kiov_offset;
        iov->iov_len = nob;

        return addr;
}

int
ksocknal_lib_recv_kiov (ksock_conn_t *conn)
{
#if SOCKNAL_SINGLE_FRAG_RX || !SOCKNAL_RISK_KMAP_DEADLOCK
        struct iovec   scratch;
        struct iovec  *scratchiov = &scratch;
        struct page  **pages      = NULL;
        unsigned int   niov       = 1;
#else
#ifdef CONFIG_HIGHMEM
#warning "XXX risk of kmap deadlock on multiple frags..."
#endif
        struct iovec  *scratchiov = conn->ksnc_scheduler->kss_scratch_iov;
        struct page  **pages      = conn->ksnc_scheduler->kss_rx_scratch_pgs;
        unsigned int   niov       = conn->ksnc_rx_nkiov;
#endif
        lnet_kiov_t   *kiov = conn->ksnc_rx_kiov;
        struct msghdr msg = {
                .msg_flags      = 0
        };
        int       nob;
        int       i;
        int       rc;
        void    *base;
        void    *addr;
        int       sum;
        int       fragnob;
        int n;

        /* NB we can't trust socket ops to either consume our iovs
         * or leave them alone. */
        addr = ksocknal_lib_kiov_vmap(kiov, niov, scratchiov, pages);
        if (addr != NULL) {
                nob = scratchiov[0].iov_len;
                n = 1;

        } else {
                for (nob = i = 0; i < niov; i++) {
                        nob += scratchiov[i].iov_len = kiov[i].kiov_len;
                        scratchiov[i].iov_base = kmap(kiov[i].kiov_page) +
                                                 kiov[i].kiov_offset;
                }
                n = niov;
        }

        LASSERT (nob <= conn->ksnc_rx_nob_wanted);

        rc = kernel_recvmsg(conn->ksnc_sock, &msg,
                        (struct kvec *)scratchiov, n, nob, MSG_DONTWAIT);

        if (conn->ksnc_msg.ksm_csum != 0) {
                for (i = 0, sum = rc; sum > 0; i++, sum -= fragnob) {
                        LASSERT (i < niov);

                        /* Dang! have to kmap again because I have nowhere to stash the
                         * mapped address.  But by doing it while the page is still
                         * mapped, the kernel just bumps the map count and returns me
                         * the address it stashed. */
                        base = kmap(kiov[i].kiov_page) + kiov[i].kiov_offset;
                        fragnob = kiov[i].kiov_len;
                        if (fragnob > sum)
                                fragnob = sum;

                        conn->ksnc_rx_csum = ksocknal_csum(conn->ksnc_rx_csum,
                                                           base, fragnob);

                        kunmap(kiov[i].kiov_page);
                }
        }

        if (addr != NULL) {
                ksocknal_lib_kiov_vunmap(addr);
        } else {
                for (i = 0; i < niov; i++)
                        kunmap(kiov[i].kiov_page);
        }

        return (rc);
}

void
ksocknal_lib_csum_tx(ksock_tx_t *tx)
{
        int       i;
        __u32   csum;
        void    *base;

        LASSERT(tx->tx_iov[0].iov_base == (void *)&tx->tx_msg);
        LASSERT(tx->tx_conn != NULL);
        LASSERT(tx->tx_conn->ksnc_proto == &ksocknal_protocol_v2x);

        tx->tx_msg.ksm_csum = 0;

        csum = ksocknal_csum(~0, (void *)tx->tx_iov[0].iov_base,
                             tx->tx_iov[0].iov_len);

        if (tx->tx_kiov != NULL) {
                for (i = 0; i < tx->tx_nkiov; i++) {
                        base = kmap(tx->tx_kiov[i].kiov_page) +
                               tx->tx_kiov[i].kiov_offset;

                        csum = ksocknal_csum(csum, base, tx->tx_kiov[i].kiov_len);

                        kunmap(tx->tx_kiov[i].kiov_page);
                }
        } else {
                for (i = 1; i < tx->tx_niov; i++)
                        csum = ksocknal_csum(csum, tx->tx_iov[i].iov_base,
                                             tx->tx_iov[i].iov_len);
        }

        if (*ksocknal_tunables.ksnd_inject_csum_error) {
                csum++;
                *ksocknal_tunables.ksnd_inject_csum_error = 0;
        }

        tx->tx_msg.ksm_csum = csum;
}

int
ksocknal_lib_get_conn_tunables (ksock_conn_t *conn, int *txmem, int *rxmem, int *nagle)
{
        mm_segment_t   oldmm = get_fs ();
        struct socket *sock = conn->ksnc_sock;
        int         len;
        int         rc;

        rc = ksocknal_connsock_addref(conn);
        if (rc != 0) {
                LASSERT (conn->ksnc_closing);
                *txmem = *rxmem = *nagle = 0;
                return (-ESHUTDOWN);
        }

        rc = libcfs_sock_getbuf(sock, txmem, rxmem);
        if (rc == 0) {
                len = sizeof(*nagle);
                set_fs(KERNEL_DS);
                rc = sock->ops->getsockopt(sock, SOL_TCP, TCP_NODELAY,
                                           (char *)nagle, &len);
                set_fs(oldmm);
        }

        ksocknal_connsock_decref(conn);

        if (rc == 0)
                *nagle = !*nagle;
        else
                *txmem = *rxmem = *nagle = 0;

        return (rc);
}

int
ksocknal_lib_setup_sock (struct socket *sock)
{
        mm_segment_t    oldmm = get_fs ();
        int          rc;
        int          option;
        int          keep_idle;
        int          keep_intvl;
        int          keep_count;
        int          do_keepalive;
        struct linger   linger;

        sock->sk->sk_allocation = GFP_NOFS;

        /* Ensure this socket aborts active sends immediately when we close
         * it. */

        linger.l_onoff = 0;
        linger.l_linger = 0;

        set_fs (KERNEL_DS);
        rc = sock_setsockopt (sock, SOL_SOCKET, SO_LINGER,
                              (char *)&linger, sizeof (linger));
        set_fs (oldmm);
        if (rc != 0) {
                CERROR ("Can't set SO_LINGER: %d\n", rc);
                return (rc);
        }

        option = -1;
        set_fs (KERNEL_DS);
        rc = sock->ops->setsockopt (sock, SOL_TCP, TCP_LINGER2,
                                    (char *)&option, sizeof (option));
        set_fs (oldmm);
        if (rc != 0) {
                CERROR ("Can't set SO_LINGER2: %d\n", rc);
                return (rc);
        }

        if (!*ksocknal_tunables.ksnd_nagle) {
                option = 1;

                set_fs (KERNEL_DS);
                rc = sock->ops->setsockopt (sock, SOL_TCP, TCP_NODELAY,
                                            (char *)&option, sizeof (option));
                set_fs (oldmm);
                if (rc != 0) {
                        CERROR ("Can't disable nagle: %d\n", rc);
                        return (rc);
                }
        }

        rc = libcfs_sock_setbuf(sock,
                                *ksocknal_tunables.ksnd_tx_buffer_size,
                                *ksocknal_tunables.ksnd_rx_buffer_size);
        if (rc != 0) {
                CERROR ("Can't set buffer tx %d, rx %d buffers: %d\n",
                        *ksocknal_tunables.ksnd_tx_buffer_size,
                        *ksocknal_tunables.ksnd_rx_buffer_size, rc);
                return (rc);
        }

/* TCP_BACKOFF_* sockopt tunables unsupported in stock kernels */

        /* snapshot tunables */
        keep_idle  = *ksocknal_tunables.ksnd_keepalive_idle;
        keep_count = *ksocknal_tunables.ksnd_keepalive_count;
        keep_intvl = *ksocknal_tunables.ksnd_keepalive_intvl;

        do_keepalive = (keep_idle > 0 && keep_count > 0 && keep_intvl > 0);

        option = (do_keepalive ? 1 : 0);
        set_fs (KERNEL_DS);
        rc = sock_setsockopt (sock, SOL_SOCKET, SO_KEEPALIVE,
                              (char *)&option, sizeof (option));
        set_fs (oldmm);
        if (rc != 0) {
                CERROR ("Can't set SO_KEEPALIVE: %d\n", rc);
                return (rc);
        }

        if (!do_keepalive)
                return (0);

        set_fs (KERNEL_DS);
        rc = sock->ops->setsockopt (sock, SOL_TCP, TCP_KEEPIDLE,
                                    (char *)&keep_idle, sizeof (keep_idle));
        set_fs (oldmm);
        if (rc != 0) {
                CERROR ("Can't set TCP_KEEPIDLE: %d\n", rc);
                return (rc);
        }

        set_fs (KERNEL_DS);
        rc = sock->ops->setsockopt (sock, SOL_TCP, TCP_KEEPINTVL,
                                    (char *)&keep_intvl, sizeof (keep_intvl));
        set_fs (oldmm);
        if (rc != 0) {
                CERROR ("Can't set TCP_KEEPINTVL: %d\n", rc);
                return (rc);
        }

        set_fs (KERNEL_DS);
        rc = sock->ops->setsockopt (sock, SOL_TCP, TCP_KEEPCNT,
                                    (char *)&keep_count, sizeof (keep_count));
        set_fs (oldmm);
        if (rc != 0) {
                CERROR ("Can't set TCP_KEEPCNT: %d\n", rc);
                return (rc);
        }

        return (0);
}

void
ksocknal_lib_push_conn (ksock_conn_t *conn)
{
        struct sock    *sk;
        struct tcp_sock *tp;
        int          nonagle;
        int          val = 1;
        int          rc;
        mm_segment_t    oldmm;

        rc = ksocknal_connsock_addref(conn);
        if (rc != 0)                        /* being shut down */
                return;

        sk = conn->ksnc_sock->sk;
        tp = tcp_sk(sk);

        lock_sock (sk);
        nonagle = tp->nonagle;
        tp->nonagle = 1;
        release_sock (sk);

        oldmm = get_fs ();
        set_fs (KERNEL_DS);

        rc = sk->sk_prot->setsockopt (sk, SOL_TCP, TCP_NODELAY,
                                      (char *)&val, sizeof (val));
        LASSERT (rc == 0);

        set_fs (oldmm);

        lock_sock (sk);
        tp->nonagle = nonagle;
        release_sock (sk);

        ksocknal_connsock_decref(conn);
}

extern void ksocknal_read_callback (ksock_conn_t *conn);
extern void ksocknal_write_callback (ksock_conn_t *conn);
/*
 * socket call back in Linux
 */
static void
ksocknal_data_ready (struct sock *sk, int n)
{
        ksock_conn_t  *conn;

        /* interleave correctly with closing sockets... */
        LASSERT(!in_irq());
        read_lock(&ksocknal_data.ksnd_global_lock);

        conn = sk->sk_user_data;
        if (conn == NULL) {          /* raced with ksocknal_terminate_conn */
                LASSERT (sk->sk_data_ready != &ksocknal_data_ready);
                sk->sk_data_ready (sk, n);
        } else
                ksocknal_read_callback(conn);

        read_unlock(&ksocknal_data.ksnd_global_lock);
}

static void
ksocknal_write_space (struct sock *sk)
{
        ksock_conn_t  *conn;
        int         wspace;
        int         min_wpace;

        /* interleave correctly with closing sockets... */
        LASSERT(!in_irq());
        read_lock(&ksocknal_data.ksnd_global_lock);

        conn = sk->sk_user_data;
        wspace = SOCKNAL_WSPACE(sk);
        min_wpace = SOCKNAL_MIN_WSPACE(sk);

        CDEBUG(D_NET, "sk %p wspace %d low water %d conn %p%s%s%s\n",
               sk, wspace, min_wpace, conn,
               (conn == NULL) ? "" : (conn->ksnc_tx_ready ?
                                      " ready" : " blocked"),
               (conn == NULL) ? "" : (conn->ksnc_tx_scheduled ?
                                      " scheduled" : " idle"),
               (conn == NULL) ? "" : (list_empty (&conn->ksnc_tx_queue) ?
                                      " empty" : " queued"));

        if (conn == NULL) {          /* raced with ksocknal_terminate_conn */
                LASSERT (sk->sk_write_space != &ksocknal_write_space);
                sk->sk_write_space (sk);

                read_unlock(&ksocknal_data.ksnd_global_lock);
                return;
        }

        if (wspace >= min_wpace) {            /* got enough space */
                ksocknal_write_callback(conn);

                /* Clear SOCK_NOSPACE _after_ ksocknal_write_callback so the
                 * ENOMEM check in ksocknal_transmit is race-free (think about
                 * it). */

                clear_bit (SOCK_NOSPACE, &sk->sk_socket->flags);
        }

        read_unlock(&ksocknal_data.ksnd_global_lock);
}

void
ksocknal_lib_save_callback(struct socket *sock, ksock_conn_t *conn)
{
        conn->ksnc_saved_data_ready = sock->sk->sk_data_ready;
        conn->ksnc_saved_write_space = sock->sk->sk_write_space;
}

void
ksocknal_lib_set_callback(struct socket *sock,  ksock_conn_t *conn)
{
        sock->sk->sk_user_data = conn;
        sock->sk->sk_data_ready = ksocknal_data_ready;
        sock->sk->sk_write_space = ksocknal_write_space;
        return;
}

void
ksocknal_lib_reset_callback(struct socket *sock, ksock_conn_t *conn)
{
        /* Remove conn's network callbacks.
         * NB I _have_ to restore the callback, rather than storing a noop,
         * since the socket could survive past this module being unloaded!! */
        sock->sk->sk_data_ready = conn->ksnc_saved_data_ready;
        sock->sk->sk_write_space = conn->ksnc_saved_write_space;

        /* A callback could be in progress already; they hold a read lock
         * on ksnd_global_lock (to serialise with me) and NOOP if
         * sk_user_data is NULL. */
        sock->sk->sk_user_data = NULL;

        return ;
}

int
ksocknal_lib_memory_pressure(ksock_conn_t *conn)
{
        int         rc = 0;
        ksock_sched_t *sched;

        sched = conn->ksnc_scheduler;
        spin_lock_bh(&sched->kss_lock);

        if (!SOCK_TEST_NOSPACE(conn->ksnc_sock) &&
            !conn->ksnc_tx_ready) {
                /* SOCK_NOSPACE is set when the socket fills
                 * and cleared in the write_space callback
                 * (which also sets ksnc_tx_ready).  If
                 * SOCK_NOSPACE and ksnc_tx_ready are BOTH
                 * zero, I didn't fill the socket and
                 * write_space won't reschedule me, so I
                 * return -ENOMEM to get my caller to retry
                 * after a timeout */
                rc = -ENOMEM;
        }

        spin_unlock_bh(&sched->kss_lock);

        return rc;
}