inet_timewait_sock.c

Go to the documentation of this file.

/*
 * INET     An implementation of the TCP/IP protocol suite for the LINUX
 *      operating system.  INET is implemented using the  BSD Socket
 *      interface as the means of communication with the user level.
 *
 *      Generic TIME_WAIT sockets functions
 *
 *      From code orinally in TCP
 */

#include <linux/kernel.h>
#include <linux/kmemcheck.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <net/inet_hashtables.h>
#include <net/inet_timewait_sock.h>
#include <net/ip.h>


int inet_twsk_unhash(struct inet_timewait_sock *tw)
{
    if (hlist_nulls_unhashed(&tw->tw_node))
        return 0;

    hlist_nulls_del_rcu(&tw->tw_node);
    sk_nulls_node_init(&tw->tw_node);
    /*
     * We cannot call inet_twsk_put() ourself under lock,
     * caller must call it for us.
     */
    return 1;
}

int inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
              struct inet_hashinfo *hashinfo)
{
    struct inet_bind_bucket *tb = tw->tw_tb;

    if (!tb)
        return 0;

    __hlist_del(&tw->tw_bind_node);
    tw->tw_tb = NULL;
    inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
    /*
     * We cannot call inet_twsk_put() ourself under lock,
     * caller must call it for us.
     */
    return 1;
}

/* Must be called with locally disabled BHs. */
static void __inet_twsk_kill(struct inet_timewait_sock *tw,
                 struct inet_hashinfo *hashinfo)
{
    struct inet_bind_hashbucket *bhead;
    int refcnt;
    /* Unlink from established hashes. */
    spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);

    spin_lock(lock);
    refcnt = inet_twsk_unhash(tw);
    spin_unlock(lock);

    /* Disassociate with bind bucket. */
    bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), tw->tw_num,
            hashinfo->bhash_size)];

    spin_lock(&bhead->lock);
    refcnt += inet_twsk_bind_unhash(tw, hashinfo);
    spin_unlock(&bhead->lock);

#ifdef SOCK_REFCNT_DEBUG
    if (atomic_read(&tw->tw_refcnt) != 1) {
        pr_debug("%s timewait_sock %p refcnt=%d\n",
             tw->tw_prot->name, tw, atomic_read(&tw->tw_refcnt));
    }
#endif
    while (refcnt) {
        inet_twsk_put(tw);
        refcnt--;
    }
}

static noinline void inet_twsk_free(struct inet_timewait_sock *tw)
{
    struct module *owner = tw->tw_prot->owner;
    twsk_destructor((struct sock *)tw);
#ifdef SOCK_REFCNT_DEBUG
    pr_debug("%s timewait_sock %p released\n", tw->tw_prot->name, tw);
#endif
    release_net(twsk_net(tw));
    kmem_cache_free(tw->tw_prot->twsk_prot->twsk_slab, tw);
    module_put(owner);
}

void inet_twsk_put(struct inet_timewait_sock *tw)
{
    if (atomic_dec_and_test(&tw->tw_refcnt))
        inet_twsk_free(tw);
}
EXPORT_SYMBOL_GPL(inet_twsk_put);

/*
 * Enter the time wait state. This is called with locally disabled BH.
 * Essentially we whip up a timewait bucket, copy the relevant info into it
 * from the SK, and mess with hash chains and list linkage.
 */
void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
               struct inet_hashinfo *hashinfo)
{
    const struct inet_sock *inet = inet_sk(sk);
    const struct inet_connection_sock *icsk = inet_csk(sk);
    struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);
    spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
    struct inet_bind_hashbucket *bhead;
    /* Step 1: Put TW into bind hash. Original socket stays there too.
       Note, that any socket with inet->num != 0 MUST be bound in
       binding cache, even if it is closed.
     */
    bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), inet->inet_num,
            hashinfo->bhash_size)];
    spin_lock(&bhead->lock);
    tw->tw_tb = icsk->icsk_bind_hash;
    WARN_ON(!icsk->icsk_bind_hash);
    inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);
    spin_unlock(&bhead->lock);

    spin_lock(lock);

    /*
     * Step 2: Hash TW into TIMEWAIT chain.
     * Should be done before removing sk from established chain
     * because readers are lockless and search established first.
     */
    inet_twsk_add_node_rcu(tw, &ehead->twchain);

    /* Step 3: Remove SK from established hash. */
    if (__sk_nulls_del_node_init_rcu(sk))
        sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);

    /*
     * Notes :
     * - We initially set tw_refcnt to 0 in inet_twsk_alloc()
     * - We add one reference for the bhash link
     * - We add one reference for the ehash link
     * - We want this refcnt update done before allowing other
     *   threads to find this tw in ehash chain.
     */
    atomic_add(1 + 1 + 1, &tw->tw_refcnt);

    spin_unlock(lock);
}
EXPORT_SYMBOL_GPL(__inet_twsk_hashdance);

struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk, const int state)
{
    struct inet_timewait_sock *tw =
        kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,
                 GFP_ATOMIC);
    if (tw != NULL) {
        const struct inet_sock *inet = inet_sk(sk);

        kmemcheck_annotate_bitfield(tw, flags);

        /* Give us an identity. */
        tw->tw_daddr        = inet->inet_daddr;
        tw->tw_rcv_saddr    = inet->inet_rcv_saddr;
        tw->tw_bound_dev_if = sk->sk_bound_dev_if;
        tw->tw_tos      = inet->tos;
        tw->tw_num      = inet->inet_num;
        tw->tw_state        = TCP_TIME_WAIT;
        tw->tw_substate     = state;
        tw->tw_sport        = inet->inet_sport;
        tw->tw_dport        = inet->inet_dport;
        tw->tw_family       = sk->sk_family;
        tw->tw_reuse        = sk->sk_reuse;
        tw->tw_hash     = sk->sk_hash;
        tw->tw_ipv6only     = 0;
        tw->tw_transparent  = inet->transparent;
        tw->tw_prot     = sk->sk_prot_creator;
        twsk_net_set(tw, hold_net(sock_net(sk)));
        /*
         * Because we use RCU lookups, we should not set tw_refcnt
         * to a non null value before everything is setup for this
         * timewait socket.
         */
        atomic_set(&tw->tw_refcnt, 0);
        inet_twsk_dead_node_init(tw);
        __module_get(tw->tw_prot->owner);
    }

    return tw;
}
EXPORT_SYMBOL_GPL(inet_twsk_alloc);

/* Returns non-zero if quota exceeded.  */
static int inet_twdr_do_twkill_work(struct inet_timewait_death_row *twdr,
                    const int slot)
{
    struct inet_timewait_sock *tw;
    struct hlist_node *node;
    unsigned int killed;
    int ret;

    /* NOTE: compare this to previous version where lock
     * was released after detaching chain. It was racy,
     * because tw buckets are scheduled in not serialized context
     * in 2.3 (with netfilter), and with softnet it is common, because
     * soft irqs are not sequenced.
     */
    killed = 0;
    ret = 0;
rescan:
    inet_twsk_for_each_inmate(tw, node, &twdr->cells[slot]) {
        __inet_twsk_del_dead_node(tw);
        spin_unlock(&twdr->death_lock);
        __inet_twsk_kill(tw, twdr->hashinfo);
#ifdef CONFIG_NET_NS
        NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_TIMEWAITED);
#endif
        inet_twsk_put(tw);
        killed++;
        spin_lock(&twdr->death_lock);
        if (killed > INET_TWDR_TWKILL_QUOTA) {
            ret = 1;
            break;
        }

        /* While we dropped twdr->death_lock, another cpu may have
         * killed off the next TW bucket in the list, therefore
         * do a fresh re-read of the hlist head node with the
         * lock reacquired.  We still use the hlist traversal
         * macro in order to get the prefetches.
         */
        goto rescan;
    }

    twdr->tw_count -= killed;
#ifndef CONFIG_NET_NS
    NET_ADD_STATS_BH(&init_net, LINUX_MIB_TIMEWAITED, killed);
#endif
    return ret;
}

void inet_twdr_hangman(unsigned long data)
{
    struct inet_timewait_death_row *twdr;
    unsigned int need_timer;

    twdr = (struct inet_timewait_death_row *)data;
    spin_lock(&twdr->death_lock);

    if (twdr->tw_count == 0)
        goto out;

    need_timer = 0;
    if (inet_twdr_do_twkill_work(twdr, twdr->slot)) {
        twdr->thread_slots |= (1 << twdr->slot);
        schedule_work(&twdr->twkill_work);
        need_timer = 1;
    } else {
        /* We purged the entire slot, anything left?  */
        if (twdr->tw_count)
            need_timer = 1;
        twdr->slot = ((twdr->slot + 1) & (INET_TWDR_TWKILL_SLOTS - 1));
    }
    if (need_timer)
        mod_timer(&twdr->tw_timer, jiffies + twdr->period);
out:
    spin_unlock(&twdr->death_lock);
}
EXPORT_SYMBOL_GPL(inet_twdr_hangman);

void inet_twdr_twkill_work(struct work_struct *work)
{
    struct inet_timewait_death_row *twdr =
        container_of(work, struct inet_timewait_death_row, twkill_work);
    int i;

    BUILD_BUG_ON((INET_TWDR_TWKILL_SLOTS - 1) >
            (sizeof(twdr->thread_slots) * 8));

    while (twdr->thread_slots) {
        spin_lock_bh(&twdr->death_lock);
        for (i = 0; i < INET_TWDR_TWKILL_SLOTS; i++) {
            if (!(twdr->thread_slots & (1 << i)))
                continue;

            while (inet_twdr_do_twkill_work(twdr, i) != 0) {
                if (need_resched()) {
                    spin_unlock_bh(&twdr->death_lock);
                    schedule();
                    spin_lock_bh(&twdr->death_lock);
                }
            }

            twdr->thread_slots &= ~(1 << i);
        }
        spin_unlock_bh(&twdr->death_lock);
    }
}
EXPORT_SYMBOL_GPL(inet_twdr_twkill_work);

/* These are always called from BH context.  See callers in
 * tcp_input.c to verify this.
 */

/* This is for handling early-kills of TIME_WAIT sockets. */
void inet_twsk_deschedule(struct inet_timewait_sock *tw,
              struct inet_timewait_death_row *twdr)
{
    spin_lock(&twdr->death_lock);
    if (inet_twsk_del_dead_node(tw)) {
        inet_twsk_put(tw);
        if (--twdr->tw_count == 0)
            del_timer(&twdr->tw_timer);
    }
    spin_unlock(&twdr->death_lock);
    __inet_twsk_kill(tw, twdr->hashinfo);
}
EXPORT_SYMBOL(inet_twsk_deschedule);

void inet_twsk_schedule(struct inet_timewait_sock *tw,
               struct inet_timewait_death_row *twdr,
               const int timeo, const int timewait_len)
{
    struct hlist_head *list;
    int slot;

    /* timeout := RTO * 3.5
     *
     * 3.5 = 1+2+0.5 to wait for two retransmits.
     *
     * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
     * our ACK acking that FIN can be lost. If N subsequent retransmitted
     * FINs (or previous seqments) are lost (probability of such event
     * is p^(N+1), where p is probability to lose single packet and
     * time to detect the loss is about RTO*(2^N - 1) with exponential
     * backoff). Normal timewait length is calculated so, that we
     * waited at least for one retransmitted FIN (maximal RTO is 120sec).
     * [ BTW Linux. following BSD, violates this requirement waiting
     *   only for 60sec, we should wait at least for 240 secs.
     *   Well, 240 consumes too much of resources 8)
     * ]
     * This interval is not reduced to catch old duplicate and
     * responces to our wandering segments living for two MSLs.
     * However, if we use PAWS to detect
     * old duplicates, we can reduce the interval to bounds required
     * by RTO, rather than MSL. So, if peer understands PAWS, we
     * kill tw bucket after 3.5*RTO (it is important that this number
     * is greater than TS tick!) and detect old duplicates with help
     * of PAWS.
     */
    slot = (timeo + (1 << INET_TWDR_RECYCLE_TICK) - 1) >> INET_TWDR_RECYCLE_TICK;

    spin_lock(&twdr->death_lock);

    /* Unlink it, if it was scheduled */
    if (inet_twsk_del_dead_node(tw))
        twdr->tw_count--;
    else
        atomic_inc(&tw->tw_refcnt);

    if (slot >= INET_TWDR_RECYCLE_SLOTS) {
        /* Schedule to slow timer */
        if (timeo >= timewait_len) {
            slot = INET_TWDR_TWKILL_SLOTS - 1;
        } else {
            slot = DIV_ROUND_UP(timeo, twdr->period);
            if (slot >= INET_TWDR_TWKILL_SLOTS)
                slot = INET_TWDR_TWKILL_SLOTS - 1;
        }
        tw->tw_ttd = jiffies + timeo;
        slot = (twdr->slot + slot) & (INET_TWDR_TWKILL_SLOTS - 1);
        list = &twdr->cells[slot];
    } else {
        tw->tw_ttd = jiffies + (slot << INET_TWDR_RECYCLE_TICK);

        if (twdr->twcal_hand < 0) {
            twdr->twcal_hand = 0;
            twdr->twcal_jiffie = jiffies;
            twdr->twcal_timer.expires = twdr->twcal_jiffie +
                          (slot << INET_TWDR_RECYCLE_TICK);
            add_timer(&twdr->twcal_timer);
        } else {
            if (time_after(twdr->twcal_timer.expires,
                       jiffies + (slot << INET_TWDR_RECYCLE_TICK)))
                mod_timer(&twdr->twcal_timer,
                      jiffies + (slot << INET_TWDR_RECYCLE_TICK));
            slot = (twdr->twcal_hand + slot) & (INET_TWDR_RECYCLE_SLOTS - 1);
        }
        list = &twdr->twcal_row[slot];
    }

    hlist_add_head(&tw->tw_death_node, list);

    if (twdr->tw_count++ == 0)
        mod_timer(&twdr->tw_timer, jiffies + twdr->period);
    spin_unlock(&twdr->death_lock);
}
EXPORT_SYMBOL_GPL(inet_twsk_schedule);

void inet_twdr_twcal_tick(unsigned long data)
{
    struct inet_timewait_death_row *twdr;
    int n, slot;
    unsigned long j;
    unsigned long now = jiffies;
    int killed = 0;
    int adv = 0;

    twdr = (struct inet_timewait_death_row *)data;

    spin_lock(&twdr->death_lock);
    if (twdr->twcal_hand < 0)
        goto out;

    slot = twdr->twcal_hand;
    j = twdr->twcal_jiffie;

    for (n = 0; n < INET_TWDR_RECYCLE_SLOTS; n++) {
        if (time_before_eq(j, now)) {
            struct hlist_node *node, *safe;
            struct inet_timewait_sock *tw;

            inet_twsk_for_each_inmate_safe(tw, node, safe,
                               &twdr->twcal_row[slot]) {
                __inet_twsk_del_dead_node(tw);
                __inet_twsk_kill(tw, twdr->hashinfo);
#ifdef CONFIG_NET_NS
                NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_TIMEWAITKILLED);
#endif
                inet_twsk_put(tw);
                killed++;
            }
        } else {
            if (!adv) {
                adv = 1;
                twdr->twcal_jiffie = j;
                twdr->twcal_hand = slot;
            }

            if (!hlist_empty(&twdr->twcal_row[slot])) {
                mod_timer(&twdr->twcal_timer, j);
                goto out;
            }
        }
        j += 1 << INET_TWDR_RECYCLE_TICK;
        slot = (slot + 1) & (INET_TWDR_RECYCLE_SLOTS - 1);
    }
    twdr->twcal_hand = -1;

out:
    if ((twdr->tw_count -= killed) == 0)
        del_timer(&twdr->tw_timer);
#ifndef CONFIG_NET_NS
    NET_ADD_STATS_BH(&init_net, LINUX_MIB_TIMEWAITKILLED, killed);
#endif
    spin_unlock(&twdr->death_lock);
}
EXPORT_SYMBOL_GPL(inet_twdr_twcal_tick);

void inet_twsk_purge(struct inet_hashinfo *hashinfo,
             struct inet_timewait_death_row *twdr, int family)
{
    struct inet_timewait_sock *tw;
    struct sock *sk;
    struct hlist_nulls_node *node;
    unsigned int slot;

    for (slot = 0; slot <= hashinfo->ehash_mask; slot++) {
        struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
restart_rcu:
        rcu_read_lock();
restart:
        sk_nulls_for_each_rcu(sk, node, &head->twchain) {
            tw = inet_twsk(sk);
            if ((tw->tw_family != family) ||
                atomic_read(&twsk_net(tw)->count))
                continue;

            if (unlikely(!atomic_inc_not_zero(&tw->tw_refcnt)))
                continue;

            if (unlikely((tw->tw_family != family) ||
                     atomic_read(&twsk_net(tw)->count))) {
                inet_twsk_put(tw);
                goto restart;
            }

            rcu_read_unlock();
            local_bh_disable();
            inet_twsk_deschedule(tw, twdr);
            local_bh_enable();
            inet_twsk_put(tw);
            goto restart_rcu;
        }
        /* If the nulls value we got at the end of this lookup is
         * not the expected one, we must restart lookup.
         * We probably met an item that was moved to another chain.
         */
        if (get_nulls_value(node) != slot)
            goto restart;
        rcu_read_unlock();
    }
}
EXPORT_SYMBOL_GPL(inet_twsk_purge);