/* * net/core/dst.c Protocol independent destination cache. * * Authors: Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru> * */ #include <linux/bitops.h> #include <linux/errno.h> #include <linux/init.h> #include <linux/kernel.h> #include <linux/workqueue.h> #include <linux/mm.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/netdevice.h> #include <linux/skbuff.h> #include <linux/string.h> #include <linux/types.h> #include <net/net_namespace.h> #include <linux/sched.h> #include <linux/prefetch.h> #include <net/dst.h> /* * Theory of operations: * 1) We use a list, protected by a spinlock, to add * new entries from both BH and non-BH context. * 2) In order to keep spinlock held for a small delay, * we use a second list where are stored long lived * entries, that are handled by the garbage collect thread * fired by a workqueue. * 3) This list is guarded by a mutex, * so that the gc_task and dst_dev_event() can be synchronized. */ /* * We want to keep lock & list close together * to dirty as few cache lines as possible in __dst_free(). * As this is not a very strong hint, we dont force an alignment on SMP. */ static struct { spinlock_t lock; struct dst_entry *list; unsigned long timer_inc; unsigned long timer_expires; } dst_garbage = { .lock = __SPIN_LOCK_UNLOCKED(dst_garbage.lock), .timer_inc = DST_GC_MAX, }; static void dst_gc_task(struct work_struct *work); static void ___dst_free(struct dst_entry *dst); static DECLARE_DELAYED_WORK(dst_gc_work, dst_gc_task); static DEFINE_MUTEX(dst_gc_mutex); /* * long lived entries are maintained in this list, guarded by dst_gc_mutex */ static struct dst_entry *dst_busy_list; static void dst_gc_task(struct work_struct *work) { int delayed = 0; int work_performed = 0; unsigned long expires = ~0L; struct dst_entry *dst, *next, head; struct dst_entry *last = &head; mutex_lock(&dst_gc_mutex); next = dst_busy_list; loop: while ((dst = next) != NULL) { next = dst->next; prefetch(&next->next); cond_resched(); if (likely(atomic_read(&dst->__refcnt))) { last->next = dst; last = dst; delayed++; continue; } work_performed++; dst = dst_destroy(dst); if (dst) { /* NOHASH and still referenced. Unless it is already * on gc list, invalidate it and add to gc list. * * Note: this is temporary. Actually, NOHASH dst's * must be obsoleted when parent is obsoleted. * But we do not have state "obsoleted, but * referenced by parent", so it is right. */ if (dst->obsolete > 0) continue; ___dst_free(dst); dst->next = next; next = dst; } } spin_lock_bh(&dst_garbage.lock); next = dst_garbage.list; if (next) { dst_garbage.list = NULL; spin_unlock_bh(&dst_garbage.lock); goto loop; } last->next = NULL; dst_busy_list = head.next; if (!dst_busy_list) dst_garbage.timer_inc = DST_GC_MAX; else { /* * if we freed less than 1/10 of delayed entries, * we can sleep longer. */ if (work_performed <= delayed/10) { dst_garbage.timer_expires += dst_garbage.timer_inc; if (dst_garbage.timer_expires > DST_GC_MAX) dst_garbage.timer_expires = DST_GC_MAX; dst_garbage.timer_inc += DST_GC_INC; } else { dst_garbage.timer_inc = DST_GC_INC; dst_garbage.timer_expires = DST_GC_MIN; } expires = dst_garbage.timer_expires; /* * if the next desired timer is more than 4 seconds in the * future then round the timer to whole seconds */ if (expires > 4*HZ) expires = round_jiffies_relative(expires); schedule_delayed_work(&dst_gc_work, expires); } spin_unlock_bh(&dst_garbage.lock); mutex_unlock(&dst_gc_mutex); } int dst_discard(struct sk_buff *skb) { kfree_skb(skb); return 0; } EXPORT_SYMBOL(dst_discard); const u32 dst_default_metrics[RTAX_MAX + 1] = { /* This initializer is needed to force linker to place this variable * into const section. Otherwise it might end into bss section. * We really want to avoid false sharing on this variable, and catch * any writes on it. */ [RTAX_MAX] = 0xdeadbeef, }; void *dst_alloc(struct dst_ops *ops, struct net_device *dev, int initial_ref, int initial_obsolete, unsigned short flags) { struct dst_entry *dst; if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) { if (ops->gc(ops)) return NULL; } dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC); if (!dst) return NULL; dst->child = NULL; dst->dev = dev; if (dev) dev_hold(dev); dst->ops = ops; dst_init_metrics(dst, dst_default_metrics, true); dst->expires = 0UL; dst->path = dst; dst->from = NULL; #ifdef CONFIG_XFRM dst->xfrm = NULL; #endif dst->input = dst_discard; dst->output = dst_discard; dst->error = 0; dst->obsolete = initial_obsolete; dst->header_len = 0; dst->trailer_len = 0; #ifdef CONFIG_IP_ROUTE_CLASSID dst->tclassid = 0; #endif atomic_set(&dst->__refcnt, initial_ref); dst->__use = 0; dst->lastuse = jiffies; dst->flags = flags; dst->pending_confirm = 0; dst->next = NULL; if (!(flags & DST_NOCOUNT)) dst_entries_add(ops, 1); return dst; } EXPORT_SYMBOL(dst_alloc); static void ___dst_free(struct dst_entry *dst) { /* The first case (dev==NULL) is required, when protocol module is unloaded. */ if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) dst->input = dst->output = dst_discard; dst->obsolete = DST_OBSOLETE_DEAD; } void __dst_free(struct dst_entry *dst) { spin_lock_bh(&dst_garbage.lock); ___dst_free(dst); dst->next = dst_garbage.list; dst_garbage.list = dst; if (dst_garbage.timer_inc > DST_GC_INC) { dst_garbage.timer_inc = DST_GC_INC; dst_garbage.timer_expires = DST_GC_MIN; mod_delayed_work(system_wq, &dst_gc_work, dst_garbage.timer_expires); } spin_unlock_bh(&dst_garbage.lock); } EXPORT_SYMBOL(__dst_free); struct dst_entry *dst_destroy(struct dst_entry * dst) { struct dst_entry *child; smp_rmb(); again: child = dst->child; if (!(dst->flags & DST_NOCOUNT)) dst_entries_add(dst->ops, -1); if (dst->ops->destroy) dst->ops->destroy(dst); if (dst->dev) dev_put(dst->dev); kmem_cache_free(dst->ops->kmem_cachep, dst); dst = child; if (dst) { int nohash = dst->flags & DST_NOHASH; if (atomic_dec_and_test(&dst->__refcnt)) { /* We were real parent of this dst, so kill child. */ if (nohash) goto again; } else { /* Child is still referenced, return it for freeing. */ if (nohash) return dst; /* Child is still in his hash table */ } } return NULL; } EXPORT_SYMBOL(dst_destroy); void dst_release(struct dst_entry *dst) { if (dst) { int newrefcnt; newrefcnt = atomic_dec_return(&dst->__refcnt); WARN_ON(newrefcnt < 0); if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt) { dst = dst_destroy(dst); if (dst) __dst_free(dst); } } } EXPORT_SYMBOL(dst_release); u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old) { u32 *p = kmalloc(sizeof(u32) * RTAX_MAX, GFP_ATOMIC); if (p) { u32 *old_p = __DST_METRICS_PTR(old); unsigned long prev, new; memcpy(p, old_p, sizeof(u32) * RTAX_MAX); new = (unsigned long) p; prev = cmpxchg(&dst->_metrics, old, new); if (prev != old) { kfree(p); p = __DST_METRICS_PTR(prev); if (prev & DST_METRICS_READ_ONLY) p = NULL; } } return p; } EXPORT_SYMBOL(dst_cow_metrics_generic); /* Caller asserts that dst_metrics_read_only(dst) is false. */ void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old) { unsigned long prev, new; new = ((unsigned long) dst_default_metrics) | DST_METRICS_READ_ONLY; prev = cmpxchg(&dst->_metrics, old, new); if (prev == old) kfree(__DST_METRICS_PTR(old)); } EXPORT_SYMBOL(__dst_destroy_metrics_generic); /** * __skb_dst_set_noref - sets skb dst, without a reference * @skb: buffer * @dst: dst entry * @force: if force is set, use noref version even for DST_NOCACHE entries * * Sets skb dst, assuming a reference was not taken on dst * skb_dst_drop() should not dst_release() this dst */ void __skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst, bool force) { WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held()); /* If dst not in cache, we must take a reference, because * dst_release() will destroy dst as soon as its refcount becomes zero */ if (unlikely((dst->flags & DST_NOCACHE) && !force)) { dst_hold(dst); skb_dst_set(skb, dst); } else { skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF; } } EXPORT_SYMBOL(__skb_dst_set_noref); /* Dirty hack. We did it in 2.2 (in __dst_free), * we have _very_ good reasons not to repeat * this mistake in 2.3, but we have no choice * now. _It_ _is_ _explicit_ _deliberate_ * _race_ _condition_. * * Commented and originally written by Alexey. */ static void dst_ifdown(struct dst_entry *dst, struct net_device *dev, int unregister) { if (dst->ops->ifdown) dst->ops->ifdown(dst, dev, unregister); if (dev != dst->dev) return; if (!unregister) { dst->input = dst->output = dst_discard; } else { dst->dev = dev_net(dst->dev)->loopback_dev; dev_hold(dst->dev); dev_put(dev); } } static int dst_dev_event(struct notifier_block *this, unsigned long event, void *ptr) { struct net_device *dev = netdev_notifier_info_to_dev(ptr); struct dst_entry *dst, *last = NULL; switch (event) { case NETDEV_UNREGISTER_FINAL: case NETDEV_DOWN: mutex_lock(&dst_gc_mutex); for (dst = dst_busy_list; dst; dst = dst->next) { last = dst; dst_ifdown(dst, dev, event != NETDEV_DOWN); } spin_lock_bh(&dst_garbage.lock); dst = dst_garbage.list; dst_garbage.list = NULL; spin_unlock_bh(&dst_garbage.lock); if (last) last->next = dst; else dst_busy_list = dst; for (; dst; dst = dst->next) dst_ifdown(dst, dev, event != NETDEV_DOWN); mutex_unlock(&dst_gc_mutex); break; } return NOTIFY_DONE; } static struct notifier_block dst_dev_notifier = { .notifier_call = dst_dev_event, .priority = -10, /* must be called after other network notifiers */ }; void __init dst_init(void) { register_netdevice_notifier(&dst_dev_notifier); }