![Francesco Ruggeri](/assets/img/avatar_default.png)
dst_release should not access dst->flags after decrementing __refcnt to 0. The dst_entry may be in dst_busy_list and dst_gc_task may dst_destroy it before dst_release gets a chance to access dst->flags. Fixes:d69bbf88c8
("net: fix a race in dst_release()") Fixes:27b75c95f1
("net: avoid RCU for NOCACHE dst") Signed-off-by: Francesco Ruggeri <fruggeri@arista.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
483 lines
11 KiB
C
483 lines
11 KiB
C
/*
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* net/core/dst.c Protocol independent destination cache.
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*
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* Authors: Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
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*
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*/
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#include <linux/bitops.h>
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#include <linux/errno.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/workqueue.h>
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#include <linux/mm.h>
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/netdevice.h>
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#include <linux/skbuff.h>
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#include <linux/string.h>
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#include <linux/types.h>
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#include <net/net_namespace.h>
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#include <linux/sched.h>
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#include <linux/prefetch.h>
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#include <net/lwtunnel.h>
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#include <net/dst.h>
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#include <net/dst_metadata.h>
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/*
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* Theory of operations:
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* 1) We use a list, protected by a spinlock, to add
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* new entries from both BH and non-BH context.
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* 2) In order to keep spinlock held for a small delay,
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* we use a second list where are stored long lived
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* entries, that are handled by the garbage collect thread
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* fired by a workqueue.
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* 3) This list is guarded by a mutex,
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* so that the gc_task and dst_dev_event() can be synchronized.
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*/
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/*
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* We want to keep lock & list close together
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* to dirty as few cache lines as possible in __dst_free().
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* As this is not a very strong hint, we dont force an alignment on SMP.
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*/
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static struct {
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spinlock_t lock;
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struct dst_entry *list;
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unsigned long timer_inc;
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unsigned long timer_expires;
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} dst_garbage = {
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.lock = __SPIN_LOCK_UNLOCKED(dst_garbage.lock),
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.timer_inc = DST_GC_MAX,
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};
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static void dst_gc_task(struct work_struct *work);
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static void ___dst_free(struct dst_entry *dst);
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static DECLARE_DELAYED_WORK(dst_gc_work, dst_gc_task);
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static DEFINE_MUTEX(dst_gc_mutex);
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/*
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* long lived entries are maintained in this list, guarded by dst_gc_mutex
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*/
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static struct dst_entry *dst_busy_list;
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static void dst_gc_task(struct work_struct *work)
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{
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int delayed = 0;
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int work_performed = 0;
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unsigned long expires = ~0L;
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struct dst_entry *dst, *next, head;
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struct dst_entry *last = &head;
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mutex_lock(&dst_gc_mutex);
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next = dst_busy_list;
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loop:
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while ((dst = next) != NULL) {
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next = dst->next;
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prefetch(&next->next);
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cond_resched();
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if (likely(atomic_read(&dst->__refcnt))) {
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last->next = dst;
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last = dst;
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delayed++;
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continue;
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}
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work_performed++;
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dst = dst_destroy(dst);
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if (dst) {
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/* NOHASH and still referenced. Unless it is already
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* on gc list, invalidate it and add to gc list.
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*
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* Note: this is temporary. Actually, NOHASH dst's
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* must be obsoleted when parent is obsoleted.
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* But we do not have state "obsoleted, but
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* referenced by parent", so it is right.
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*/
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if (dst->obsolete > 0)
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continue;
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___dst_free(dst);
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dst->next = next;
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next = dst;
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}
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}
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spin_lock_bh(&dst_garbage.lock);
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next = dst_garbage.list;
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if (next) {
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dst_garbage.list = NULL;
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spin_unlock_bh(&dst_garbage.lock);
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goto loop;
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}
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last->next = NULL;
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dst_busy_list = head.next;
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if (!dst_busy_list)
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dst_garbage.timer_inc = DST_GC_MAX;
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else {
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/*
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* if we freed less than 1/10 of delayed entries,
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* we can sleep longer.
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*/
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if (work_performed <= delayed/10) {
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dst_garbage.timer_expires += dst_garbage.timer_inc;
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if (dst_garbage.timer_expires > DST_GC_MAX)
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dst_garbage.timer_expires = DST_GC_MAX;
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dst_garbage.timer_inc += DST_GC_INC;
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} else {
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dst_garbage.timer_inc = DST_GC_INC;
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dst_garbage.timer_expires = DST_GC_MIN;
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}
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expires = dst_garbage.timer_expires;
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/*
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* if the next desired timer is more than 4 seconds in the
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* future then round the timer to whole seconds
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*/
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if (expires > 4*HZ)
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expires = round_jiffies_relative(expires);
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schedule_delayed_work(&dst_gc_work, expires);
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}
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spin_unlock_bh(&dst_garbage.lock);
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mutex_unlock(&dst_gc_mutex);
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}
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int dst_discard_out(struct net *net, struct sock *sk, struct sk_buff *skb)
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{
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kfree_skb(skb);
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return 0;
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}
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EXPORT_SYMBOL(dst_discard_out);
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const u32 dst_default_metrics[RTAX_MAX + 1] = {
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/* This initializer is needed to force linker to place this variable
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* into const section. Otherwise it might end into bss section.
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* We really want to avoid false sharing on this variable, and catch
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* any writes on it.
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*/
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[RTAX_MAX] = 0xdeadbeef,
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};
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void dst_init(struct dst_entry *dst, struct dst_ops *ops,
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struct net_device *dev, int initial_ref, int initial_obsolete,
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unsigned short flags)
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{
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dst->child = NULL;
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dst->dev = dev;
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if (dev)
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dev_hold(dev);
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dst->ops = ops;
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dst_init_metrics(dst, dst_default_metrics, true);
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dst->expires = 0UL;
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dst->path = dst;
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dst->from = NULL;
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#ifdef CONFIG_XFRM
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dst->xfrm = NULL;
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#endif
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dst->input = dst_discard;
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dst->output = dst_discard_out;
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dst->error = 0;
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dst->obsolete = initial_obsolete;
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dst->header_len = 0;
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dst->trailer_len = 0;
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#ifdef CONFIG_IP_ROUTE_CLASSID
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dst->tclassid = 0;
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#endif
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dst->lwtstate = NULL;
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atomic_set(&dst->__refcnt, initial_ref);
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dst->__use = 0;
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dst->lastuse = jiffies;
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dst->flags = flags;
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dst->pending_confirm = 0;
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dst->next = NULL;
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if (!(flags & DST_NOCOUNT))
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dst_entries_add(ops, 1);
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}
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EXPORT_SYMBOL(dst_init);
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void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
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int initial_ref, int initial_obsolete, unsigned short flags)
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{
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struct dst_entry *dst;
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if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) {
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if (ops->gc(ops))
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return NULL;
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}
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dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
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if (!dst)
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return NULL;
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dst_init(dst, ops, dev, initial_ref, initial_obsolete, flags);
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return dst;
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}
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EXPORT_SYMBOL(dst_alloc);
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static void ___dst_free(struct dst_entry *dst)
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{
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/* The first case (dev==NULL) is required, when
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protocol module is unloaded.
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*/
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if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
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dst->input = dst_discard;
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dst->output = dst_discard_out;
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}
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dst->obsolete = DST_OBSOLETE_DEAD;
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}
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void __dst_free(struct dst_entry *dst)
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{
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spin_lock_bh(&dst_garbage.lock);
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___dst_free(dst);
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dst->next = dst_garbage.list;
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dst_garbage.list = dst;
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if (dst_garbage.timer_inc > DST_GC_INC) {
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dst_garbage.timer_inc = DST_GC_INC;
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dst_garbage.timer_expires = DST_GC_MIN;
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mod_delayed_work(system_wq, &dst_gc_work,
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dst_garbage.timer_expires);
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}
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spin_unlock_bh(&dst_garbage.lock);
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}
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EXPORT_SYMBOL(__dst_free);
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struct dst_entry *dst_destroy(struct dst_entry * dst)
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{
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struct dst_entry *child;
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smp_rmb();
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again:
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child = dst->child;
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if (!(dst->flags & DST_NOCOUNT))
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dst_entries_add(dst->ops, -1);
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if (dst->ops->destroy)
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dst->ops->destroy(dst);
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if (dst->dev)
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dev_put(dst->dev);
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lwtstate_put(dst->lwtstate);
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if (dst->flags & DST_METADATA)
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kfree(dst);
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else
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kmem_cache_free(dst->ops->kmem_cachep, dst);
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dst = child;
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if (dst) {
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int nohash = dst->flags & DST_NOHASH;
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if (atomic_dec_and_test(&dst->__refcnt)) {
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/* We were real parent of this dst, so kill child. */
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if (nohash)
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goto again;
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} else {
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/* Child is still referenced, return it for freeing. */
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if (nohash)
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return dst;
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/* Child is still in his hash table */
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}
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}
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return NULL;
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}
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EXPORT_SYMBOL(dst_destroy);
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static void dst_destroy_rcu(struct rcu_head *head)
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{
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struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
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dst = dst_destroy(dst);
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if (dst)
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__dst_free(dst);
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}
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void dst_release(struct dst_entry *dst)
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{
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if (dst) {
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int newrefcnt;
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unsigned short nocache = dst->flags & DST_NOCACHE;
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newrefcnt = atomic_dec_return(&dst->__refcnt);
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if (unlikely(newrefcnt < 0))
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net_warn_ratelimited("%s: dst:%p refcnt:%d\n",
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__func__, dst, newrefcnt);
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if (!newrefcnt && unlikely(nocache))
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call_rcu(&dst->rcu_head, dst_destroy_rcu);
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}
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}
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EXPORT_SYMBOL(dst_release);
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u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old)
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{
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u32 *p = kmalloc(sizeof(u32) * RTAX_MAX, GFP_ATOMIC);
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if (p) {
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u32 *old_p = __DST_METRICS_PTR(old);
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unsigned long prev, new;
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memcpy(p, old_p, sizeof(u32) * RTAX_MAX);
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new = (unsigned long) p;
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prev = cmpxchg(&dst->_metrics, old, new);
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if (prev != old) {
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kfree(p);
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p = __DST_METRICS_PTR(prev);
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if (prev & DST_METRICS_READ_ONLY)
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p = NULL;
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}
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}
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return p;
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}
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EXPORT_SYMBOL(dst_cow_metrics_generic);
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/* Caller asserts that dst_metrics_read_only(dst) is false. */
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void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old)
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{
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unsigned long prev, new;
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new = ((unsigned long) dst_default_metrics) | DST_METRICS_READ_ONLY;
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prev = cmpxchg(&dst->_metrics, old, new);
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if (prev == old)
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kfree(__DST_METRICS_PTR(old));
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}
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EXPORT_SYMBOL(__dst_destroy_metrics_generic);
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static struct dst_ops md_dst_ops = {
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.family = AF_UNSPEC,
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};
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static int dst_md_discard_out(struct net *net, struct sock *sk, struct sk_buff *skb)
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{
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WARN_ONCE(1, "Attempting to call output on metadata dst\n");
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kfree_skb(skb);
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return 0;
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}
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static int dst_md_discard(struct sk_buff *skb)
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{
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WARN_ONCE(1, "Attempting to call input on metadata dst\n");
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kfree_skb(skb);
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return 0;
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}
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static void __metadata_dst_init(struct metadata_dst *md_dst, u8 optslen)
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{
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struct dst_entry *dst;
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dst = &md_dst->dst;
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dst_init(dst, &md_dst_ops, NULL, 1, DST_OBSOLETE_NONE,
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DST_METADATA | DST_NOCACHE | DST_NOCOUNT);
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dst->input = dst_md_discard;
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dst->output = dst_md_discard_out;
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memset(dst + 1, 0, sizeof(*md_dst) + optslen - sizeof(*dst));
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}
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struct metadata_dst *metadata_dst_alloc(u8 optslen, gfp_t flags)
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{
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struct metadata_dst *md_dst;
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md_dst = kmalloc(sizeof(*md_dst) + optslen, flags);
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if (!md_dst)
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return NULL;
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__metadata_dst_init(md_dst, optslen);
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return md_dst;
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}
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EXPORT_SYMBOL_GPL(metadata_dst_alloc);
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struct metadata_dst __percpu *metadata_dst_alloc_percpu(u8 optslen, gfp_t flags)
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{
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int cpu;
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struct metadata_dst __percpu *md_dst;
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md_dst = __alloc_percpu_gfp(sizeof(struct metadata_dst) + optslen,
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__alignof__(struct metadata_dst), flags);
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if (!md_dst)
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return NULL;
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for_each_possible_cpu(cpu)
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__metadata_dst_init(per_cpu_ptr(md_dst, cpu), optslen);
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return md_dst;
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}
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EXPORT_SYMBOL_GPL(metadata_dst_alloc_percpu);
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/* Dirty hack. We did it in 2.2 (in __dst_free),
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* we have _very_ good reasons not to repeat
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* this mistake in 2.3, but we have no choice
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* now. _It_ _is_ _explicit_ _deliberate_
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* _race_ _condition_.
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*
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* Commented and originally written by Alexey.
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*/
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static void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
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int unregister)
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{
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if (dst->ops->ifdown)
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dst->ops->ifdown(dst, dev, unregister);
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if (dev != dst->dev)
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return;
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if (!unregister) {
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dst->input = dst_discard;
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dst->output = dst_discard_out;
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} else {
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dst->dev = dev_net(dst->dev)->loopback_dev;
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dev_hold(dst->dev);
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dev_put(dev);
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}
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}
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static int dst_dev_event(struct notifier_block *this, unsigned long event,
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void *ptr)
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{
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struct net_device *dev = netdev_notifier_info_to_dev(ptr);
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struct dst_entry *dst, *last = NULL;
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switch (event) {
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case NETDEV_UNREGISTER_FINAL:
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case NETDEV_DOWN:
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mutex_lock(&dst_gc_mutex);
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for (dst = dst_busy_list; dst; dst = dst->next) {
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last = dst;
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dst_ifdown(dst, dev, event != NETDEV_DOWN);
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}
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spin_lock_bh(&dst_garbage.lock);
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dst = dst_garbage.list;
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dst_garbage.list = NULL;
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spin_unlock_bh(&dst_garbage.lock);
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if (last)
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last->next = dst;
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else
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dst_busy_list = dst;
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for (; dst; dst = dst->next)
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dst_ifdown(dst, dev, event != NETDEV_DOWN);
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mutex_unlock(&dst_gc_mutex);
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break;
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}
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return NOTIFY_DONE;
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}
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static struct notifier_block dst_dev_notifier = {
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.notifier_call = dst_dev_event,
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.priority = -10, /* must be called after other network notifiers */
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};
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void __init dst_subsys_init(void)
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{
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register_netdevice_notifier(&dst_dev_notifier);
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}
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