![Wei Wang](/assets/img/avatar_default.png)
With all the preparation work before, we are now ready to replace rwlock with rcu and spinlock in fib6_table. That means now all fib6_node in fib6_table are protected by rcu. And when freeing fib6_node, call_rcu() is used to wait for the rcu grace period before releasing the memory. When accessing fib6_node, corresponding rcu APIs need to be used. And all previous sessions protected by the write lock will now be protected by the spin lock per table. All previous sessions protected by read lock will now be protected by rcu_read_lock(). A couple of things to note here: 1. As part of the work of replacing rwlock with rcu, the linked list of fn->leaf now has to be rcu protected as well. So both fn->leaf and rt->dst.rt6_next are now __rcu tagged and corresponding rcu APIs are used when manipulating them. 2. For fn->rr_ptr, first of all, it also needs to be rcu protected now and is tagged with __rcu and rcu APIs are used in corresponding places. Secondly, fn->rr_ptr is changed in rt6_select() which is a reader thread. This makes the issue a bit complicated. We think a valid solution for it is to let rt6_select() grab the tb6_lock if it decides to change it. As it is not in the normal operation and only happens when there is no valid neighbor cache for the route, we think the performance impact should be low. 3. fib6_walk_continue() has to be called with tb6_lock held even in the route dumping related functions, e.g. inet6_dump_fib(), fib6_tables_dump() and ipv6_route_seq_ops. It is because fib6_walk_continue() makes modifications to the walker structure, and so are fib6_repair_tree() and fib6_del_route(). In order to do proper syncing between them, we need to let fib6_walk_continue() hold the lock. We may be able to do further improvement on the way we do the tree walk to get rid of the need for holding the spin lock. But not for now. 4. When fib6_del_route() removes a route from the tree, we no longer mark rt->dst.rt6_next to NULL to make simultaneous reader be able to further traverse the list with rcu. However, rt->dst.rt6_next is only valid within this same rcu period. No one should access it later. 5. All the operation of atomic_inc(rt->rt6i_ref) is changed to be performed before we publish this route (either by linking it to fn->leaf or insert it in the list pointed by fn->leaf) just to be safe because as soon as we publish the route, some read thread will be able to access it. Signed-off-by: Wei Wang <weiwan@google.com> Signed-off-by: Martin KaFai Lau <kafai@fb.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
523 lines
13 KiB
C
523 lines
13 KiB
C
/*
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* net/dst.h Protocol independent destination cache definitions.
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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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#ifndef _NET_DST_H
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#define _NET_DST_H
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#include <net/dst_ops.h>
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#include <linux/netdevice.h>
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#include <linux/rtnetlink.h>
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#include <linux/rcupdate.h>
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#include <linux/bug.h>
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#include <linux/jiffies.h>
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#include <linux/refcount.h>
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#include <net/neighbour.h>
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#include <asm/processor.h>
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#define DST_GC_MIN (HZ/10)
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#define DST_GC_INC (HZ/2)
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#define DST_GC_MAX (120*HZ)
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/* Each dst_entry has reference count and sits in some parent list(s).
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* When it is removed from parent list, it is "freed" (dst_free).
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* After this it enters dead state (dst->obsolete > 0) and if its refcnt
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* is zero, it can be destroyed immediately, otherwise it is added
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* to gc list and garbage collector periodically checks the refcnt.
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*/
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struct sk_buff;
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struct dst_entry {
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struct net_device *dev;
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struct rcu_head rcu_head;
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struct dst_entry *child;
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struct dst_ops *ops;
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unsigned long _metrics;
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unsigned long expires;
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struct dst_entry *path;
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struct dst_entry *from;
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#ifdef CONFIG_XFRM
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struct xfrm_state *xfrm;
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#else
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void *__pad1;
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#endif
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int (*input)(struct sk_buff *);
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int (*output)(struct net *net, struct sock *sk, struct sk_buff *skb);
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unsigned short flags;
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#define DST_HOST 0x0001
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#define DST_NOXFRM 0x0002
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#define DST_NOPOLICY 0x0004
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#define DST_NOCOUNT 0x0008
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#define DST_FAKE_RTABLE 0x0010
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#define DST_XFRM_TUNNEL 0x0020
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#define DST_XFRM_QUEUE 0x0040
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#define DST_METADATA 0x0080
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short error;
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/* A non-zero value of dst->obsolete forces by-hand validation
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* of the route entry. Positive values are set by the generic
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* dst layer to indicate that the entry has been forcefully
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* destroyed.
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*
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* Negative values are used by the implementation layer code to
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* force invocation of the dst_ops->check() method.
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*/
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short obsolete;
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#define DST_OBSOLETE_NONE 0
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#define DST_OBSOLETE_DEAD 2
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#define DST_OBSOLETE_FORCE_CHK -1
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#define DST_OBSOLETE_KILL -2
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unsigned short header_len; /* more space at head required */
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unsigned short trailer_len; /* space to reserve at tail */
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unsigned short __pad3;
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#ifdef CONFIG_IP_ROUTE_CLASSID
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__u32 tclassid;
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#else
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__u32 __pad2;
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#endif
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#ifdef CONFIG_64BIT
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/*
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* Align __refcnt to a 64 bytes alignment
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* (L1_CACHE_SIZE would be too much)
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*/
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long __pad_to_align_refcnt[2];
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#endif
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/*
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* __refcnt wants to be on a different cache line from
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* input/output/ops or performance tanks badly
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*/
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atomic_t __refcnt; /* client references */
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int __use;
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unsigned long lastuse;
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struct lwtunnel_state *lwtstate;
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union {
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struct dst_entry *next;
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struct rtable __rcu *rt_next;
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struct rt6_info __rcu *rt6_next;
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struct dn_route __rcu *dn_next;
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};
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};
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struct dst_metrics {
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u32 metrics[RTAX_MAX];
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refcount_t refcnt;
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};
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extern const struct dst_metrics dst_default_metrics;
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u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old);
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#define DST_METRICS_READ_ONLY 0x1UL
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#define DST_METRICS_REFCOUNTED 0x2UL
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#define DST_METRICS_FLAGS 0x3UL
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#define __DST_METRICS_PTR(Y) \
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((u32 *)((Y) & ~DST_METRICS_FLAGS))
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#define DST_METRICS_PTR(X) __DST_METRICS_PTR((X)->_metrics)
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static inline bool dst_metrics_read_only(const struct dst_entry *dst)
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{
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return dst->_metrics & DST_METRICS_READ_ONLY;
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}
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void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old);
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static inline void dst_destroy_metrics_generic(struct dst_entry *dst)
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{
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unsigned long val = dst->_metrics;
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if (!(val & DST_METRICS_READ_ONLY))
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__dst_destroy_metrics_generic(dst, val);
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}
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static inline u32 *dst_metrics_write_ptr(struct dst_entry *dst)
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{
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unsigned long p = dst->_metrics;
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BUG_ON(!p);
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if (p & DST_METRICS_READ_ONLY)
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return dst->ops->cow_metrics(dst, p);
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return __DST_METRICS_PTR(p);
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}
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/* This may only be invoked before the entry has reached global
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* visibility.
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*/
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static inline void dst_init_metrics(struct dst_entry *dst,
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const u32 *src_metrics,
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bool read_only)
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{
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dst->_metrics = ((unsigned long) src_metrics) |
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(read_only ? DST_METRICS_READ_ONLY : 0);
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}
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static inline void dst_copy_metrics(struct dst_entry *dest, const struct dst_entry *src)
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{
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u32 *dst_metrics = dst_metrics_write_ptr(dest);
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if (dst_metrics) {
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u32 *src_metrics = DST_METRICS_PTR(src);
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memcpy(dst_metrics, src_metrics, RTAX_MAX * sizeof(u32));
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}
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}
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static inline u32 *dst_metrics_ptr(struct dst_entry *dst)
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{
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return DST_METRICS_PTR(dst);
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}
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static inline u32
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dst_metric_raw(const struct dst_entry *dst, const int metric)
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{
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u32 *p = DST_METRICS_PTR(dst);
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return p[metric-1];
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}
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static inline u32
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dst_metric(const struct dst_entry *dst, const int metric)
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{
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WARN_ON_ONCE(metric == RTAX_HOPLIMIT ||
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metric == RTAX_ADVMSS ||
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metric == RTAX_MTU);
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return dst_metric_raw(dst, metric);
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}
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static inline u32
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dst_metric_advmss(const struct dst_entry *dst)
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{
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u32 advmss = dst_metric_raw(dst, RTAX_ADVMSS);
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if (!advmss)
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advmss = dst->ops->default_advmss(dst);
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return advmss;
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}
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static inline void dst_metric_set(struct dst_entry *dst, int metric, u32 val)
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{
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u32 *p = dst_metrics_write_ptr(dst);
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if (p)
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p[metric-1] = val;
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}
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/* Kernel-internal feature bits that are unallocated in user space. */
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#define DST_FEATURE_ECN_CA (1 << 31)
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#define DST_FEATURE_MASK (DST_FEATURE_ECN_CA)
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#define DST_FEATURE_ECN_MASK (DST_FEATURE_ECN_CA | RTAX_FEATURE_ECN)
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static inline u32
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dst_feature(const struct dst_entry *dst, u32 feature)
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{
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return dst_metric(dst, RTAX_FEATURES) & feature;
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}
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static inline u32 dst_mtu(const struct dst_entry *dst)
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{
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return dst->ops->mtu(dst);
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}
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/* RTT metrics are stored in milliseconds for user ABI, but used as jiffies */
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static inline unsigned long dst_metric_rtt(const struct dst_entry *dst, int metric)
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{
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return msecs_to_jiffies(dst_metric(dst, metric));
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}
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static inline u32
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dst_allfrag(const struct dst_entry *dst)
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{
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int ret = dst_feature(dst, RTAX_FEATURE_ALLFRAG);
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return ret;
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}
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static inline int
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dst_metric_locked(const struct dst_entry *dst, int metric)
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{
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return dst_metric(dst, RTAX_LOCK) & (1<<metric);
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}
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static inline void dst_hold(struct dst_entry *dst)
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{
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/*
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* If your kernel compilation stops here, please check
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* __pad_to_align_refcnt declaration in struct dst_entry
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*/
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BUILD_BUG_ON(offsetof(struct dst_entry, __refcnt) & 63);
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WARN_ON(atomic_inc_not_zero(&dst->__refcnt) == 0);
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}
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static inline void dst_use(struct dst_entry *dst, unsigned long time)
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{
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dst_hold(dst);
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dst->__use++;
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dst->lastuse = time;
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}
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static inline void dst_use_noref(struct dst_entry *dst, unsigned long time)
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{
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dst->__use++;
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dst->lastuse = time;
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}
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static inline struct dst_entry *dst_clone(struct dst_entry *dst)
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{
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if (dst)
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dst_hold(dst);
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return dst;
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}
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void dst_release(struct dst_entry *dst);
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void dst_release_immediate(struct dst_entry *dst);
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static inline void refdst_drop(unsigned long refdst)
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{
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if (!(refdst & SKB_DST_NOREF))
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dst_release((struct dst_entry *)(refdst & SKB_DST_PTRMASK));
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}
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/**
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* skb_dst_drop - drops skb dst
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* @skb: buffer
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*
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* Drops dst reference count if a reference was taken.
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*/
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static inline void skb_dst_drop(struct sk_buff *skb)
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{
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if (skb->_skb_refdst) {
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refdst_drop(skb->_skb_refdst);
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skb->_skb_refdst = 0UL;
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}
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}
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static inline void __skb_dst_copy(struct sk_buff *nskb, unsigned long refdst)
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{
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nskb->_skb_refdst = refdst;
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if (!(nskb->_skb_refdst & SKB_DST_NOREF))
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dst_clone(skb_dst(nskb));
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}
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static inline void skb_dst_copy(struct sk_buff *nskb, const struct sk_buff *oskb)
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{
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__skb_dst_copy(nskb, oskb->_skb_refdst);
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}
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/**
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* dst_hold_safe - Take a reference on a dst if possible
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* @dst: pointer to dst entry
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*
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* This helper returns false if it could not safely
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* take a reference on a dst.
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*/
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static inline bool dst_hold_safe(struct dst_entry *dst)
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{
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return atomic_inc_not_zero(&dst->__refcnt);
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}
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/**
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* skb_dst_force - makes sure skb dst is refcounted
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* @skb: buffer
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*
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* If dst is not yet refcounted and not destroyed, grab a ref on it.
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*/
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static inline void skb_dst_force(struct sk_buff *skb)
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{
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if (skb_dst_is_noref(skb)) {
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struct dst_entry *dst = skb_dst(skb);
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WARN_ON(!rcu_read_lock_held());
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if (!dst_hold_safe(dst))
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dst = NULL;
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skb->_skb_refdst = (unsigned long)dst;
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}
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}
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/**
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* __skb_tunnel_rx - prepare skb for rx reinsert
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* @skb: buffer
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* @dev: tunnel device
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* @net: netns for packet i/o
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*
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* After decapsulation, packet is going to re-enter (netif_rx()) our stack,
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* so make some cleanups. (no accounting done)
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*/
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static inline void __skb_tunnel_rx(struct sk_buff *skb, struct net_device *dev,
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struct net *net)
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{
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skb->dev = dev;
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/*
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* Clear hash so that we can recalulate the hash for the
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* encapsulated packet, unless we have already determine the hash
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* over the L4 4-tuple.
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*/
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skb_clear_hash_if_not_l4(skb);
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skb_set_queue_mapping(skb, 0);
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skb_scrub_packet(skb, !net_eq(net, dev_net(dev)));
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}
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/**
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* skb_tunnel_rx - prepare skb for rx reinsert
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* @skb: buffer
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* @dev: tunnel device
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*
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* After decapsulation, packet is going to re-enter (netif_rx()) our stack,
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* so make some cleanups, and perform accounting.
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* Note: this accounting is not SMP safe.
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*/
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static inline void skb_tunnel_rx(struct sk_buff *skb, struct net_device *dev,
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struct net *net)
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{
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/* TODO : stats should be SMP safe */
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dev->stats.rx_packets++;
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dev->stats.rx_bytes += skb->len;
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__skb_tunnel_rx(skb, dev, net);
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}
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static inline u32 dst_tclassid(const struct sk_buff *skb)
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{
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#ifdef CONFIG_IP_ROUTE_CLASSID
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const struct dst_entry *dst;
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dst = skb_dst(skb);
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if (dst)
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return dst->tclassid;
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#endif
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return 0;
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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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static inline int dst_discard(struct sk_buff *skb)
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{
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return dst_discard_out(&init_net, skb->sk, skb);
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}
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void *dst_alloc(struct dst_ops *ops, struct net_device *dev, int initial_ref,
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int initial_obsolete, unsigned short flags);
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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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struct dst_entry *dst_destroy(struct dst_entry *dst);
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void dst_dev_put(struct dst_entry *dst);
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static inline void dst_confirm(struct dst_entry *dst)
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{
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}
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static inline struct neighbour *dst_neigh_lookup(const struct dst_entry *dst, const void *daddr)
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{
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struct neighbour *n = dst->ops->neigh_lookup(dst, NULL, daddr);
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return IS_ERR(n) ? NULL : n;
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}
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static inline struct neighbour *dst_neigh_lookup_skb(const struct dst_entry *dst,
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struct sk_buff *skb)
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{
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struct neighbour *n = dst->ops->neigh_lookup(dst, skb, NULL);
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return IS_ERR(n) ? NULL : n;
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}
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static inline void dst_confirm_neigh(const struct dst_entry *dst,
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const void *daddr)
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{
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if (dst->ops->confirm_neigh)
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dst->ops->confirm_neigh(dst, daddr);
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}
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static inline void dst_link_failure(struct sk_buff *skb)
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{
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struct dst_entry *dst = skb_dst(skb);
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if (dst && dst->ops && dst->ops->link_failure)
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dst->ops->link_failure(skb);
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}
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static inline void dst_set_expires(struct dst_entry *dst, int timeout)
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{
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unsigned long expires = jiffies + timeout;
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if (expires == 0)
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expires = 1;
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if (dst->expires == 0 || time_before(expires, dst->expires))
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dst->expires = expires;
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}
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/* Output packet to network from transport. */
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static inline int dst_output(struct net *net, struct sock *sk, struct sk_buff *skb)
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{
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return skb_dst(skb)->output(net, sk, skb);
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}
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/* Input packet from network to transport. */
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static inline int dst_input(struct sk_buff *skb)
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{
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return skb_dst(skb)->input(skb);
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}
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static inline struct dst_entry *dst_check(struct dst_entry *dst, u32 cookie)
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{
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if (dst->obsolete)
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dst = dst->ops->check(dst, cookie);
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return dst;
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}
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/* Flags for xfrm_lookup flags argument. */
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enum {
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XFRM_LOOKUP_ICMP = 1 << 0,
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XFRM_LOOKUP_QUEUE = 1 << 1,
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XFRM_LOOKUP_KEEP_DST_REF = 1 << 2,
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};
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struct flowi;
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#ifndef CONFIG_XFRM
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static inline struct dst_entry *xfrm_lookup(struct net *net,
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struct dst_entry *dst_orig,
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const struct flowi *fl,
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const struct sock *sk,
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|
int flags)
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|
{
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|
return dst_orig;
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}
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|
|
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static inline struct dst_entry *xfrm_lookup_route(struct net *net,
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|
struct dst_entry *dst_orig,
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|
const struct flowi *fl,
|
|
const struct sock *sk,
|
|
int flags)
|
|
{
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|
return dst_orig;
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|
}
|
|
|
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static inline struct xfrm_state *dst_xfrm(const struct dst_entry *dst)
|
|
{
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|
return NULL;
|
|
}
|
|
|
|
#else
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|
struct dst_entry *xfrm_lookup(struct net *net, struct dst_entry *dst_orig,
|
|
const struct flowi *fl, const struct sock *sk,
|
|
int flags);
|
|
|
|
struct dst_entry *xfrm_lookup_route(struct net *net, struct dst_entry *dst_orig,
|
|
const struct flowi *fl, const struct sock *sk,
|
|
int flags);
|
|
|
|
/* skb attached with this dst needs transformation if dst->xfrm is valid */
|
|
static inline struct xfrm_state *dst_xfrm(const struct dst_entry *dst)
|
|
{
|
|
return dst->xfrm;
|
|
}
|
|
#endif
|
|
|
|
#endif /* _NET_DST_H */
|