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linux-stable/include/net/dst.h
Wei Wang 5f56f409b5 net: introduce DST_NOGC in dst_release() to destroy dst based on refcnt 
The current mechanism of freeing dst is a bit complicated. dst has its
ref count and when user grabs the reference to the dst, the ref count is
properly taken in most cases except in IPv4/IPv6/decnet/xfrm routing
code due to some historic reasons.

If the reference to dst is always taken properly, we should be able to
simplify the logic in dst_release() to destroy dst when dst->__refcnt
drops from 1 to 0. And this should be the only condition to determine
if we can call dst_destroy().
And as dst is always ref counted, there is no need for a dst garbage
list to hold the dst entries that already get removed by the routing
code but are still held by other users. And the task to periodically
check the list to free dst if ref count become 0 is also not needed
anymore.

This patch introduces a temporary flag DST_NOGC(no garbage collector).
If it is set in the dst, dst_release() will call dst_destroy() when
dst->__refcnt drops to 0. dst_hold_safe() will also check for this flag
and do atomic_inc_not_zero() similar as DST_NOCACHE to avoid double free
issue.
This temporary flag is mainly used so that we can make the transition
component by component without breaking other parts.
This flag will be removed after all components are properly transitioned.

This patch also introduces a new function dst_release_immediate() which
destroys dst without waiting on the rcu when refcnt drops to 0. It will
be used in later patches.

Follow-up patches will correct all the places to properly take ref count
on dst and mark DST_NOGC. dst_release() or dst_release_immediate() will
be used to release the dst instead of dst_free() and its related
functions.
And final clean-up patch will remove the DST_NOGC flag.

Signed-off-by: Wei Wang <weiwan@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2017-06-17 22:53:59 -04:00

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/*
* net/dst.h Protocol independent destination cache definitions.
*
* Authors: Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
*
*/
#ifndef _NET_DST_H
#define _NET_DST_H
#include <net/dst_ops.h>
#include <linux/netdevice.h>
#include <linux/rtnetlink.h>
#include <linux/rcupdate.h>
#include <linux/bug.h>
#include <linux/jiffies.h>
#include <net/neighbour.h>
#include <asm/processor.h>
#define DST_GC_MIN (HZ/10)
#define DST_GC_INC (HZ/2)
#define DST_GC_MAX (120*HZ)
/* Each dst_entry has reference count and sits in some parent list(s).
* When it is removed from parent list, it is "freed" (dst_free).
* After this it enters dead state (dst->obsolete > 0) and if its refcnt
* is zero, it can be destroyed immediately, otherwise it is added
* to gc list and garbage collector periodically checks the refcnt.
*/
struct sk_buff;
struct dst_entry {
struct net_device *dev;
struct rcu_head rcu_head;
struct dst_entry *child;
struct dst_ops *ops;
unsigned long _metrics;
unsigned long expires;
struct dst_entry *path;
struct dst_entry *from;
#ifdef CONFIG_XFRM
struct xfrm_state *xfrm;
#else
void *__pad1;
#endif
int (*input)(struct sk_buff *);
int (*output)(struct net *net, struct sock *sk, struct sk_buff *skb);
unsigned short flags;
#define DST_HOST 0x0001
#define DST_NOXFRM 0x0002
#define DST_NOPOLICY 0x0004
#define DST_NOHASH 0x0008
#define DST_NOCACHE 0x0010
#define DST_NOCOUNT 0x0020
#define DST_FAKE_RTABLE 0x0040
#define DST_XFRM_TUNNEL 0x0080
#define DST_XFRM_QUEUE 0x0100
#define DST_METADATA 0x0200
#define DST_NOGC 0x0400
short error;
/* A non-zero value of dst->obsolete forces by-hand validation
* of the route entry. Positive values are set by the generic
* dst layer to indicate that the entry has been forcefully
* destroyed.
*
* Negative values are used by the implementation layer code to
* force invocation of the dst_ops->check() method.
*/
short obsolete;
#define DST_OBSOLETE_NONE 0
#define DST_OBSOLETE_DEAD 2
#define DST_OBSOLETE_FORCE_CHK -1
#define DST_OBSOLETE_KILL -2
unsigned short header_len; /* more space at head required */
unsigned short trailer_len; /* space to reserve at tail */
unsigned short __pad3;
#ifdef CONFIG_IP_ROUTE_CLASSID
__u32 tclassid;
#else
__u32 __pad2;
#endif
#ifdef CONFIG_64BIT
/*
* Align __refcnt to a 64 bytes alignment
* (L1_CACHE_SIZE would be too much)
*/
long __pad_to_align_refcnt[2];
#endif
/*
* __refcnt wants to be on a different cache line from
* input/output/ops or performance tanks badly
*/
atomic_t __refcnt; /* client references */
int __use;
unsigned long lastuse;
struct lwtunnel_state *lwtstate;
union {
struct dst_entry *next;
struct rtable __rcu *rt_next;
struct rt6_info *rt6_next;
struct dn_route __rcu *dn_next;
};
};
struct dst_metrics {
u32 metrics[RTAX_MAX];
atomic_t refcnt;
};
extern const struct dst_metrics dst_default_metrics;
u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old);
#define DST_METRICS_READ_ONLY 0x1UL
#define DST_METRICS_REFCOUNTED 0x2UL
#define DST_METRICS_FLAGS 0x3UL
#define __DST_METRICS_PTR(Y) \
((u32 *)((Y) & ~DST_METRICS_FLAGS))
#define DST_METRICS_PTR(X) __DST_METRICS_PTR((X)->_metrics)
static inline bool dst_metrics_read_only(const struct dst_entry *dst)
{
return dst->_metrics & DST_METRICS_READ_ONLY;
}
void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old);
static inline void dst_destroy_metrics_generic(struct dst_entry *dst)
{
unsigned long val = dst->_metrics;
if (!(val & DST_METRICS_READ_ONLY))
__dst_destroy_metrics_generic(dst, val);
}
static inline u32 *dst_metrics_write_ptr(struct dst_entry *dst)
{
unsigned long p = dst->_metrics;
BUG_ON(!p);
if (p & DST_METRICS_READ_ONLY)
return dst->ops->cow_metrics(dst, p);
return __DST_METRICS_PTR(p);
}
/* This may only be invoked before the entry has reached global
* visibility.
*/
static inline void dst_init_metrics(struct dst_entry *dst,
const u32 *src_metrics,
bool read_only)
{
dst->_metrics = ((unsigned long) src_metrics) |
(read_only ? DST_METRICS_READ_ONLY : 0);
}
static inline void dst_copy_metrics(struct dst_entry *dest, const struct dst_entry *src)
{
u32 *dst_metrics = dst_metrics_write_ptr(dest);
if (dst_metrics) {
u32 *src_metrics = DST_METRICS_PTR(src);
memcpy(dst_metrics, src_metrics, RTAX_MAX * sizeof(u32));
}
}
static inline u32 *dst_metrics_ptr(struct dst_entry *dst)
{
return DST_METRICS_PTR(dst);
}
static inline u32
dst_metric_raw(const struct dst_entry *dst, const int metric)
{
u32 *p = DST_METRICS_PTR(dst);
return p[metric-1];
}
static inline u32
dst_metric(const struct dst_entry *dst, const int metric)
{
WARN_ON_ONCE(metric == RTAX_HOPLIMIT ||
metric == RTAX_ADVMSS ||
metric == RTAX_MTU);
return dst_metric_raw(dst, metric);
}
static inline u32
dst_metric_advmss(const struct dst_entry *dst)
{
u32 advmss = dst_metric_raw(dst, RTAX_ADVMSS);
if (!advmss)
advmss = dst->ops->default_advmss(dst);
return advmss;
}
static inline void dst_metric_set(struct dst_entry *dst, int metric, u32 val)
{
u32 *p = dst_metrics_write_ptr(dst);
if (p)
p[metric-1] = val;
}
/* Kernel-internal feature bits that are unallocated in user space. */
#define DST_FEATURE_ECN_CA (1 << 31)
#define DST_FEATURE_MASK (DST_FEATURE_ECN_CA)
#define DST_FEATURE_ECN_MASK (DST_FEATURE_ECN_CA | RTAX_FEATURE_ECN)
static inline u32
dst_feature(const struct dst_entry *dst, u32 feature)
{
return dst_metric(dst, RTAX_FEATURES) & feature;
}
static inline u32 dst_mtu(const struct dst_entry *dst)
{
return dst->ops->mtu(dst);
}
/* RTT metrics are stored in milliseconds for user ABI, but used as jiffies */
static inline unsigned long dst_metric_rtt(const struct dst_entry *dst, int metric)
{
return msecs_to_jiffies(dst_metric(dst, metric));
}
static inline u32
dst_allfrag(const struct dst_entry *dst)
{
int ret = dst_feature(dst, RTAX_FEATURE_ALLFRAG);
return ret;
}
static inline int
dst_metric_locked(const struct dst_entry *dst, int metric)
{
return dst_metric(dst, RTAX_LOCK) & (1<<metric);
}
static inline void dst_hold(struct dst_entry *dst)
{
/*
* If your kernel compilation stops here, please check
* __pad_to_align_refcnt declaration in struct dst_entry
*/
BUILD_BUG_ON(offsetof(struct dst_entry, __refcnt) & 63);
atomic_inc(&dst->__refcnt);
}
static inline void dst_use(struct dst_entry *dst, unsigned long time)
{
dst_hold(dst);
dst->__use++;
dst->lastuse = time;
}
static inline void dst_use_noref(struct dst_entry *dst, unsigned long time)
{
dst->__use++;
dst->lastuse = time;
}
static inline struct dst_entry *dst_clone(struct dst_entry *dst)
{
if (dst)
atomic_inc(&dst->__refcnt);
return dst;
}
void dst_release(struct dst_entry *dst);
void dst_release_immediate(struct dst_entry *dst);
static inline void refdst_drop(unsigned long refdst)
{
if (!(refdst & SKB_DST_NOREF))
dst_release((struct dst_entry *)(refdst & SKB_DST_PTRMASK));
}
/**
* skb_dst_drop - drops skb dst
* @skb: buffer
*
* Drops dst reference count if a reference was taken.
*/
static inline void skb_dst_drop(struct sk_buff *skb)
{
if (skb->_skb_refdst) {
refdst_drop(skb->_skb_refdst);
skb->_skb_refdst = 0UL;
}
}
static inline void __skb_dst_copy(struct sk_buff *nskb, unsigned long refdst)
{
nskb->_skb_refdst = refdst;
if (!(nskb->_skb_refdst & SKB_DST_NOREF))
dst_clone(skb_dst(nskb));
}
static inline void skb_dst_copy(struct sk_buff *nskb, const struct sk_buff *oskb)
{
__skb_dst_copy(nskb, oskb->_skb_refdst);
}
/**
* skb_dst_force - makes sure skb dst is refcounted
* @skb: buffer
*
* If dst is not yet refcounted, let's do it
*/
static inline void skb_dst_force(struct sk_buff *skb)
{
if (skb_dst_is_noref(skb)) {
WARN_ON(!rcu_read_lock_held());
skb->_skb_refdst &= ~SKB_DST_NOREF;
dst_clone(skb_dst(skb));
}
}
/**
* dst_hold_safe - Take a reference on a dst if possible
* @dst: pointer to dst entry
*
* This helper returns false if it could not safely
* take a reference on a dst.
*/
static inline bool dst_hold_safe(struct dst_entry *dst)
{
if (dst->flags & (DST_NOCACHE | DST_NOGC))
return atomic_inc_not_zero(&dst->__refcnt);
dst_hold(dst);
return true;
}
/**
* skb_dst_force_safe - makes sure skb dst is refcounted
* @skb: buffer
*
* If dst is not yet refcounted and not destroyed, grab a ref on it.
*/
static inline void skb_dst_force_safe(struct sk_buff *skb)
{
if (skb_dst_is_noref(skb)) {
struct dst_entry *dst = skb_dst(skb);
if (!dst_hold_safe(dst))
dst = NULL;
skb->_skb_refdst = (unsigned long)dst;
}
}
/**
* __skb_tunnel_rx - prepare skb for rx reinsert
* @skb: buffer
* @dev: tunnel device
* @net: netns for packet i/o
*
* After decapsulation, packet is going to re-enter (netif_rx()) our stack,
* so make some cleanups. (no accounting done)
*/
static inline void __skb_tunnel_rx(struct sk_buff *skb, struct net_device *dev,
struct net *net)
{
skb->dev = dev;
/*
* Clear hash so that we can recalulate the hash for the
* encapsulated packet, unless we have already determine the hash
* over the L4 4-tuple.
*/
skb_clear_hash_if_not_l4(skb);
skb_set_queue_mapping(skb, 0);
skb_scrub_packet(skb, !net_eq(net, dev_net(dev)));
}
/**
* skb_tunnel_rx - prepare skb for rx reinsert
* @skb: buffer
* @dev: tunnel device
*
* After decapsulation, packet is going to re-enter (netif_rx()) our stack,
* so make some cleanups, and perform accounting.
* Note: this accounting is not SMP safe.
*/
static inline void skb_tunnel_rx(struct sk_buff *skb, struct net_device *dev,
struct net *net)
{
/* TODO : stats should be SMP safe */
dev->stats.rx_packets++;
dev->stats.rx_bytes += skb->len;
__skb_tunnel_rx(skb, dev, net);
}
static inline u32 dst_tclassid(const struct sk_buff *skb)
{
#ifdef CONFIG_IP_ROUTE_CLASSID
const struct dst_entry *dst;
dst = skb_dst(skb);
if (dst)
return dst->tclassid;
#endif
return 0;
}
int dst_discard_out(struct net *net, struct sock *sk, struct sk_buff *skb);
static inline int dst_discard(struct sk_buff *skb)
{
return dst_discard_out(&init_net, skb->sk, skb);
}
void *dst_alloc(struct dst_ops *ops, struct net_device *dev, int initial_ref,
int initial_obsolete, unsigned short flags);
void dst_init(struct dst_entry *dst, struct dst_ops *ops,
struct net_device *dev, int initial_ref, int initial_obsolete,
unsigned short flags);
void __dst_free(struct dst_entry *dst);
struct dst_entry *dst_destroy(struct dst_entry *dst);
static inline void dst_free(struct dst_entry *dst)
{
if (dst->obsolete > 0)
return;
if (!atomic_read(&dst->__refcnt)) {
dst = dst_destroy(dst);
if (!dst)
return;
}
__dst_free(dst);
}
static inline void dst_rcu_free(struct rcu_head *head)
{
struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
dst_free(dst);
}
static inline void dst_confirm(struct dst_entry *dst)
{
}
static inline struct neighbour *dst_neigh_lookup(const struct dst_entry *dst, const void *daddr)
{
struct neighbour *n = dst->ops->neigh_lookup(dst, NULL, daddr);
return IS_ERR(n) ? NULL : n;
}
static inline struct neighbour *dst_neigh_lookup_skb(const struct dst_entry *dst,
struct sk_buff *skb)
{
struct neighbour *n = dst->ops->neigh_lookup(dst, skb, NULL);
return IS_ERR(n) ? NULL : n;
}
static inline void dst_confirm_neigh(const struct dst_entry *dst,
const void *daddr)
{
if (dst->ops->confirm_neigh)
dst->ops->confirm_neigh(dst, daddr);
}
static inline void dst_link_failure(struct sk_buff *skb)
{
struct dst_entry *dst = skb_dst(skb);
if (dst && dst->ops && dst->ops->link_failure)
dst->ops->link_failure(skb);
}
static inline void dst_set_expires(struct dst_entry *dst, int timeout)
{
unsigned long expires = jiffies + timeout;
if (expires == 0)
expires = 1;
if (dst->expires == 0 || time_before(expires, dst->expires))
dst->expires = expires;
}
/* Output packet to network from transport. */
static inline int dst_output(struct net *net, struct sock *sk, struct sk_buff *skb)
{
return skb_dst(skb)->output(net, sk, skb);
}
/* Input packet from network to transport. */
static inline int dst_input(struct sk_buff *skb)
{
return skb_dst(skb)->input(skb);
}
static inline struct dst_entry *dst_check(struct dst_entry *dst, u32 cookie)
{
if (dst->obsolete)
dst = dst->ops->check(dst, cookie);
return dst;
}
void dst_subsys_init(void);
/* Flags for xfrm_lookup flags argument. */
enum {
XFRM_LOOKUP_ICMP = 1 << 0,
XFRM_LOOKUP_QUEUE = 1 << 1,
XFRM_LOOKUP_KEEP_DST_REF = 1 << 2,
};
struct flowi;
#ifndef CONFIG_XFRM
static inline struct dst_entry *xfrm_lookup(struct net *net,
struct dst_entry *dst_orig,
const struct flowi *fl,
const struct sock *sk,
int flags)
{
return dst_orig;
}
static inline struct dst_entry *xfrm_lookup_route(struct net *net,
struct dst_entry *dst_orig,
const struct flowi *fl,
const struct sock *sk,
int flags)
{
return dst_orig;
}
static inline struct xfrm_state *dst_xfrm(const struct dst_entry *dst)
{
return NULL;
}
#else
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 */
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