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inetpeer: __rcu annotations
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Adds __rcu annotations to inetpeer
	(struct inet_peer)->avl_left
	(struct inet_peer)->avl_right

This is a tedious cleanup, but removes one smp_wmb() from link_to_pool()
since we now use more self documenting rcu_assign_pointer().

Note the use of RCU_INIT_POINTER() instead of rcu_assign_pointer() in
all cases we dont need a memory barrier.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Eric Dumazet authored and David S. Miller committed Oct 27, 2010
1 parent 7a2b03c commit b914c4e
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Showing 2 changed files with 81 additions and 59 deletions.
2 changes: 1 addition & 1 deletion include/net/inetpeer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@

struct inet_peer {
/* group together avl_left,avl_right,v4daddr to speedup lookups */
struct inet_peer *avl_left, *avl_right;
struct inet_peer __rcu *avl_left, *avl_right;
__be32 v4daddr; /* peer's address */
__u32 avl_height;
struct list_head unused;
Expand Down
138 changes: 80 additions & 58 deletions net/ipv4/inetpeer.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -72,18 +72,19 @@ static struct kmem_cache *peer_cachep __read_mostly;
#define node_height(x) x->avl_height

#define peer_avl_empty ((struct inet_peer *)&peer_fake_node)
#define peer_avl_empty_rcu ((struct inet_peer __rcu __force *)&peer_fake_node)
static const struct inet_peer peer_fake_node = {
.avl_left = peer_avl_empty,
.avl_right = peer_avl_empty,
.avl_left = peer_avl_empty_rcu,
.avl_right = peer_avl_empty_rcu,
.avl_height = 0
};

static struct {
struct inet_peer *root;
struct inet_peer __rcu *root;
spinlock_t lock;
int total;
} peers = {
.root = peer_avl_empty,
.root = peer_avl_empty_rcu,
.lock = __SPIN_LOCK_UNLOCKED(peers.lock),
.total = 0,
};
Expand Down Expand Up @@ -156,19 +157,23 @@ static void unlink_from_unused(struct inet_peer *p)
*/
#define lookup(_daddr, _stack) \
({ \
struct inet_peer *u, **v; \
struct inet_peer *u; \
struct inet_peer __rcu **v; \
\
stackptr = _stack; \
*stackptr++ = &peers.root; \
for (u = peers.root; u != peer_avl_empty; ) { \
for (u = rcu_dereference_protected(peers.root, \
lockdep_is_held(&peers.lock)); \
u != peer_avl_empty; ) { \
if (_daddr == u->v4daddr) \
break; \
if ((__force __u32)_daddr < (__force __u32)u->v4daddr) \
v = &u->avl_left; \
else \
v = &u->avl_right; \
*stackptr++ = v; \
u = *v; \
u = rcu_dereference_protected(*v, \
lockdep_is_held(&peers.lock)); \
} \
u; \
})
Expand Down Expand Up @@ -209,13 +214,17 @@ static struct inet_peer *lookup_rcu_bh(__be32 daddr)
/* Called with local BH disabled and the pool lock held. */
#define lookup_rightempty(start) \
({ \
struct inet_peer *u, **v; \
struct inet_peer *u; \
struct inet_peer __rcu **v; \
*stackptr++ = &start->avl_left; \
v = &start->avl_left; \
for (u = *v; u->avl_right != peer_avl_empty; ) { \
for (u = rcu_dereference_protected(*v, \
lockdep_is_held(&peers.lock)); \
u->avl_right != peer_avl_empty_rcu; ) { \
v = &u->avl_right; \
*stackptr++ = v; \
u = *v; \
u = rcu_dereference_protected(*v, \
lockdep_is_held(&peers.lock)); \
} \
u; \
})
Expand All @@ -224,74 +233,86 @@ static struct inet_peer *lookup_rcu_bh(__be32 daddr)
* Variable names are the proof of operation correctness.
* Look into mm/map_avl.c for more detail description of the ideas.
*/
static void peer_avl_rebalance(struct inet_peer **stack[],
struct inet_peer ***stackend)
static void peer_avl_rebalance(struct inet_peer __rcu **stack[],
struct inet_peer __rcu ***stackend)
{
struct inet_peer **nodep, *node, *l, *r;
struct inet_peer __rcu **nodep;
struct inet_peer *node, *l, *r;
int lh, rh;

while (stackend > stack) {
nodep = *--stackend;
node = *nodep;
l = node->avl_left;
r = node->avl_right;
node = rcu_dereference_protected(*nodep,
lockdep_is_held(&peers.lock));
l = rcu_dereference_protected(node->avl_left,
lockdep_is_held(&peers.lock));
r = rcu_dereference_protected(node->avl_right,
lockdep_is_held(&peers.lock));
lh = node_height(l);
rh = node_height(r);
if (lh > rh + 1) { /* l: RH+2 */
struct inet_peer *ll, *lr, *lrl, *lrr;
int lrh;
ll = l->avl_left;
lr = l->avl_right;
ll = rcu_dereference_protected(l->avl_left,
lockdep_is_held(&peers.lock));
lr = rcu_dereference_protected(l->avl_right,
lockdep_is_held(&peers.lock));
lrh = node_height(lr);
if (lrh <= node_height(ll)) { /* ll: RH+1 */
node->avl_left = lr; /* lr: RH or RH+1 */
node->avl_right = r; /* r: RH */
RCU_INIT_POINTER(node->avl_left, lr); /* lr: RH or RH+1 */
RCU_INIT_POINTER(node->avl_right, r); /* r: RH */
node->avl_height = lrh + 1; /* RH+1 or RH+2 */
l->avl_left = ll; /* ll: RH+1 */
l->avl_right = node; /* node: RH+1 or RH+2 */
RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH+1 */
RCU_INIT_POINTER(l->avl_right, node); /* node: RH+1 or RH+2 */
l->avl_height = node->avl_height + 1;
*nodep = l;
RCU_INIT_POINTER(*nodep, l);
} else { /* ll: RH, lr: RH+1 */
lrl = lr->avl_left; /* lrl: RH or RH-1 */
lrr = lr->avl_right; /* lrr: RH or RH-1 */
node->avl_left = lrr; /* lrr: RH or RH-1 */
node->avl_right = r; /* r: RH */
lrl = rcu_dereference_protected(lr->avl_left,
lockdep_is_held(&peers.lock)); /* lrl: RH or RH-1 */
lrr = rcu_dereference_protected(lr->avl_right,
lockdep_is_held(&peers.lock)); /* lrr: RH or RH-1 */
RCU_INIT_POINTER(node->avl_left, lrr); /* lrr: RH or RH-1 */
RCU_INIT_POINTER(node->avl_right, r); /* r: RH */
node->avl_height = rh + 1; /* node: RH+1 */
l->avl_left = ll; /* ll: RH */
l->avl_right = lrl; /* lrl: RH or RH-1 */
RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH */
RCU_INIT_POINTER(l->avl_right, lrl); /* lrl: RH or RH-1 */
l->avl_height = rh + 1; /* l: RH+1 */
lr->avl_left = l; /* l: RH+1 */
lr->avl_right = node; /* node: RH+1 */
RCU_INIT_POINTER(lr->avl_left, l); /* l: RH+1 */
RCU_INIT_POINTER(lr->avl_right, node); /* node: RH+1 */
lr->avl_height = rh + 2;
*nodep = lr;
RCU_INIT_POINTER(*nodep, lr);
}
} else if (rh > lh + 1) { /* r: LH+2 */
struct inet_peer *rr, *rl, *rlr, *rll;
int rlh;
rr = r->avl_right;
rl = r->avl_left;
rr = rcu_dereference_protected(r->avl_right,
lockdep_is_held(&peers.lock));
rl = rcu_dereference_protected(r->avl_left,
lockdep_is_held(&peers.lock));
rlh = node_height(rl);
if (rlh <= node_height(rr)) { /* rr: LH+1 */
node->avl_right = rl; /* rl: LH or LH+1 */
node->avl_left = l; /* l: LH */
RCU_INIT_POINTER(node->avl_right, rl); /* rl: LH or LH+1 */
RCU_INIT_POINTER(node->avl_left, l); /* l: LH */
node->avl_height = rlh + 1; /* LH+1 or LH+2 */
r->avl_right = rr; /* rr: LH+1 */
r->avl_left = node; /* node: LH+1 or LH+2 */
RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH+1 */
RCU_INIT_POINTER(r->avl_left, node); /* node: LH+1 or LH+2 */
r->avl_height = node->avl_height + 1;
*nodep = r;
RCU_INIT_POINTER(*nodep, r);
} else { /* rr: RH, rl: RH+1 */
rlr = rl->avl_right; /* rlr: LH or LH-1 */
rll = rl->avl_left; /* rll: LH or LH-1 */
node->avl_right = rll; /* rll: LH or LH-1 */
node->avl_left = l; /* l: LH */
rlr = rcu_dereference_protected(rl->avl_right,
lockdep_is_held(&peers.lock)); /* rlr: LH or LH-1 */
rll = rcu_dereference_protected(rl->avl_left,
lockdep_is_held(&peers.lock)); /* rll: LH or LH-1 */
RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */
RCU_INIT_POINTER(node->avl_left, l); /* l: LH */
node->avl_height = lh + 1; /* node: LH+1 */
r->avl_right = rr; /* rr: LH */
r->avl_left = rlr; /* rlr: LH or LH-1 */
RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH */
RCU_INIT_POINTER(r->avl_left, rlr); /* rlr: LH or LH-1 */
r->avl_height = lh + 1; /* r: LH+1 */
rl->avl_right = r; /* r: LH+1 */
rl->avl_left = node; /* node: LH+1 */
RCU_INIT_POINTER(rl->avl_right, r); /* r: LH+1 */
RCU_INIT_POINTER(rl->avl_left, node); /* node: LH+1 */
rl->avl_height = lh + 2;
*nodep = rl;
RCU_INIT_POINTER(*nodep, rl);
}
} else {
node->avl_height = (lh > rh ? lh : rh) + 1;
Expand All @@ -303,10 +324,10 @@ static void peer_avl_rebalance(struct inet_peer **stack[],
#define link_to_pool(n) \
do { \
n->avl_height = 1; \
n->avl_left = peer_avl_empty; \
n->avl_right = peer_avl_empty; \
smp_wmb(); /* lockless readers can catch us now */ \
**--stackptr = n; \
n->avl_left = peer_avl_empty_rcu; \
n->avl_right = peer_avl_empty_rcu; \
/* lockless readers can catch us now */ \
rcu_assign_pointer(**--stackptr, n); \
peer_avl_rebalance(stack, stackptr); \
} while (0)

Expand All @@ -330,24 +351,25 @@ static void unlink_from_pool(struct inet_peer *p)
* We use refcnt=-1 to alert lockless readers this entry is deleted.
*/
if (atomic_cmpxchg(&p->refcnt, 1, -1) == 1) {
struct inet_peer **stack[PEER_MAXDEPTH];
struct inet_peer ***stackptr, ***delp;
struct inet_peer __rcu **stack[PEER_MAXDEPTH];
struct inet_peer __rcu ***stackptr, ***delp;
if (lookup(p->v4daddr, stack) != p)
BUG();
delp = stackptr - 1; /* *delp[0] == p */
if (p->avl_left == peer_avl_empty) {
if (p->avl_left == peer_avl_empty_rcu) {
*delp[0] = p->avl_right;
--stackptr;
} else {
/* look for a node to insert instead of p */
struct inet_peer *t;
t = lookup_rightempty(p);
BUG_ON(*stackptr[-1] != t);
BUG_ON(rcu_dereference_protected(*stackptr[-1],
lockdep_is_held(&peers.lock)) != t);
**--stackptr = t->avl_left;
/* t is removed, t->v4daddr > x->v4daddr for any
* x in p->avl_left subtree.
* Put t in the old place of p. */
*delp[0] = t;
RCU_INIT_POINTER(*delp[0], t);
t->avl_left = p->avl_left;
t->avl_right = p->avl_right;
t->avl_height = p->avl_height;
Expand Down Expand Up @@ -414,7 +436,7 @@ static int cleanup_once(unsigned long ttl)
struct inet_peer *inet_getpeer(__be32 daddr, int create)
{
struct inet_peer *p;
struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr;
struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;

/* Look up for the address quickly, lockless.
* Because of a concurrent writer, we might not find an existing entry.
Expand Down

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