inetpeer: __rcu annotations

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>

2 files changed, 81 insertions, 59 deletions

diff --git a/include/net/inetpeer.h b/include/net/inetpeer.h
index 417d0c894f29..fe239bfe5f7f 100644
--- a/include/net/inetpeer.h
+++ b/include/net/inetpeer.h
@@ -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;
diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
index 9ffa24b9a804..9e94d7cf4f8a 100644
--- a/net/ipv4/inetpeer.c
+++ b/net/ipv4/inetpeer.c
@@ -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,
 };
@@ -156,11 +157,14 @@ 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)  \
@@ -168,7 +172,8 @@ static void unlink_from_unused(struct inet_peer *p)
                 else                                            \
                         v = &u->avl_right;                      \
                 *stackptr++ = v;                                \
-                u = *v;                                         \
+                u = rcu_dereference_protected(*v,               \
+                        lockdep_is_held(&peers.lock));          \
         }                                                       \
         u;                                                      \
 })
@@ -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;                                                      \
 })
@@ -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;
@@ -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)
 
@@ -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;
@@ -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.