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>

diff --git a/include/net/inetpeer.h b/include/net/inetpeer.h
index 417d0c8..fe239bf 100644 (file)
--- 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 9ffa24b..9e94d7c 100644 (file)
--- 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.