Previously, deleting peers would require traversing the entire trie in order to rebalance nodes and safely free them. This meant that removing 1000 peers from a trie with a half million nodes would take an extremely long time, during which we're holding the rtnl lock. Large-scale users were reporting 200ms latencies added to the networking stack as a whole every time their userspace software would queue up significant removals. That's a serious situation.
This commit fixes that by maintaining a double pointer to the parent's bit pointer for each node, and then using the already existing node list belonging to each peer to go directly to the node, fix up its pointers, and free it with RCU. This means removal is O(1) instead of O(n), and we don't use gobs of stack.
The removal algorithm has the same downside as the code that it fixes: it won't collapse needlessly long runs of fillers. We can enhance that in the future if it ever becomes a problem. This commit documents that limitation with a TODO comment in code, a small but meaningful improvement over the prior situation.
Currently the biggest flaw, which the next commit addresses, is that because this increases the node size on 64-bit machines from 60 bytes to 68 bytes. 60 rounds up to 64, but 68 rounds up to 128. So we wind up using twice as much memory per node, because of power-of-two allocations, which is a big bummer. We'll need to figure something out there.
Fixes: e7096c131e51 ("net: WireGuard secure network tunnel") Cc: stable@vger.kernel.org Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com --- drivers/net/wireguard/allowedips.c | 132 ++++++++++++----------------- drivers/net/wireguard/allowedips.h | 9 +- 2 files changed, 57 insertions(+), 84 deletions(-)
diff --git a/drivers/net/wireguard/allowedips.c b/drivers/net/wireguard/allowedips.c index 3725e9cd85f4..2785cfd3a221 100644 --- a/drivers/net/wireguard/allowedips.c +++ b/drivers/net/wireguard/allowedips.c @@ -66,60 +66,6 @@ static void root_remove_peer_lists(struct allowedips_node *root) } }
-static void walk_remove_by_peer(struct allowedips_node __rcu **top, - struct wg_peer *peer, struct mutex *lock) -{ -#define REF(p) rcu_access_pointer(p) -#define DEREF(p) rcu_dereference_protected(*(p), lockdep_is_held(lock)) -#define PUSH(p) ({ \ - WARN_ON(IS_ENABLED(DEBUG) && len >= 128); \ - stack[len++] = p; \ - }) - - struct allowedips_node __rcu **stack[128], **nptr; - struct allowedips_node *node, *prev; - unsigned int len; - - if (unlikely(!peer || !REF(*top))) - return; - - for (prev = NULL, len = 0, PUSH(top); len > 0; prev = node) { - nptr = stack[len - 1]; - node = DEREF(nptr); - if (!node) { - --len; - continue; - } - if (!prev || REF(prev->bit[0]) == node || - REF(prev->bit[1]) == node) { - if (REF(node->bit[0])) - PUSH(&node->bit[0]); - else if (REF(node->bit[1])) - PUSH(&node->bit[1]); - } else if (REF(node->bit[0]) == prev) { - if (REF(node->bit[1])) - PUSH(&node->bit[1]); - } else { - if (rcu_dereference_protected(node->peer, - lockdep_is_held(lock)) == peer) { - RCU_INIT_POINTER(node->peer, NULL); - list_del_init(&node->peer_list); - if (!node->bit[0] || !node->bit[1]) { - rcu_assign_pointer(*nptr, DEREF( - &node->bit[!REF(node->bit[0])])); - kfree_rcu(node, rcu); - node = DEREF(nptr); - } - } - --len; - } - } - -#undef REF -#undef DEREF -#undef PUSH -} - static unsigned int fls128(u64 a, u64 b) { return a ? fls64(a) + 64U : fls64(b); @@ -224,6 +170,7 @@ static int add(struct allowedips_node __rcu **trie, u8 bits, const u8 *key, RCU_INIT_POINTER(node->peer, peer); list_add_tail(&node->peer_list, &peer->allowedips_list); copy_and_assign_cidr(node, key, cidr, bits); + rcu_assign_pointer(node->parent_bit, trie); rcu_assign_pointer(*trie, node); return 0; } @@ -243,9 +190,9 @@ static int add(struct allowedips_node __rcu **trie, u8 bits, const u8 *key, if (!node) { down = rcu_dereference_protected(*trie, lockdep_is_held(lock)); } else { - down = rcu_dereference_protected(CHOOSE_NODE(node, key), - lockdep_is_held(lock)); + down = rcu_dereference_protected(CHOOSE_NODE(node, key), lockdep_is_held(lock)); if (!down) { + rcu_assign_pointer(newnode->parent_bit, &CHOOSE_NODE(node, key)); rcu_assign_pointer(CHOOSE_NODE(node, key), newnode); return 0; } @@ -254,29 +201,37 @@ static int add(struct allowedips_node __rcu **trie, u8 bits, const u8 *key, parent = node;
if (newnode->cidr == cidr) { + rcu_assign_pointer(down->parent_bit, &CHOOSE_NODE(newnode, down->bits)); rcu_assign_pointer(CHOOSE_NODE(newnode, down->bits), down); - if (!parent) + if (!parent) { + rcu_assign_pointer(newnode->parent_bit, trie); rcu_assign_pointer(*trie, newnode); - else - rcu_assign_pointer(CHOOSE_NODE(parent, newnode->bits), - newnode); - } else { - node = kzalloc(sizeof(*node), GFP_KERNEL); - if (unlikely(!node)) { - list_del(&newnode->peer_list); - kfree(newnode); - return -ENOMEM; + } else { + rcu_assign_pointer(newnode->parent_bit, &CHOOSE_NODE(parent, newnode->bits)); + rcu_assign_pointer(CHOOSE_NODE(parent, newnode->bits), newnode); } - INIT_LIST_HEAD(&node->peer_list); - copy_and_assign_cidr(node, newnode->bits, cidr, bits); - - rcu_assign_pointer(CHOOSE_NODE(node, down->bits), down); - rcu_assign_pointer(CHOOSE_NODE(node, newnode->bits), newnode); - if (!parent) - rcu_assign_pointer(*trie, node); - else - rcu_assign_pointer(CHOOSE_NODE(parent, node->bits), - node); + return 0; + } + + node = kzalloc(sizeof(*node), GFP_KERNEL); + if (unlikely(!node)) { + list_del(&newnode->peer_list); + kfree(newnode); + return -ENOMEM; + } + INIT_LIST_HEAD(&node->peer_list); + copy_and_assign_cidr(node, newnode->bits, cidr, bits); + + rcu_assign_pointer(down->parent_bit, &CHOOSE_NODE(node, down->bits)); + rcu_assign_pointer(CHOOSE_NODE(node, down->bits), down); + rcu_assign_pointer(newnode->parent_bit, &CHOOSE_NODE(node, newnode->bits)); + rcu_assign_pointer(CHOOSE_NODE(node, newnode->bits), newnode); + if (!parent) { + rcu_assign_pointer(node->parent_bit, trie); + rcu_assign_pointer(*trie, node); + } else { + rcu_assign_pointer(node->parent_bit, &CHOOSE_NODE(parent, node->bits)); + rcu_assign_pointer(CHOOSE_NODE(parent, node->bits), node); } return 0; } @@ -335,9 +290,30 @@ int wg_allowedips_insert_v6(struct allowedips *table, const struct in6_addr *ip, void wg_allowedips_remove_by_peer(struct allowedips *table, struct wg_peer *peer, struct mutex *lock) { + struct allowedips_node *node, *child, *tmp; + + if (list_empty(&peer->allowedips_list)) + return; ++table->seq; - walk_remove_by_peer(&table->root4, peer, lock); - walk_remove_by_peer(&table->root6, peer, lock); + list_for_each_entry_safe(node, tmp, &peer->allowedips_list, peer_list) { + list_del_init(&node->peer_list); + RCU_INIT_POINTER(node->peer, NULL); + if (node->bit[0] && node->bit[1]) + continue; + child = rcu_dereference_protected( + node->bit[!rcu_access_pointer(node->bit[0])], + lockdep_is_held(lock)); + if (child) + child->parent_bit = node->parent_bit; + *rcu_dereference_protected(node->parent_bit, lockdep_is_held(lock)) = child; + kfree_rcu(node, rcu); + + /* TODO: Note that we currently don't walk up and down in order to + * free any potential filler nodes. This means that this function + * doesn't free up as much as it could, which could be revisited + * at some point. + */ + } }
int wg_allowedips_read_node(struct allowedips_node *node, u8 ip[16], u8 *cidr) diff --git a/drivers/net/wireguard/allowedips.h b/drivers/net/wireguard/allowedips.h index e5c83cafcef4..f08f552e6852 100644 --- a/drivers/net/wireguard/allowedips.h +++ b/drivers/net/wireguard/allowedips.h @@ -15,14 +15,11 @@ struct wg_peer; struct allowedips_node { struct wg_peer __rcu *peer; struct allowedips_node __rcu *bit[2]; - /* While it may seem scandalous that we waste space for v4, - * we're alloc'ing to the nearest power of 2 anyway, so this - * doesn't actually make a difference. - */ - u8 bits[16] __aligned(__alignof(u64)); u8 cidr, bit_at_a, bit_at_b, bitlen; + u8 bits[16] __aligned(__alignof(u64));
- /* Keep rarely used list at bottom to be beyond cache line. */ + /* Keep rarely used members at bottom to be beyond cache line. */ + struct allowedips_node *__rcu *parent_bit; /* XXX: this puts us at 68->128 bytes instead of 60->64 bytes!! */ union { struct list_head peer_list; struct rcu_head rcu;