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Message-ID: <20141021133144.GA8802@casper.infradead.org>
Date: Tue, 21 Oct 2014 14:31:44 +0100
From: Thomas Graf <tgraf@...g.ch>
To: "Steinar H. Gunderson" <sgunderson@...foot.com>
Cc: linux-kernel@...r.kernel.org,
"David S. Miller" <davem@...emloft.net>,
Nikolay Aleksandrov <nikolay@...hat.com>
Subject: Re: getaddrinfo slowdown in 3.17.1, due to getifaddrs
On 10/21/14 at 03:25pm, Steinar H. Gunderson wrote:
> On Fri, Oct 17, 2014 at 07:25:17AM +0100, Thomas Graf wrote:
> > I think the only option at this point is to re-add the nltable lock to
> > netlink_lookup() so we can drop the synchronize_net() until we find a
> > way to RCUify socket destruction. I will cook up a patch today unless
> > somebody can come up with a smarter way to work around needing the
> > synchronize_net().
>
> Did you end up with a patch? We'd like to reboot the server in question
> soon-ish, but it's an open question whether we should go to 3.16.x, revert
> exactly the patches in question or something else.
I'm currently testing the patch below and will submit with proper
tested by attributions later today.
>From 3605e498c0b025054d17cc2943cae70d3df2a427 Mon Sep 17 00:00:00 2001
Message-Id: <3605e498c0b025054d17cc2943cae70d3df2a427.1413834710.git.tgraf@...g.ch>
From: Thomas Graf <tgraf@...g.ch>
Date: Fri, 17 Oct 2014 11:33:44 +0200
Subject: [PATCH] netlink: Re-add locking to netlink_lookup() and seq walker
The synchronize_rcu() in netlink_release() introduces unacceptable
latency. Reintroduce minimal lookup so we can drop the
synchronize_rcu() until socket destruction has been RCUfied.
Signed-off-by: Thomas Graf <tgraf@...g.ch>
---
net/netlink/af_netlink.c | 37 +++++++++++++++++++++++++------------
1 file changed, 25 insertions(+), 12 deletions(-)
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 7a186e7..f1de72d 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -96,6 +96,14 @@ static DECLARE_WAIT_QUEUE_HEAD(nl_table_wait);
static int netlink_dump(struct sock *sk);
static void netlink_skb_destructor(struct sk_buff *skb);
+/* nl_table locking explained:
+ * Lookup and traversal are protected with nl_sk_hash_lock or nl_table_lock
+ * combined with an RCU read-side lock. Insertion and removal are protected
+ * with nl_sk_hash_lock while using RCU list modification primitives and may
+ * run in parallel to nl_table_lock protected lookups. Destruction of the
+ * Netlink socket may only occur *after* nl_table_lock has been acquired
+ * either during or after the socket has been removed from the list.
+ */
DEFINE_RWLOCK(nl_table_lock);
EXPORT_SYMBOL_GPL(nl_table_lock);
static atomic_t nl_table_users = ATOMIC_INIT(0);
@@ -109,10 +117,10 @@ EXPORT_SYMBOL_GPL(nl_sk_hash_lock);
static int lockdep_nl_sk_hash_is_held(void)
{
#ifdef CONFIG_LOCKDEP
- return (debug_locks) ? lockdep_is_held(&nl_sk_hash_lock) : 1;
-#else
- return 1;
+ if (debug_locks)
+ return lockdep_is_held(&nl_sk_hash_lock) || lockdep_is_held(&nl_table_lock);
#endif
+ return 1;
}
static ATOMIC_NOTIFIER_HEAD(netlink_chain);
@@ -1028,11 +1036,13 @@ static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
struct netlink_table *table = &nl_table[protocol];
struct sock *sk;
+ read_lock(&nl_table_lock);
rcu_read_lock();
sk = __netlink_lookup(table, portid, net);
if (sk)
sock_hold(sk);
rcu_read_unlock();
+ read_unlock(&nl_table_lock);
return sk;
}
@@ -1257,9 +1267,6 @@ static int netlink_release(struct socket *sock)
}
netlink_table_ungrab();
- /* Wait for readers to complete */
- synchronize_net();
-
kfree(nlk->groups);
nlk->groups = NULL;
@@ -1281,6 +1288,7 @@ static int netlink_autobind(struct socket *sock)
retry:
cond_resched();
+ netlink_table_grab();
rcu_read_lock();
if (__netlink_lookup(table, portid, net)) {
/* Bind collision, search negative portid values. */
@@ -1288,9 +1296,11 @@ retry:
if (rover > -4097)
rover = -4097;
rcu_read_unlock();
+ netlink_table_ungrab();
goto retry;
}
rcu_read_unlock();
+ netlink_table_ungrab();
err = netlink_insert(sk, net, portid);
if (err == -EADDRINUSE)
@@ -2921,14 +2931,16 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
}
static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
- __acquires(RCU)
+ __acquires(nl_table_lock) __acquires(RCU)
{
+ read_lock(&nl_table_lock);
rcu_read_lock();
return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
}
static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
+ struct rhashtable *ht;
struct netlink_sock *nlk;
struct nl_seq_iter *iter;
struct net *net;
@@ -2943,19 +2955,19 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
iter = seq->private;
nlk = v;
- rht_for_each_entry_rcu(nlk, nlk->node.next, node)
+ i = iter->link;
+ ht = &nl_table[i].hash;
+ rht_for_each_entry(nlk, nlk->node.next, ht, node)
if (net_eq(sock_net((struct sock *)nlk), net))
return nlk;
- i = iter->link;
j = iter->hash_idx + 1;
do {
- struct rhashtable *ht = &nl_table[i].hash;
const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
for (; j < tbl->size; j++) {
- rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+ rht_for_each_entry(nlk, tbl->buckets[j], ht, node) {
if (net_eq(sock_net((struct sock *)nlk), net)) {
iter->link = i;
iter->hash_idx = j;
@@ -2971,9 +2983,10 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
}
static void netlink_seq_stop(struct seq_file *seq, void *v)
- __releases(RCU)
+ __releases(RCU) __releases(nl_table_lock)
{
rcu_read_unlock();
+ read_unlock(&nl_table_lock);
}
--
1.9.3
--
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