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net: ipv4: fix RCU races on dst refcounts

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commit c6cffba4ff (ipv4: Fix input route performance regression.)
added various fatal races with dst refcounts.

crashes happen on tcp workloads if routes are added/deleted at the same
time.

The dst_free() calls from free_fib_info_rcu() are clearly racy.

We need instead regular dst refcounting (dst_release()) and make
sure dst_release() is aware of RCU grace periods :

Add DST_RCU_FREE flag so that dst_release() respects an RCU grace period
before dst destruction for cached dst

Introduce a new inet_sk_rx_dst_set() helper, using atomic_inc_not_zero()
to make sure we dont increase a zero refcount (On a dst currently
waiting an rcu grace period before destruction)

rt_cache_route() must take a reference on the new cached route, and
release it if was not able to install it.

With this patch, my machines survive various benchmarks.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2012-07-29 23:20:37 +00:00 • committed by David S. Miller
parent cca32e4bf9
commit 404e0a8b6a
9 changed files with 55 additions and 35 deletions
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3
net/ipv4/tcp_minisocks.c
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@ -387,8 +387,7 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
struct tcp_sock *oldtp = tcp_sk(sk);
struct tcp_cookie_values *oldcvp = oldtp->cookie_values;
newsk->sk_rx_dst = dst_clone(skb_dst(skb));
inet_sk(newsk)->rx_dst_ifindex = skb->skb_iif;
inet_sk_rx_dst_set(newsk, skb);
/* TCP Cookie Transactions require space for the cookie pair,
* as it differs for each connection. There is no need to