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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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4
net/ipv4/fib_semantics.c
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@@ -172,9 +172,9 @@ static void free_fib_info_rcu(struct rcu_head *head)
if (nexthop_nh->nh_exceptions)
free_nh_exceptions(nexthop_nh);
if (nexthop_nh->nh_rth_output)
dst_free(&nexthop_nh->nh_rth_output->dst);
dst_release(&nexthop_nh->nh_rth_output->dst);
if (nexthop_nh->nh_rth_input)
dst_free(&nexthop_nh->nh_rth_input->dst);
dst_release(&nexthop_nh->nh_rth_input->dst);
} endfor_nexthops(fi);
release_net(fi->fib_net);