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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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16
net/ipv4/route.c
View file

@ -1199,11 +1199,6 @@ restart:
fnhe->fnhe_stamp = jiffies;
}
static inline void rt_free(struct rtable *rt)
{
call_rcu_bh(&rt->dst.rcu_head, dst_rcu_free);
}
static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
{
struct rtable *orig, *prev, **p = &nh->nh_rth_output;
@ -1213,17 +1208,14 @@ static void rt_cache_route(struct fib_nh *nh, struct rtable *rt)
orig = *p;
rt->dst.flags |= DST_RCU_FREE;
dst_hold(&rt->dst);
prev = cmpxchg(p, orig, rt);
if (prev == orig) {
if (orig)
rt_free(orig);
dst_release(&orig->dst);
} else {
/* Routes we intend to cache in the FIB nexthop have
* the DST_NOCACHE bit clear. However, if we are
* unsuccessful at storing this route into the cache
* we really need to set it.
*/
rt->dst.flags |= DST_NOCACHE;
dst_release(&rt->dst);
}
}