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ipv4: Restore old dst_free() behavior.

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commit 404e0a8b6a (net: ipv4: fix RCU races on dst refcounts) tried
to solve a race but added a problem at device/fib dismantle time :

We really want to call dst_free() as soon as possible, even if sockets
still have dst in their cache.
dst_release() calls in free_fib_info_rcu() are not welcomed.

Root of the problem was that now we also cache output routes (in
nh_rth_output), we must use call_rcu() instead of call_rcu_bh() in
rt_free(), because output route lookups are done in process context.

Based on feedback and initial patch from David Miller (adding another
call_rcu_bh() call in fib, but it appears it was not the right fix)

I left the inet_sk_rx_dst_set() helper and added __rcu attributes
to nh_rth_output and nh_rth_input to better document what is going on in
this code.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2012-07-31 01:08:23 +00:00 • committed by David S. Miller
parent 5a0d513b62
commit 54764bb647
7 changed files with 50 additions and 50 deletions
Download patch file Download diff file Expand all files Collapse all files

26
net/ipv4/route.c
View file

@ -1199,23 +1199,31 @@ restart:
fnhe->fnhe_stamp = jiffies;
}
static inline void rt_free(struct rtable *rt)
{
call_rcu(&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;
struct rtable *orig, *prev, **p = (struct rtable **)&nh->nh_rth_output;
if (rt_is_input_route(rt))
p = &nh->nh_rth_input;
p = (struct rtable **)&nh->nh_rth_input;
orig = *p;
rt->dst.flags |= DST_RCU_FREE;
dst_hold(&rt->dst);
prev = cmpxchg(p, orig, rt);
if (prev == orig) {
if (orig)
dst_release(&orig->dst);
rt_free(orig);
} else {
dst_release(&rt->dst);
/* 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;
}
}
@ -1412,7 +1420,7 @@ static int __mkroute_input(struct sk_buff *skb,
do_cache = false;
if (res->fi) {
if (!itag) {
rth = FIB_RES_NH(*res).nh_rth_input;
rth = rcu_dereference(FIB_RES_NH(*res).nh_rth_input);
if (rt_cache_valid(rth)) {
skb_dst_set_noref(skb, &rth->dst);
goto out;
@ -1574,7 +1582,7 @@ local_input:
do_cache = false;
if (res.fi) {
if (!itag) {
rth = FIB_RES_NH(res).nh_rth_input;
rth = rcu_dereference(FIB_RES_NH(res).nh_rth_input);
if (rt_cache_valid(rth)) {
skb_dst_set_noref(skb, &rth->dst);
err = 0;
@ -1742,7 +1750,7 @@ static struct rtable *__mkroute_output(const struct fib_result *res,
if (fi) {
fnhe = find_exception(&FIB_RES_NH(*res), fl4->daddr);
if (!fnhe) {
rth = FIB_RES_NH(*res).nh_rth_output;
rth = rcu_dereference(FIB_RES_NH(*res).nh_rth_output);
if (rt_cache_valid(rth)) {
dst_hold(&rth->dst);
return rth;