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authorWei Wang <weiwan@google.com>2017-06-17 10:42:29 -0700
committerDavid S. Miller <davem@davemloft.net>2017-06-17 22:53:59 -0400
commit0830106c53900181d336350581119af09e123bf3 (patch)
tree23954c6a70cb21f051b24492757c4c2a2daa34ac /net/ipv4/route.c
parent4a6ce2b6f2ecabbddcfe47e7cf61dd0f00b10e36 (diff)
ipv4: take dst->__refcnt when caching dst in fib
In IPv4 routing code, fib_nh and fib_nh_exception can hold pointers to struct rtable but they never increment dst->__refcnt. This leads to the need of the dst garbage collector because when user is done with this dst and calls dst_release(), it can only decrement dst->__refcnt and can not free the dst even it sees dst->__refcnt drops from 1 to 0 (unless DST_NOCACHE flag is set) because the routing code might still hold reference to it. And when the routing code tries to delete a route, it has to put the dst to the gc_list if dst->__refcnt is not yet 0 and have a gc thread running periodically to check on dst->__refcnt and finally to free dst when refcnt becomes 0. This patch increments dst->__refcnt when fib_nh/fib_nh_exception holds reference to this dst and properly release the dst when fib_nh/fib_nh_exception has been updated with a new dst. This patch is a preparation in order to fully get rid of dst gc later. Signed-off-by: Wei Wang <weiwan@google.com> Acked-by: Martin KaFai Lau <kafai@fb.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/route.c')
-rw-r--r--net/ipv4/route.c19
1 files changed, 16 insertions, 3 deletions
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 0a843ef2b709..3dee0043117e 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -603,11 +603,13 @@ static void fnhe_flush_routes(struct fib_nh_exception *fnhe)
rt = rcu_dereference(fnhe->fnhe_rth_input);
if (rt) {
RCU_INIT_POINTER(fnhe->fnhe_rth_input, NULL);
+ dst_release(&rt->dst);
rt_free(rt);
}
rt = rcu_dereference(fnhe->fnhe_rth_output);
if (rt) {
RCU_INIT_POINTER(fnhe->fnhe_rth_output, NULL);
+ dst_release(&rt->dst);
rt_free(rt);
}
}
@@ -1332,9 +1334,12 @@ static bool rt_bind_exception(struct rtable *rt, struct fib_nh_exception *fnhe,
rt->rt_gateway = daddr;
if (!(rt->dst.flags & DST_NOCACHE)) {
+ dst_hold(&rt->dst);
rcu_assign_pointer(*porig, rt);
- if (orig)
+ if (orig) {
+ dst_release(&orig->dst);
rt_free(orig);
+ }
ret = true;
}
@@ -1357,12 +1362,20 @@ static bool rt_cache_route(struct fib_nh *nh, struct rtable *rt)
}
orig = *p;
+ /* hold dst before doing cmpxchg() to avoid race condition
+ * on this dst
+ */
+ dst_hold(&rt->dst);
prev = cmpxchg(p, orig, rt);
if (prev == orig) {
- if (orig)
+ if (orig) {
+ dst_release(&orig->dst);
rt_free(orig);
- } else
+ }
+ } else {
+ dst_release(&rt->dst);
ret = false;
+ }
return ret;
}