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Commit 0830106c authored by Wei Wang's avatar Wei Wang Committed by David S. Miller
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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: default avatarWei Wang <weiwan@google.com>
Acked-by: default avatarMartin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4a6ce2b6

net/ipv4/fib_semantics.c

+4 −1
Original line number Diff line number Diff line
@@ -152,6 +152,7 @@ static void rt_fibinfo_free(struct rtable __rcu **rtp) 
	 * free_fib_info_rcu()

	 */



	dst_release(&rt->dst);

	dst_free(&rt->dst);

}
@@ -194,9 +195,11 @@ static void rt_fibinfo_free_cpus(struct rtable __rcu * __percpu *rtp) 
		struct rtable *rt;



		rt = rcu_dereference_protected(*per_cpu_ptr(rtp, cpu), 1);

		if (rt)

		if (rt) {

			dst_release(&rt->dst);

			dst_free(&rt->dst);

		}

	}

	free_percpu(rtp);

}

net/ipv4/route.c

+16 −3
Original line number Diff line number Diff line
@@ -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;

}