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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: Wei Wang <weiwan@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Wei Wang 2017-06-17 10:42:29 -07:00 committed by David S. Miller
parent 4a6ce2b6f2
commit 0830106c53
2 changed files with 20 additions and 4 deletions
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5
net/ipv4/fib_semantics.c
View File

@ -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);
}
@ -194,8 +195,10 @@ 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);
}

19
net/ipv4/route.c
View File

@ -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;
}