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tc/act: remove unneeded RCU lock in action callback

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Each lockless action currently does its own RCU locking in ->act().
This allows using plain RCU accessor, even if the context
is really RCU BH.

This change drops the per action RCU lock, replace the accessors
with the _bh variant, cleans up a bit the surrounding code and
documents the RCU status in the relevant header.
No functional nor performance change is intended.

The goal of this patch is clarifying that the RCU critical section
used by the tc actions extends up to the classifier's caller.

v1 -> v2:
 - preserve rcu lock in act_bpf: it's needed by eBPF helpers,
   as pointed out by Daniel

v3 -> v4:
 - fixed some typos in the commit message (JiriP)

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paolo Abeni
2018-07-30 14:30:43 +02:00
committed by David S. Miller
parent 802bfb1915
commit 7fd4b288ea
10 changed files with 29 additions and 56 deletions
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21
net/sched/act_skbmod.c
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@@ -41,20 +41,14 @@ static int tcf_skbmod_run(struct sk_buff *skb, const struct tc_action *a,
* then MAX_EDIT_LEN needs to change appropriately
*/
err = skb_ensure_writable(skb, MAX_EDIT_LEN);
if (unlikely(err)) { /* best policy is to drop on the floor */
qstats_overlimit_inc(this_cpu_ptr(d->common.cpu_qstats));
return TC_ACT_SHOT;
}
if (unlikely(err)) /* best policy is to drop on the floor */
goto drop;
rcu_read_lock();
action = READ_ONCE(d->tcf_action);
if (unlikely(action == TC_ACT_SHOT)) {
qstats_overlimit_inc(this_cpu_ptr(d->common.cpu_qstats));
rcu_read_unlock();
return action;
}
if (unlikely(action == TC_ACT_SHOT))
goto drop;
p = rcu_dereference(d->skbmod_p);
p = rcu_dereference_bh(d->skbmod_p);
flags = p->flags;
if (flags & SKBMOD_F_DMAC)
ether_addr_copy(eth_hdr(skb)->h_dest, p->eth_dst);
@@ -62,7 +56,6 @@ static int tcf_skbmod_run(struct sk_buff *skb, const struct tc_action *a,
ether_addr_copy(eth_hdr(skb)->h_source, p->eth_src);
if (flags & SKBMOD_F_ETYPE)
eth_hdr(skb)->h_proto = p->eth_type;
rcu_read_unlock();
if (flags & SKBMOD_F_SWAPMAC) {
u16 tmpaddr[ETH_ALEN / 2]; /* ether_addr_copy() requirement */
@@ -73,6 +66,10 @@ static int tcf_skbmod_run(struct sk_buff *skb, const struct tc_action *a,
}
return action;
drop:
qstats_overlimit_inc(this_cpu_ptr(d->common.cpu_qstats));
return TC_ACT_SHOT;
}
static const struct nla_policy skbmod_policy[TCA_SKBMOD_MAX + 1] = {