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Commit e1e551bc authored by Florian Westphal's avatar Florian Westphal Committed by Steffen Klassert
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xfrm: policy: prepare policy_bydst hash for rcu lookups 



Since commit 56f04730
("xfrm: add rcu grace period in xfrm_policy_destroy()") xfrm policy
objects are already free'd via rcu.

In order to make more places lockless (i.e. use rcu_read_lock instead of
grabbing read-side of policy rwlock) we only need to:

- use rcu_assign_pointer to store address of new hash table backend memory
- add rcu barrier so that freeing of old memory is delayed (expansion
  and free happens from system workqueue, so synchronize_rcu is fine)
- use rcu_dereference to fetch current address of the hash table.

Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
Signed-off-by: default avatarSteffen Klassert <steffen.klassert@secunet.com>
parent a5eefc1d

net/xfrm/xfrm_policy.c

+14 −6
Original line number Diff line number Diff line
@@ -385,9 +385,11 @@ static struct hlist_head *policy_hash_bysel(struct net *net, 
	__get_hash_thresh(net, family, dir, &dbits, &sbits);

	hash = __sel_hash(sel, family, hmask, dbits, sbits);



	return (hash == hmask + 1 ?

		&net->xfrm.policy_inexact[dir] :

		net->xfrm.policy_bydst[dir].table + hash);

	if (hash == hmask + 1)

		return &net->xfrm.policy_inexact[dir];



	return rcu_dereference_check(net->xfrm.policy_bydst[dir].table,

		     lockdep_is_held(&net->xfrm.xfrm_policy_lock)) + hash;

}



static struct hlist_head *policy_hash_direct(struct net *net,
@@ -403,7 +405,8 @@ static struct hlist_head *policy_hash_direct(struct net *net, 
	__get_hash_thresh(net, family, dir, &dbits, &sbits);

	hash = __addr_hash(daddr, saddr, family, hmask, dbits, sbits);



	return net->xfrm.policy_bydst[dir].table + hash;

	return rcu_dereference_check(net->xfrm.policy_bydst[dir].table,

		     lockdep_is_held(&net->xfrm.xfrm_policy_lock)) + hash;

}



static void xfrm_dst_hash_transfer(struct net *net,
@@ -468,8 +471,8 @@ static void xfrm_bydst_resize(struct net *net, int dir) 
	unsigned int hmask = net->xfrm.policy_bydst[dir].hmask;

	unsigned int nhashmask = xfrm_new_hash_mask(hmask);

	unsigned int nsize = (nhashmask + 1) * sizeof(struct hlist_head);

	struct hlist_head *odst = net->xfrm.policy_bydst[dir].table;

	struct hlist_head *ndst = xfrm_hash_alloc(nsize);

	struct hlist_head *odst;

	int i;



	if (!ndst)
@@ -477,14 +480,19 @@ static void xfrm_bydst_resize(struct net *net, int dir) 


	write_lock_bh(&net->xfrm.xfrm_policy_lock);



	odst = rcu_dereference_protected(net->xfrm.policy_bydst[dir].table,

				lockdep_is_held(&net->xfrm.xfrm_policy_lock));



	for (i = hmask; i >= 0; i--)

		xfrm_dst_hash_transfer(net, odst + i, ndst, nhashmask, dir);



	net->xfrm.policy_bydst[dir].table = ndst;

	rcu_assign_pointer(net->xfrm.policy_bydst[dir].table, ndst);

	net->xfrm.policy_bydst[dir].hmask = nhashmask;



	write_unlock_bh(&net->xfrm.xfrm_policy_lock);



	synchronize_rcu();



	xfrm_hash_free(odst, (hmask + 1) * sizeof(struct hlist_head));

}