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xfrm: policy: prepare policy_bydst hash for rcu lookups 

Since commit 56f047305d
("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: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
This commit is contained in:
Florian Westphal 2016-08-11 15:17:53 +02:00 committed by Steffen Klassert
parent a5eefc1df6
commit e1e551bc56
1 changed files with 14 additions and 6 deletions
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20
net/xfrm/xfrm_policy.c
View File

@ -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));
}