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xfrm: state: add sequence count to detect hash resizes

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Once xfrm_state_find is lockless we have to cope with a concurrent
resize opertion.

We use a sequence counter to block in case a resize is in progress
and to detect if we might have missed a state that got moved to
a new 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 2016-08-09 12:16:07 +02:00 committed by Steffen Klassert
parent df7274eb70
commit b65e3d7be0
1 changed files with 15 additions and 0 deletions
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15
net/xfrm/xfrm_state.c
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@ -36,6 +36,7 @@
*/
static unsigned int xfrm_state_hashmax __read_mostly = 1 * 1024 * 1024;
static __read_mostly seqcount_t xfrm_state_hash_generation = SEQCNT_ZERO(xfrm_state_hash_generation);
static inline bool xfrm_state_hold_rcu(struct xfrm_state __rcu *x)
{
@ -127,6 +128,7 @@ static void xfrm_hash_resize(struct work_struct *work)
}
spin_lock_bh(&net->xfrm.xfrm_state_lock);
write_seqcount_begin(&xfrm_state_hash_generation);
nhashmask = (nsize / sizeof(struct hlist_head)) - 1U;
for (i = net->xfrm.state_hmask; i >= 0; i--)
@ -143,6 +145,7 @@ static void xfrm_hash_resize(struct work_struct *work)
net->xfrm.state_byspi = nspi;
net->xfrm.state_hmask = nhashmask;
write_seqcount_end(&xfrm_state_hash_generation);
spin_unlock_bh(&net->xfrm.xfrm_state_lock);
osize = (ohashmask + 1) * sizeof(struct hlist_head);
@ -787,10 +790,13 @@ xfrm_state_find(const xfrm_address_t *daddr, const xfrm_address_t *saddr,
struct xfrm_state *best = NULL;
u32 mark = pol->mark.v & pol->mark.m;
unsigned short encap_family = tmpl->encap_family;
unsigned int sequence;
struct km_event c;
to_put = NULL;
sequence = read_seqcount_begin(&xfrm_state_hash_generation);
spin_lock_bh(&net->xfrm.xfrm_state_lock);
h = xfrm_dst_hash(net, daddr, saddr, tmpl->reqid, encap_family);
hlist_for_each_entry_rcu(x, net->xfrm.state_bydst + h, bydst) {
@ -894,6 +900,15 @@ out:
spin_unlock_bh(&net->xfrm.xfrm_state_lock);
if (to_put)
xfrm_state_put(to_put);
if (read_seqcount_retry(&xfrm_state_hash_generation, sequence)) {
*err = -EAGAIN;
if (x) {
xfrm_state_put(x);
x = NULL;
}
}
return x;
}