Commit 32953df7 authored by Pablo Neira Ayuso's avatar Pablo Neira Ayuso
Browse files

netfilter: nft_last: avoid possible false sharing 

Use the idiom described in:

https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE#it-may-improve-performance



Moreover, prevent a compiler optimization.

Fixes: 836382dc ("netfilter: nf_tables: add last expression")
Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
parent 32c3973d

net/netfilter/nft_last.c

+13 −7
Original line number Diff line number Diff line
@@ -48,24 +48,30 @@ static void nft_last_eval(const struct nft_expr *expr, 
{

	struct nft_last_priv *priv = nft_expr_priv(expr);



	priv->last_jiffies = jiffies;

	priv->last_set = 1;

	if (READ_ONCE(priv->last_jiffies) != jiffies)

		WRITE_ONCE(priv->last_jiffies, jiffies);

	if (READ_ONCE(priv->last_set) == 0)

		WRITE_ONCE(priv->last_set, 1);

}



static int nft_last_dump(struct sk_buff *skb, const struct nft_expr *expr)

{

	struct nft_last_priv *priv = nft_expr_priv(expr);

	unsigned long last_jiffies = READ_ONCE(priv->last_jiffies);

	u32 last_set = READ_ONCE(priv->last_set);

	__be64 msecs;



	if (time_before(jiffies, priv->last_jiffies))

		priv->last_set = 0;

	if (time_before(jiffies, last_jiffies)) {

		WRITE_ONCE(priv->last_set, 0);

		last_set = 0;

	}



	if (priv->last_set)

		msecs = nf_jiffies64_to_msecs(jiffies - priv->last_jiffies);

	if (last_set)

		msecs = nf_jiffies64_to_msecs(jiffies - last_jiffies);

	else

		msecs = 0;



	if (nla_put_be32(skb, NFTA_LAST_SET, htonl(priv->last_set)) ||

	if (nla_put_be32(skb, NFTA_LAST_SET, htonl(last_set)) ||

	    nla_put_be64(skb, NFTA_LAST_MSECS, msecs, NFTA_LAST_PAD))

		goto nla_put_failure;