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netfilter: nft_last: avoid possible false sharing

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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: 836382dc24 ("netfilter: nf_tables: add last expression")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Pablo Neira Ayuso 2021-07-17 10:20:08 +02:00
parent 32c3973d80
commit 32953df7a6
1 changed files with 13 additions and 7 deletions
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20
net/netfilter/nft_last.c
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@ -48,24 +48,30 @@ static void nft_last_eval(const struct nft_expr *expr,
{ {
struct nft_last_priv *priv = nft_expr_priv(expr); struct nft_last_priv *priv = nft_expr_priv(expr);
priv->last_jiffies = jiffies; if (READ_ONCE(priv->last_jiffies) != jiffies)
priv->last_set = 1; 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) static int nft_last_dump(struct sk_buff *skb, const struct nft_expr *expr)
{ {
struct nft_last_priv *priv = nft_expr_priv(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; __be64 msecs;
if (time_before(jiffies, priv->last_jiffies)) if (time_before(jiffies, last_jiffies)) {
priv->last_set = 0; WRITE_ONCE(priv->last_set, 0);
last_set = 0;
}
if (priv->last_set) if (last_set)
msecs = nf_jiffies64_to_msecs(jiffies - priv->last_jiffies); msecs = nf_jiffies64_to_msecs(jiffies - last_jiffies);
else else
msecs = 0; 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)) nla_put_be64(skb, NFTA_LAST_MSECS, msecs, NFTA_LAST_PAD))
goto nla_put_failure; goto nla_put_failure;