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authorPablo Neira Ayuso <pablo@netfilter.org>2021-07-17 11:20:08 +0300
committerPablo Neira Ayuso <pablo@netfilter.org>2021-07-23 15:18:02 +0300
commit32953df7a6eb56bd9b8f18a13034d55f9fc96cfa (patch)
tree48e2e8efcadc59cd46cd93bb7ee0e8994804cb9e /net
parent32c3973d808301e7a980f80fee8818fdf7c82b09 (diff)
downloadlinux-32953df7a6eb56bd9b8f18a13034d55f9fc96cfa.tar.xz
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: 836382dc2471 ("netfilter: nf_tables: add last expression") Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Diffstat (limited to 'net')
-rw-r--r--net/netfilter/nft_last.c20
1 files changed, 13 insertions, 7 deletions
diff --git a/net/netfilter/nft_last.c b/net/netfilter/nft_last.c
index 8088b99f2ee3..304e33cbed9b 100644
--- a/net/netfilter/nft_last.c
+++ b/net/netfilter/nft_last.c
@@ -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;