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| author | Pablo Neira Ayuso <pablo@netfilter.org> | 2021-07-17 11:20:08 +0300 |
|---|---|---|
| committer | Pablo Neira Ayuso <pablo@netfilter.org> | 2021-07-23 15:18:02 +0300 |
| commit | 32953df7a6eb56bd9b8f18a13034d55f9fc96cfa (patch) | |
| tree | 48e2e8efcadc59cd46cd93bb7ee0e8994804cb9e | |
| parent | 32c3973d808301e7a980f80fee8818fdf7c82b09 (diff) | |
| download | linux-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>
| -rw-r--r-- | net/netfilter/nft_last.c | 20 |
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; |