* [PATCH net] net/tcp_fastopen: fix data races around tfo_active_disable_stamp
@ 2021-07-19 9:12 Eric Dumazet
2021-07-19 15:40 ` Wei Wang
2021-07-19 17:20 ` patchwork-bot+netdevbpf
0 siblings, 2 replies; 3+ messages in thread
From: Eric Dumazet @ 2021-07-19 9:12 UTC (permalink / raw)
To: David S . Miller, Jakub Kicinski
Cc: netdev, Eric Dumazet, Eric Dumazet, Wei Wang, Yuchung Cheng,
Neal Cardwell
From: Eric Dumazet <edumazet@google.com>
tfo_active_disable_stamp is read and written locklessly.
We need to annotate these accesses appropriately.
Then, we need to perform the atomic_inc(tfo_active_disable_times)
after the timestamp has been updated, and thus add barriers
to make sure tcp_fastopen_active_should_disable() wont read
a stale timestamp.
Fixes: cf1ef3f0719b ("net/tcp_fastopen: Disable active side TFO in certain scenarios")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Wei Wang <weiwan@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
---
net/ipv4/tcp_fastopen.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 47c32604d38fca960d2cd56f3588bfd2e390b789..b32af76e21325373126b51423496e3b8d47d97ff 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -507,8 +507,15 @@ void tcp_fastopen_active_disable(struct sock *sk)
{
struct net *net = sock_net(sk);
+ /* Paired with READ_ONCE() in tcp_fastopen_active_should_disable() */
+ WRITE_ONCE(net->ipv4.tfo_active_disable_stamp, jiffies);
+
+ /* Paired with smp_rmb() in tcp_fastopen_active_should_disable().
+ * We want net->ipv4.tfo_active_disable_stamp to be updated first.
+ */
+ smp_mb__before_atomic();
atomic_inc(&net->ipv4.tfo_active_disable_times);
- net->ipv4.tfo_active_disable_stamp = jiffies;
+
NET_INC_STATS(net, LINUX_MIB_TCPFASTOPENBLACKHOLE);
}
@@ -526,10 +533,16 @@ bool tcp_fastopen_active_should_disable(struct sock *sk)
if (!tfo_da_times)
return false;
+ /* Paired with smp_mb__before_atomic() in tcp_fastopen_active_disable() */
+ smp_rmb();
+
/* Limit timeout to max: 2^6 * initial timeout */
multiplier = 1 << min(tfo_da_times - 1, 6);
- timeout = multiplier * tfo_bh_timeout * HZ;
- if (time_before(jiffies, sock_net(sk)->ipv4.tfo_active_disable_stamp + timeout))
+
+ /* Paired with the WRITE_ONCE() in tcp_fastopen_active_disable(). */
+ timeout = READ_ONCE(sock_net(sk)->ipv4.tfo_active_disable_stamp) +
+ multiplier * tfo_bh_timeout * HZ;
+ if (time_before(jiffies, timeout))
return true;
/* Mark check bit so we can check for successful active TFO
--
2.32.0.402.g57bb445576-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH net] net/tcp_fastopen: fix data races around tfo_active_disable_stamp
2021-07-19 9:12 [PATCH net] net/tcp_fastopen: fix data races around tfo_active_disable_stamp Eric Dumazet
@ 2021-07-19 15:40 ` Wei Wang
2021-07-19 17:20 ` patchwork-bot+netdevbpf
1 sibling, 0 replies; 3+ messages in thread
From: Wei Wang @ 2021-07-19 15:40 UTC (permalink / raw)
To: Eric Dumazet
Cc: David S . Miller, Jakub Kicinski, netdev, Eric Dumazet,
Yuchung Cheng, Neal Cardwell
On Mon, Jul 19, 2021 at 2:12 AM Eric Dumazet <eric.dumazet@gmail.com> wrote:
>
> From: Eric Dumazet <edumazet@google.com>
>
> tfo_active_disable_stamp is read and written locklessly.
> We need to annotate these accesses appropriately.
>
> Then, we need to perform the atomic_inc(tfo_active_disable_times)
> after the timestamp has been updated, and thus add barriers
> to make sure tcp_fastopen_active_should_disable() wont read
> a stale timestamp.
>
> Fixes: cf1ef3f0719b ("net/tcp_fastopen: Disable active side TFO in certain scenarios")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Wei Wang <weiwan@google.com>
> Cc: Yuchung Cheng <ycheng@google.com>
> Cc: Neal Cardwell <ncardwell@google.com>
> ---
Thanks Eric!
Acked-by: Wei Wang <weiwan@google.com>
> net/ipv4/tcp_fastopen.c | 19 ++++++++++++++++---
> 1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
> index 47c32604d38fca960d2cd56f3588bfd2e390b789..b32af76e21325373126b51423496e3b8d47d97ff 100644
> --- a/net/ipv4/tcp_fastopen.c
> +++ b/net/ipv4/tcp_fastopen.c
> @@ -507,8 +507,15 @@ void tcp_fastopen_active_disable(struct sock *sk)
> {
> struct net *net = sock_net(sk);
>
> + /* Paired with READ_ONCE() in tcp_fastopen_active_should_disable() */
> + WRITE_ONCE(net->ipv4.tfo_active_disable_stamp, jiffies);
> +
> + /* Paired with smp_rmb() in tcp_fastopen_active_should_disable().
> + * We want net->ipv4.tfo_active_disable_stamp to be updated first.
> + */
> + smp_mb__before_atomic();
> atomic_inc(&net->ipv4.tfo_active_disable_times);
> - net->ipv4.tfo_active_disable_stamp = jiffies;
> +
> NET_INC_STATS(net, LINUX_MIB_TCPFASTOPENBLACKHOLE);
> }
>
> @@ -526,10 +533,16 @@ bool tcp_fastopen_active_should_disable(struct sock *sk)
> if (!tfo_da_times)
> return false;
>
> + /* Paired with smp_mb__before_atomic() in tcp_fastopen_active_disable() */
> + smp_rmb();
> +
> /* Limit timeout to max: 2^6 * initial timeout */
> multiplier = 1 << min(tfo_da_times - 1, 6);
> - timeout = multiplier * tfo_bh_timeout * HZ;
> - if (time_before(jiffies, sock_net(sk)->ipv4.tfo_active_disable_stamp + timeout))
> +
> + /* Paired with the WRITE_ONCE() in tcp_fastopen_active_disable(). */
> + timeout = READ_ONCE(sock_net(sk)->ipv4.tfo_active_disable_stamp) +
> + multiplier * tfo_bh_timeout * HZ;
> + if (time_before(jiffies, timeout))
> return true;
>
> /* Mark check bit so we can check for successful active TFO
> --
> 2.32.0.402.g57bb445576-goog
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH net] net/tcp_fastopen: fix data races around tfo_active_disable_stamp
2021-07-19 9:12 [PATCH net] net/tcp_fastopen: fix data races around tfo_active_disable_stamp Eric Dumazet
2021-07-19 15:40 ` Wei Wang
@ 2021-07-19 17:20 ` patchwork-bot+netdevbpf
1 sibling, 0 replies; 3+ messages in thread
From: patchwork-bot+netdevbpf @ 2021-07-19 17:20 UTC (permalink / raw)
To: Eric Dumazet; +Cc: davem, kuba, netdev, edumazet, weiwan, ycheng, ncardwell
Hello:
This patch was applied to netdev/net.git (refs/heads/master):
On Mon, 19 Jul 2021 02:12:18 -0700 you wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> tfo_active_disable_stamp is read and written locklessly.
> We need to annotate these accesses appropriately.
>
> Then, we need to perform the atomic_inc(tfo_active_disable_times)
> after the timestamp has been updated, and thus add barriers
> to make sure tcp_fastopen_active_should_disable() wont read
> a stale timestamp.
>
> [...]
Here is the summary with links:
- [net] net/tcp_fastopen: fix data races around tfo_active_disable_stamp
https://git.kernel.org/netdev/net/c/6f20c8adb181
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-07-19 9:12 [PATCH net] net/tcp_fastopen: fix data races around tfo_active_disable_stamp Eric Dumazet
2021-07-19 15:40 ` Wei Wang
2021-07-19 17:20 ` patchwork-bot+netdevbpf
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