linux-kernel - Re: [PATCH 2/3] jump_labels: do not use unserialized static_key

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Date:   Tue, 01 Aug 2017 13:52:14 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/3] jump_labels: do not use unserialized
 static_key_enabled

On Tue, 2017-08-01 at 17:24 +0200, Paolo Bonzini wrote:
> Any use of key->enabled (that is static_key_enabled and static_key_count)
> outside jump_label_lock should handle its own serialization.  The only
> two that are not doing so are the UDP encapsulation static keys.  Change
> them to use static_key_enable, which now correctly tests key->enabled under
> the jump label lock.
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  Documentation/static-keys.txt | 5 +++++
>  net/ipv4/udp.c                | 3 +--
>  net/ipv6/udp.c                | 3 +--
>  3 files changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/static-keys.txt b/Documentation/static-keys.txt
> index ef419fd0897f..181998852961 100644
> --- a/Documentation/static-keys.txt
> +++ b/Documentation/static-keys.txt
> @@ -142,6 +142,11 @@ static_branch_inc(), will change the branch back to true. Likewise, if the
>  key is initialized false, a 'static_branch_inc()', will change the branch to
>  true. And then a 'static_branch_dec()', will again make the branch false.
>  
> +The state and the reference count can be retrieved with 'static_key_enabled()'
> +and 'static_key_count()'.  In general, if you use these functions, they
> +should be protected with the same mutex used around the enable/disable
> +or increment/decrement function.
> +
>  Where an array of keys is required, it can be defined as:
>  
>  	DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count);
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 1d6219bf2d6b..74b7810df9fc 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -1644,8 +1644,7 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
>  static struct static_key udp_encap_needed __read_mostly;
>  void udp_encap_enable(void)
>  {
> -	if (!static_key_enabled(&udp_encap_needed))
> -		static_key_slow_inc(&udp_encap_needed);
> +	static_key_enable(&udp_encap_needed);
>  }

Looks good to me, but static_key_enable() is not serialized either ?

I suspect you should have CCed me on patch 1/3 :)