netdev - Re: [PATCH] ipv6: Use local variable for ifa->flags in inet6_fill

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Message-ID: <CANn89iKdafBUvrCuy2rOu5Hg8qQrFxmD9JU5KuE=zbntMvQK8g@mail.gmail.com>
Date: Mon, 4 Nov 2024 14:54:03 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Zilin Guan <zilinguan811@...il.com>
Cc: davem@...emloft.net, dsahern@...nel.org, kuba@...nel.org, 
	pabeni@...hat.com, horms@...nel.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipv6: Use local variable for ifa->flags in inet6_fill_ifaddr

On Mon, Nov 4, 2024 at 2:25 PM Zilin Guan <zilinguan811@...il.com> wrote:
>
> Currently, the inet6_fill_ifaddr() function reads the value of ifa->flags
> using READ_ONCE() and stores it in the local variable flags. However,
> the subsequent call to put_ifaddrmsg() uses ifa->flags again instead of
> the already read local variable. This re-read is unnecessary because
> no other thread can modify ifa->flags between the initial READ_ONCE()
> and the subsequent use in put_ifaddrmsg().

I do not think this last sentence is true. I would rephrase this or remove it.

Otherwise, patch looks fine to me, thanks.


>
> Signed-off-by: Zilin Guan <zilinguan811@...il.com>
> ---
>  net/ipv6/addrconf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 94dceac52884..c4b080471b39 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -5143,7 +5143,7 @@ static int inet6_fill_ifaddr(struct sk_buff *skb,
>                 return -EMSGSIZE;
>
>         flags = READ_ONCE(ifa->flags);
> -       put_ifaddrmsg(nlh, ifa->prefix_len, ifa->flags, rt_scope(ifa->scope),
> +       put_ifaddrmsg(nlh, ifa->prefix_len, flags, rt_scope(ifa->scope),
>                       ifa->idev->dev->ifindex);
>
>         if (args->netnsid >= 0 &&
> --
> 2.34.1
>