Re: [PATCH v2 net 16/17] net: Fix a data-race around netdev_unregister_timeout_secs.

From: Dmitry Vyukov <dvyukov@google.com>
To: Kuniyuki Iwashima <kuniyu@amazon.com>
Cc: "David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Kuniyuki Iwashima <kuni1840@gmail.com>,
	netdev@vger.kernel.org, Marco Elver <elver@google.com>
Subject: Re: [PATCH v2 net 16/17] net: Fix a data-race around netdev_unregister_timeout_secs.
Date: Thu, 18 Aug 2022 08:53:23 +0200	[thread overview]
Message-ID: <CACT4Y+YJZyfrea7VxHt3varEE0jqJn-d9jaNeE-NXSAXOfi8Ew@mail.gmail.com> (raw)
In-Reply-To: <20220818035227.81567-17-kuniyu@amazon.com>

On Thu, 18 Aug 2022 at 05:57, Kuniyuki Iwashima <kuniyu@amazon.com> wrote:
>
> While reading netdev_unregister_timeout_secs, it can be changed
> concurrently.  Thus, we need to add READ_ONCE() to its reader.
>
> Fixes: 5aa3afe107d9 ("net: make unregister netdev warning timeout configurable")
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> ---
> CC: Dmitry Vyukov <dvyukov@google.com>

Thanks, Kuniyuki.
RIght, since it is a sysctl it can be changed concurrently.

Acked-by: Dmitry Vyukov <dvyukov@google.com>

> ---
>  net/core/dev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 8221322d86db..56c8b0921c9f 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -10284,7 +10284,7 @@ static struct net_device *netdev_wait_allrefs_any(struct list_head *list)
>                                 return dev;
>
>                 if (time_after(jiffies, warning_time +
> -                              netdev_unregister_timeout_secs * HZ)) {
> +                              READ_ONCE(netdev_unregister_timeout_secs) * HZ)) {
>                         list_for_each_entry(dev, list, todo_list) {
>                                 pr_emerg("unregister_netdevice: waiting for %s to become free. Usage count = %d\n",
>                                          dev->name, netdev_refcnt_read(dev));
> --
> 2.30.2
>