netdev - Re: [PATCH v3 net 05/17] ratelimit: Fix data-races in __

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Date:   Mon, 22 Aug 2022 12:00:11 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Kuniyuki Iwashima <kuniyu@...zon.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Kuniyuki Iwashima <kuni1840@...il.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v3 net 05/17] ratelimit: Fix data-races in ___ratelimit().

On Thu, Aug 18, 2022 at 11:29 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> While reading rs->interval and rs->burst, they can be changed
> concurrently.  Thus, we need to add READ_ONCE() to their readers.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> ---
>  lib/ratelimit.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/lib/ratelimit.c b/lib/ratelimit.c
> index e01a93f46f83..b59a1d3d0cc3 100644
> --- a/lib/ratelimit.c
> +++ b/lib/ratelimit.c
> @@ -26,10 +26,12 @@
>   */
>  int ___ratelimit(struct ratelimit_state *rs, const char *func)
>  {
> +       int interval = READ_ONCE(rs->interval);
> +       int burst = READ_ONCE(rs->burst);

I thought rs->interval and rs->burst were constants...

Can you point to the part where they are changed ?

Ideally such a patch should also add corresponding WRITE_ONCE(), and
comments to pair them,
 this would really help reviewing it.


>         unsigned long flags;
>         int ret;
>
> -       if (!rs->interval)
> +       if (!interval)
>                 return 1;
>
>         /*
> @@ -44,7 +46,7 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
>         if (!rs->begin)
>                 rs->begin = jiffies;
>
> -       if (time_is_before_jiffies(rs->begin + rs->interval)) {
> +       if (time_is_before_jiffies(rs->begin + interval)) {
>                 if (rs->missed) {
>                         if (!(rs->flags & RATELIMIT_MSG_ON_RELEASE)) {
>                                 printk_deferred(KERN_WARNING
> @@ -56,7 +58,7 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
>                 rs->begin   = jiffies;
>                 rs->printed = 0;
>         }
> -       if (rs->burst && rs->burst > rs->printed) {
> +       if (burst && burst > rs->printed) {
>                 rs->printed++;
>                 ret = 1;
>         } else {
> --
> 2.30.2
>