Re: [PATCH] Wireguard: Fix data-race in rx/tx counter

[Andrew Lunn <andrew@lunn.ch>]

On Sun, Jun 28, 2026 at 05:38:23PM -0300, Rafael Passos wrote:
> fixes data-race in {rx/tx}_bytes counter for wireguard connection.
> these values were incremented inside a read_lock_bh block, but write
> protections were missing. making them atomic was the simplest way out.
> This was found by syzbot with kcsan.
> 
> Reported-by: syzbot+9ca7674fa7521a3f1bc2@syzkaller.appspotmail.com
> Link: https://syzkaller.appspot.com/bug?extid=9ca7674fa7521a3f1bc2
> Signed-off-by: Rafael Passos <rafael@rcpassos.me>
> ---
> 
> Hi,
> 
> I am posting this patch to better ilustrate the discussion.
> If this is a non-issue, its fine.
> As I mentioned in the previous email, this issue was reported by syzbot,
> but I was not able to reproduce it.
> I am also aware atomic calls may introduce extra cost on older arm cpus.

Atomics are expensive in general, especially on high CPU count
systems. 

Statistic counters tend to be very asymmetric in usage. They are
incremented frequently, maybe per packet, but reported very
infrequently, maybe every minute when an SNMP agent reads them. So the
solution to statistic counters should reflect this. Increment should
be very cheap, reporting them can be expensive.

There are a few different solutions. Per CPU counters is
one. u64_stats_sync.h may help.

Please take a look at other drivers doing statistics. This is a solved
problem, you just need to copy bits of code from somewhere else.

      Andrew