netdev - Re: [PATCH net] net: bridge: annotate data-race in br_fdb

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Message-ID: <5452a132-448c-43db-b6f2-53f0f207dc67@blackwall.org>
Date: Wed, 7 Jan 2026 09:03:01 +0200
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Eric Dumazet <edumazet@...gle.com>, "David S . Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, netdev@...r.kernel.org,
 eric.dumazet@...il.com
Subject: Re: [PATCH net] net: bridge: annotate data-race in br_fdb_update()

On 07/01/2026 09:00, Nikolay Aleksandrov wrote:
> On 06/01/2026 23:26, Nikolay Aleksandrov wrote:
>> On 06/01/2026 21:40, Eric Dumazet wrote:
>>> fdb->updated is read and written locklessly.
>>>
>>> Add READ_ONCE()/WRITE_ONCE() annotations.
>>>
>>> Fixes: 31cbc39b6344 ("net: bridge: add option to allow activity 
>>> notifications for any fdb entries")
>>> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>>> Cc: Nikolay Aleksandrov <razor@...ckwall.org>
>>> ---
>>>   net/bridge/br_fdb.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
>>> index 
>>> 58d22e2b85fc3551bd5aec9c20296ddfcecaa040..e7bd20f0e8d6b7b24aef43d7bed34adf171c34a8 100644
>>> --- a/net/bridge/br_fdb.c
>>> +++ b/net/bridge/br_fdb.c
>>> @@ -1002,8 +1002,8 @@ void br_fdb_update(struct net_bridge *br, 
>>> struct net_bridge_port *source,
>>>               unsigned long now = jiffies;
>>>               bool fdb_modified = false;
>>> -            if (now != fdb->updated) {
>>> -                fdb->updated = now;
>>> +            if (now != READ_ONCE(fdb->updated)) {
>>> +                WRITE_ONCE(fdb->updated, now);
>>>                   fdb_modified = __fdb_mark_active(fdb);
>>>               }
>>
>> Thanks,
>> Acked-by: Nikolay Aleksandrov <razor@...ckwall.org>
> 
> Actually on second thought, ->updated is used lockless in a few more
> places, e.g. br_fdb_fillbuf(), fdb_fill_info(), br_fdb_cleanup().
> 

I mean I see the subject, but since this patch will get backported
perhaps we can annotate all instances in one go.

Cheers,
  Nik