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

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Message-ID: <6a7cb6d7-b337-4b21-b236-5419b785dc90@blackwall.org>
Date: Wed, 7 Jan 2026 09:00:34 +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 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().