Re: [PATCH net-next] net: dev_addr_lists: don't WARN on GFP_ATOMIC kmalloc failure in netif_rx_mode_run

[Zijing yin <yzjaurora@gmail.com>]

Thanks! I will attach it accordingly. 

On 19.05.2026 14:22, Jiayuan Chen wrote:
> On Tue, May 19, 2026 at 02:11:53PM +0800, Zijing yin wrote:
>> Thank you so much for the feedback! I will address these comments in the 
>> next version. This is not found by syzbot by the way.
> 
> There has the a syzbot report now:
> https://syzkaller.appspot.com/bug?extid=f2421634072a4b47071e
> 
>>
>> Hope you have a great day!
>>
>> On 19.05.2026 13:22, Jakub Sitnicki wrote:
>>> On Tue, May 19, 2026 at 02:55 AM -07, Zijing Yin wrote:
>>>> netif_rx_mode_run() fires netdev_WARN() when netif_addr_lists_snapshot()
>>>> returns non-zero. The only path to a non-zero return is -ENOMEM from
>>>> __hw_addr_create() failing its kmalloc(GFP_ATOMIC) -- syzkaller hits it
>>>> via failslab, and it can also be reached under real memory pressure.
>>>>
>>>> This is the only allocator-failure site in this file that WARNs.
>>>> __hw_addr_create() itself, and every other caller of it in this file
>>>> (__hw_addr_add_ex(), dev_uc_add_excl(), dev_uc_add(), dev_mc_add(), ...)
>>>> just propagate the -ENOMEM silently. GFP_ATOMIC is a may-fail allocator;
>>>> callers are required to handle NULL, so a returned -ENOMEM here is an
>>>> expected runtime condition, not an invariant violation.
>>>>
>>>> The miss is self-healing: any subsequent change to dev->uc / dev->mc
>>>> (every dev_{uc,mc}_{add,del}, IFF_PROMISC flip, etc.) calls
>>>> __dev_set_rx_mode() -> netif_rx_mode_queue(), which re-queues the device
>>>> and retries the sync. The only cost of a failed attempt is one stale
>>>> rx-mode window until the next update; nothing in the kernel relies on
>>>> this attempt succeeding.
>>>>
>>>> Demote to net_err_ratelimited() so the condition stays observable in
>>>> dmesg without tripping panic_on_warn.
>>>>
>>>> Reproducer (syzkaller .prog format with setup notes): 
>>>> https://pastebin.com/t7AQKx9v
>>>>
>>>> Fixes: 3554b4345d85 ("net: introduce ndo_set_rx_mode_async and netdev_rx_mode_work")
>>>> Signed-off-by: Zijing Yin <yzjaurora@gmail.com>
>>>> ---
>>>>  net/core/dev_addr_lists.c | 3 ++-
>>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/net/core/dev_addr_lists.c b/net/core/dev_addr_lists.c
>>>> index d73fcb0c6..c6fdcac74 100644
>>>> --- a/net/core/dev_addr_lists.c
>>>> +++ b/net/core/dev_addr_lists.c
>>>> @@ -1275,7 +1275,8 @@ static void netif_rx_mode_run(struct net_device *dev)
>>>>  		err = netif_addr_lists_snapshot(dev, &uc_snap, &mc_snap,
>>>>  						&uc_ref, &mc_ref);
>>>>  		if (err) {
>>>> -			netdev_WARN(dev, "failed to sync uc/mc addresses\n");
>>>> +			net_err_ratelimited("%s: failed to sync uc/mc addresses\n",
>>>> +					    netdev_name(dev));
>>>>  			netif_addr_unlock_bh(dev);
>>>>  			return;
>>>>  		}
>>>
>>> 1) I'd go with net_warn_ratelimited() instead. The promoted message
>>> level in syslog might cause operational pain, and as you say the
>>> condition is self-healing. Seems unwarranted.
>>>
>>> 2) Since it has a Fixes tag, should probably be sumitted for 'net' tree.
>>>
>>> 3) Was this reported by syzbot? If so, there should also be Reported-by
>>> and Closes tags.
>>