Re: [PATCH net-next v9 2/3] net: airoha: fix ETS QoS stats counter underflow and cross-channel corruption

[Jacob Keller <jacob.e.keller@intel.com>]

On 7/21/2026 2:27 AM, Lorenzo Bianconi wrote:
>> On 7/20/2026 3:03 PM, Lorenzo Bianconi wrote:
>>> airoha_qdma_get_tx_ets_stats() has two bugs:
>>> - The hardware counters read via airoha_qdma_rr() are 32-bit values
>>>   but are stored in u64 locals and subtracted from u64 baselines. When
>>>   a 32-bit hardware counter wraps around, the subtraction produces a
>>>   large underflow value passed to _bstats_update().
>>
>> This issue would only be a problem during rollover, which depending on
>> how fast the counts increment may not be a big problem. I could see this
>> not being worth going to net since it could be rare enough that it isn't
>> considered a widespread issue...
>>
>>> - The baseline counters (cpu_tx_packets, fwd_tx_packets) are stored as
>>>   single per-device fields, but airoha_qdma_get_tx_ets_stats() is
>>>   called with different channel values (0-3). Each call reads a
>>>   different channel's hardware counter but overwrites the same
>>>   baseline, corrupting the delta computation for other channels.
>>>
>>
>> However, this issue seems like its going to cause a problem every time
>> you read because any time you use a mix of channels you will get
>> corrupted values?
> 
> Hi Jacob,
> 
> I agree this is a real bug (and it needs to be fixed). However, the real
> use-case is having a single channel per net_device (a single HTB offloaded
> qdisc) and multiple hw queues (connected to the ETS offloaded classes).
> In this scenario we do not trigger this issue.
> 

>> This targets a commit which merged in v6.14, but the patch is part of a
>> series aimed at net-next. Could you explain why this shouldn't be
>> separated out and put as a fix in net? It seems pretty obvious that
>> users can easily reproduce problems by requesting stats from each
>> channel? Or is this not really possible to trigger from userspace until
>> patch 3/3?
> 
> For the reason described above and to avoid any possible conflicts with patch
> 3/3 I decided to add this patch here (adding the proper Fixes tag for the
> backport) but if you prefer I can remove patch 2/3 from this series and send
> it to net. What do you prefer?
> 

If users can't trigger the issue easily in the normal use cases, and the
result is only bad stat values (and not actually corrupt memory etc), I
have no objections to waiting. The scope of the fix is fairly minor and
avoiding the conflicts seems like a reasonable goal.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>

> Regards,
> Lorenzo
>