Re: [PATCH] wifi: ath11k: Fix memory reuse logic

[Baochen Qiang <quic_bqiang@quicinc.com>]

On 4/22/2025 3:46 PM, Muhammad Usama Anjum wrote:
> Hi,
> 
> Thank you for excellent review.
> 
> On 4/22/25 7:15 AM, Baochen Qiang wrote:
>>
>>
>> On 4/18/2025 8:09 PM, Muhammad Usama Anjum wrote:
>>> Firmware requests 2 segments at first. 1st segment is of 6799360 whose
>>> allocation fails and we return success to firmware. Then firmware asks
>>
>> Host won't fail in case DMA remapping is enabled. Better to rephrase to make it clear that
>> the big segment allocation fails in case DMA remapping is not working, usually due to
>> IOMMU not present or any necessary kernel config not enabled.
> IOMMU is turned off. I'll make description better.
> 
>>
>>> for 22 smaller segments. Those get allocated. At suspend/hibernation
>>> time, these segments aren't freed as they are reused by firmware.
>>>
>>> After resume the firmware asks for 2 segments again with first segment
>>> of 6799360 and with same vaddr of the first smaller segment which we had
>>
>> Not follow you here. What do you mean by 'same vaddr'? firmware does not care about vaddr
>> at all.
> So we get request to allocate memory of size = 6799360 and vaddr =
> 0xABC). We fail it. Then we get request to allocate memory of size =
> 500000 and vaddr is same 0xABC which gets allocated successfully.
> 
> When we resume, firmware asks again for 6799360 with 0xABC vaddr even
> though we had allocated memory of 500000 size at 0xABC. I'm referring to
> this vaddr that its same.

OK, get your point. But like I said, firmware doesn't case about vaddr, so it is not
asking for a 'same vaddr'.

IMO just mentioning vaddr is not NULL is sufficient.

> 
>>
>>> allocated. Hence vaddr isn't NULL and we compare the type and size if it
>>> can be reused. Unfornately, we detect that we cannot reuse it and this
>>
>> s/Unfornately/Unfortunately/
>>
>>> first smaller segment is freed. Then we continue to allocate 6799360 size
>>> memory from dma which fails and we call ath11k_qmi_free_target_mem_chunk()
>>> which frees the second smaller segment as well. Later success is returned
>>> to firmware which asks for 22 smaller segments again. But as we had freed
>>> 2 segments already, we'll allocate the first 2 new segments again and
>>> reuse the remaining 20.
>>>
>>> This patch is correctiong the skip logic when vaddr is set, but size/type
>>
>> s/correctiong/correcting/
>>
>>> don't match. In this case, we should use the same skip and success logic
>>> as used when dma_alloc_coherent fails without freeing the memory area.
>>>
>>> We had got reports that memory allocation in this function failed at
>>
>> any public link to the report?
> There's no public report. I've attached the logs. You'll find following
> error logs in it:
> 
> ath11k_pci 0000:03:00.0: failed to allocate dma memory for qmi (524288 B
> type 1)
> ath11k_pci 0000:03:00.0: failed to allocate qmi target memory: -22
> 
> 
>>
>>> resume which made us debug why the reuse logic is wrong. Those failures
>>> weren't because of the bigger chunk allocation failure as they are
>>> skipped. Rather these failures were because of smaller chunk allocation
>>> failures. This patch fixes freeing and allocation of 2 smaller chunks.
>>
>> any you saying kernels fail to alloc a smaller chunk? why? is system memory exhausted or
>> too fragmented?
> Yes, the smaller chunk doesn't get allocated. I've not been able to
> reproduce it on my setup. Both system memory exhaustion and
> fragmentation are the suspects.

so it is kernel failing to allocate the buffer, not any issue in ath12k leading to this.
Please help make this clear to avoid confusion.

> 
>>
>>>
>>> Tested-on: QCNFA765 WLAN.HSP.1.1-03926.13-QCAHSPSWPL_V2_SILICONZ_CE-2.52297.6
>>
>> QCNFA765 is not an official chip name. please use WCN6855.
> Okay. I'll fix all of these mistakes.
> 
>>
>>>
>>> Fixes: 5962f370ce41 ("ath11k: Reuse the available memory after firmware reload")
>>
>> I don't think a Fixes tag apply here. As IMO this is not really an issue, it is just not
>> doing well.
>>
>>> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
>>> ---
>>>  drivers/net/wireless/ath/ath11k/qmi.c | 10 +++++++++-
>>>  1 file changed, 9 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/wireless/ath/ath11k/qmi.c b/drivers/net/wireless/ath/ath11k/qmi.c
>>> index 47b9d4126d3a9..3c26f4dcf5d29 100644
>>> --- a/drivers/net/wireless/ath/ath11k/qmi.c
>>> +++ b/drivers/net/wireless/ath/ath11k/qmi.c
>>> @@ -1990,8 +1990,16 @@ static int ath11k_qmi_alloc_target_mem_chunk(struct ath11k_base *ab)
>>>  		 */
>>>  		if (chunk->vaddr) {
>>>  			if (chunk->prev_type == chunk->type &&
>>> -			    chunk->prev_size == chunk->size)
>>> +			    chunk->prev_size == chunk->size) {
>>>  				continue;
>>> +			} else if (ab->qmi.mem_seg_count <= ATH11K_QMI_FW_MEM_REQ_SEGMENT_CNT) {
>>> +				ath11k_dbg(ab, ATH11K_DBG_QMI,
>>> +					   "size/type mismatch (current %d %u) (prev %d %u), try later with small size\n",
>>> +					    chunk->size, chunk->type,
>>> +					    chunk->prev_size, chunk->prev_type);
>>> +				ab->qmi.target_mem_delayed = true;
>>> +				return 0;
>>> +			}
>>>  
>>>  			/* cannot reuse the existing chunk */
>>>  			dma_free_coherent(ab->dev, chunk->prev_size,
>>
>> actual code change LGTM.
>>
>>
> 
>