linux-kernel - Re: [PATCH v2] wifi: ath11k: Fix memory reuse logic

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Message-ID: <e5429039-3679-474f-80cc-12f6cc01de09@collabora.com>
Date: Wed, 23 Apr 2025 18:51:36 +0500
From: Muhammad Usama Anjum <usama.anjum@...labora.com>
To: Baochen Qiang <quic_bqiang@...cinc.com>,
 Jeff Johnson <jjohnson@...nel.org>, Kalle Valo <kvalo@...nel.org>,
 Anilkumar Kolli <quic_akolli@...cinc.com>
Cc: kernel@...labora.com, linux-wireless@...r.kernel.org,
 ath11k@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] wifi: ath11k: Fix memory reuse logic

On 4/23/25 1:15 PM, Baochen Qiang wrote:
> 
> 
> On 4/23/2025 2:59 PM, Muhammad Usama Anjum wrote:
>> Firmware requests 2 segments at first. The first segment is of 6799360
>> whose allocation fails due to dma remapping not available. The success
>> is returned to firmware. Then firmware asks for 22 smaller segments
>> instead of 2 big ones. Those get allocated successfully. At suspend/
>> hibernation time, these segments aren't freed as they will be reused
>> by firmware after resuming.
>>
>> After resume the firmware asks for 2 segments again with first segment
>> of 6799360 and vaddr is not NULL. We compare the type and size with
> 
> suggest to rephrase as:
> 
> After resume the firmware asks for 2 segments again with first segment
> of 6799360. Since chunk->vaddr is not NULL, we compare the type and size with
> 
>> previous type and size to know if it can be reused or not.
>> Unfortunately, we detect that it cannot be reuses and this first smaller
> 
> s/reuses/reused/
> 
>> 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
> 
> it is odd with 'from dma' ...
> 
> I think just say 'allocate 6799360 size memory' is good enough.
> 
>> 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 smaller segments again
>> and reuse the remaining 20. Hence we aren't reusing the all 22 small
>> segments, but only 20.
>>
>> This patch is correcting the skip logic when vaddr is set, but size/type
>> 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
>> resume [1] which made us debug why the reuse logic is wrong. Those
> 
> The link is just v1 of this patch, it is not the report. If there is no public report,
> just don't mention it.
> 
>> 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 issue is in the kernel side as because of
>> memory pressure or fragmentation, the dma memory allocation fails. This
>> patch fixes freeing and allocation of 2 smaller chunks.
> 
> I know you are describing why you start to debug this issue. But I don't think it is
> needed in the commit message. No matter kernel allocation fails or succeeds, the issue is
> there, and the description above is sufficient to make the issue clear.
> 
>>
>> Tested-on: WCN6855 WLAN.HSP.1.1-03926.13-QCAHSPSWPL_V2_SILICONZ_CE-2.52297.6
> 
> blank line needed.
> 
>> [1] https://lore.kernel.org/all/b30bc7f6-845d-4f9d-967e-c04a2b5f13f5@collabora.com
>>
>> Signed-off-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
>> ---
>> Changes since v1:
>> - Update description
>>
>> Fixes: 5962f370ce41 ("ath11k: Reuse the available memory after firmware reload")
>> I think we should keep fixes tag as ^ claimed that its adding reuse
>> support. But it left a bug in reuse which we are fixing.
>>
>> Feel free to add it or leave it as it is.
> 
> Jeff, what do you think?
I'll update the description as mentioned. Let's wait for Jeff to review
before I send v3.

> 
>> ---
>>  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,
> 


-- 
Regards,
Usama