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

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Message-ID: <5ae72a5c-798a-4c57-b344-02b231cb881c@quicinc.com>
Date: Tue, 22 Apr 2025 10:15:40 +0800
From: Baochen Qiang <quic_bqiang@...cinc.com>
To: Muhammad Usama Anjum <usama.anjum@...labora.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] wifi: ath11k: Fix memory reuse logic



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.

> 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.

> 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?

> 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?

> 
> 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.

> 
> 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@...labora.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.