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From: Kalle Valo <kvalo@kernel.org>
To: Baochen Qiang <quic_bqiang@quicinc.com>
Cc: <ath12k@lists.infradead.org>,  <linux-wireless@vger.kernel.org>
Subject: Re: [PATCH] wifi: ath12k: fix kernel crash during resume
References: <20240419034034.2842-1-quic_bqiang@quicinc.com>
	<87cyqmhtoi.fsf@kernel.org>
Date: Fri, 19 Apr 2024 07:38:11 +0300
In-Reply-To: <87cyqmhtoi.fsf@kernel.org> (Kalle Valo's message of "Fri, 19 Apr
	2024 07:18:05 +0300")
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Kalle Valo <kvalo@kernel.org> writes:

> Baochen Qiang <quic_bqiang@quicinc.com> writes:
>
>> Currently during resume, QMI target memory is not properly handled, resulting
>> in kernel crash in case DMA remap is not supported:
>>
>> BUG: Bad page state in process kworker/u16:54  pfn:36e80
>> page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x36e80
>> page dumped because: nonzero _refcount
>> Call Trace:
>>  bad_page
>>  free_page_is_bad_report
>>  __free_pages_ok
>>  __free_pages
>>  dma_direct_free
>>  dma_free_attrs
>>  ath12k_qmi_free_target_mem_chunk
>>  ath12k_qmi_msg_mem_request_cb
>>
>> The reason is:
>> Once ath12k module is loaded, firmware sends memory request to host. In case
>> DMA remap not supported, ath12k refuses the first request due to failure in
>> allocating with large segment size:
>>
>> ath12k_pci 0000:04:00.0: qmi firmware request memory request
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 7077888
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 8454144
>> ath12k_pci 0000:04:00.0: qmi dma allocation failed (7077888 B type 1), will try later with small size
>> ath12k_pci 0000:04:00.0: qmi delays mem_request 2
>> ath12k_pci 0000:04:00.0: qmi firmware request memory request
>>
>> Later firmware comes back with more but small segments and allocation
>> succeeds:
>>
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 262144
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 524288
>> ath12k_pci 0000:04:00.0: qmi mem seg type 4 size 65536
>> ath12k_pci 0000:04:00.0: qmi mem seg type 1 size 524288
>>
>> Now ath12k is working. If suspend is triggered, firmware will be reloaded
>> during resume. As same as before, firmware requests two large segments at
>> first. In ath12k_qmi_msg_mem_request_cb() segment count and size are
>> assigned:
>>
>> 	ab->qmi.mem_seg_count == 2
>> 	ab->qmi.target_mem[0].size == 7077888
>> 	ab->qmi.target_mem[1].size == 8454144
>>
>> Then allocation failed like before and ath12k_qmi_free_target_mem_chunk()
>> is called to free all allocated segments. Note the first segment is skipped
>> because its v.addr is cleared due to allocation failure:
>>
>> 	chunk->v.addr = dma_alloc_coherent()
>>
>> Also note that this leaks that segment because it has not been freed.
>>
>> While freeing the second segment, a size of 8454144 is passed to
>> dma_free_coherent(). However remember that this segment is allocated at
>> the first time firmware is loaded, before suspend. So its real size is
>> 524288, much smaller than 8454144. As a result kernel found we are freeing
>> some memory which is in use and thus crashed.
>>
>> So one possible fix would be to free those segments during suspend. This
>> works because with them freed, ath12k_qmi_free_target_mem_chunk() does
>> nothing: all segment addresses are NULL so dma_free_coherent() is not called.
>>
>> But note that ath11k has similar logic but never hits this issue. Reviewing
>> code there shows the luck comes from QMI memory reuse logic. So the decision
>> is to port it to ath12k. Like in ath11k, the crash is avoided by adding
>> prev_size to target_mem_chunk structure and caching real segment size in it,
>> then prev_size instead of current size is passed to dma_free_coherent(),
>> no unexpected memory is freed now.
>>
>> Also reuse m3 buffer.
>>
>> Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0-03427-QCAHMTSWPL_V1.0_V2.0_SILICONZ-1.15378.4
>> Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3
>>
>> Fixes: 64430ddfb132 ("wifi: ath12k: support suspend/resume")

ERROR: Commit id not found from current branch: Fixes: 64430ddfb132 ("wifi: ath12k: support suspend/resume")

Do note that commit ids in the pending branch are not stable so fixes
tags cannot be used for those commits.

>> Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
>
> To keep git bisect clean should this patch be applied before applying
> the suspend patchset? No need resend or anything, just checking what
> should be the correct order.

Ah, I just checked and it looks like this patch depends on the suspend
patchset. I now applied this patch to pendign branch
(ath-pending-202404190433).

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