Re: [PATCH] wifi: ath12k: fix kernel crash during resume

[Kalle Valo <kvalo@kernel.org>]

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")
> 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.

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