Re: [PATCH] media: qcom: camss: fix VFE pm domain off

[Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>]

On 11/28/24 12:27, barnabas.czeman@mainlining.org wrote:
> On 2024-11-28 10:10, Vladimir Zapolskiy wrote:
>> On 11/27/24 12:01, Yassine Oudjana wrote:
>>> On 22/11/2024 5:06 am, Barnabás Czémán wrote:
>>>> Fix NULL pointer check before device_link_del
>>>> is called.
>>
>> The intention is clear, but the context of the change is completely
>> lost.
>>
>>>> Fixes: eb73facec2c2 ("media: qcom: camss: Use common VFE
>>>> pm_domain_on/pm_domain_off where applicable")
>>
>> It's invalid, the change is not a fix.
> I don't agree this patch is fixing NULL pointer dereference.
> 
> [   92.989120] Unable to handle kernel NULL pointer dereference at
> virtual address 000000000000032c
> [   92.989170] Mem abort info:
> [   92.989186]   ESR = 0x0000000096000004
> [   92.989203]   EC = 0x25: DABT (current EL), IL = 32 bits
> [   92.989221]   SET = 0, FnV = 0
> [   92.989237]   EA = 0, S1PTW = 0
> [   92.989253]   FSC = 0x04: level 0 translation fault
> [   92.989270] Data abort info:
> [   92.989284]   ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
> [   92.989300]   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
> [   92.989317]   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
> [   92.989335] user pgtable: 4k pages, 48-bit VAs, pgdp=00000001218a8000
> [   92.989354] [000000000000032c] pgd=0000000000000000,
> p4d=0000000000000000
> [   92.989389] Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
> [   92.989408] Modules linked in: q6afe_dai q6asm_dai q6routing q6adm
> q6asm q6afe snd_q6dsp_common panel_lgphilips_sw43101 q6core venus_enc
> venus_dec videobuf2_dma_contig imx318 ak7375 snd_soc_wcd9335
> regmap_slimbus snd_soc_wcd_classh apr snd_soc_apq8096
> snd_soc_qcom_common snd_soc_core qcom_camss msm v4l2_fwnode snd_compress
> ath10k_pci v4l2_async ath10k_core snd_pcm nxp_nci_i2c drm_exec nxp_nci
> venus_core videobuf2_dma_sg snd_timer ath v4l2_mem2mem videobuf2_memops
> mac80211 drm_dp_aux_bus snd gpu_sched nci videobuf2_v4l2 libarc4
> soundcore videodev nfc slim_qcom_ngd_ctrl drm_display_helper hci_uart
> pdr_interface videobuf2_common btqca drm_kms_helper slimbus i2c_qcom_cci
> bluetooth mc qcom_q6v5_pas qcom_q6v5_mss qcom_pil_info qcom_q6v5
> qcom_sysmon qcom_common qmi_helpers mdt_loader socinfo rmtfs_mem
> pwm_ir_tx cfg80211 rfkill zram zsmalloc atmel_mxt_ts drm
> drm_panel_orientation_quirks dm_mod ip_tables
> [   92.989981] CPU: 2 PID: 1365 Comm: pool-megapixels Not tainted
> 6.9.0-rc3+ #10
> [   92.990003] Hardware name: Xiaomi Mi Note 2 (DT)
> [   92.990020] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS
> BTYPE=--)
> [   92.990042] pc : device_link_put_kref+0xc/0xb8
> [   92.990071] lr : device_link_del+0x30/0x48
> [   92.990089] sp : ffff80008a5db9d0
> [   92.990105] x29: ffff80008a5db9d0 x28: 0000000000000001 x27:
> 0000000000000000
> [   92.990143] x26: 0000000000000000 x25: ffff0000e79d9100 x24:
> ffff0000e79d9500
> [   92.990180] x23: ffff0000943f8568 x22: 00000000ffffffff x21:
> 0000000000000000
> [   92.990217] x20: 0000000000000000 x19: ffff800081352498 x18:
> 0000000000000000
> [   92.990253] x17: 0000000000000000 x16: 0000000000000000 x15:
> 0000000000000168
> [   92.990288] x14: 0000000000000000 x13: 0000000000000191 x12:
> ffff800081259d58
> [   92.990324] x11: 0000000000000001 x10: 0000000000000a60 x9 :
> ffff80008a5db7e0
> [   92.990359] x8 : ffff0000e79d9bc0 x7 : 0000000000000004 x6 :
> 0000000000000190
> [   92.990396] x5 : 0000000000000057 x4 : 0000000000000000 x3 :
> 0000000000000000
> [   92.990430] x2 : ffff0000e79d9100 x1 : 0000000000000000 x0 :
> 0000000000000000
> [   92.990466] Call trace:
> [   92.990482]  device_link_put_kref+0xc/0xb8
> [   92.990503]  device_link_del+0x30/0x48
> [   92.990522]  vfe_pm_domain_off+0x24/0x38 [qcom_camss]

vfe_pm_domain_off() shall not be called before vfe_pm_domain_on() call.

If vfe_pm_domain_on() is called and returns failure, then a media pipeline
shall not be started, and vfe_pm_domain_off() shall not be called.

If vfe_pm_domain_on() is called and returns success, then vfe->genpd_link
is not NULL.

Are there any perceptable flaws within the given above reasoning?

Since you've encountered a bug and taking the reasoning from above as
correct, I believe the bug is present somewhere else, and if so, it will
remain unfixed by this change.

> [   92.990566]  vfe_put+0x9c/0xd0 [qcom_camss]
> [   92.990601]  vfe_set_power+0x48/0x58 [qcom_camss]
> [   92.990636]  pipeline_pm_power_one+0x154/0x158 [videodev]
> [   92.990683]  pipeline_pm_power+0x74/0xfc [videodev]
> [   92.990720]  v4l2_pipeline_pm_use+0x54/0x90 [videodev]
> [   92.990757]  v4l2_pipeline_pm_put+0x14/0x34 [videodev]
> [   92.990793]  video_release+0x2c/0x44 [qcom_camss]
> [   92.990828]  v4l2_release+0xe4/0xec [videodev]

Please include the backtrace up to this point into the commit message.

--
Best wishes,
Vladimir