[BUG] removing and reinserting imx-media causes kernel to explode

Steve Longerbeam slongerbeam at gmail.com
Sun Aug 18 22:41:00 UTC 2019

On 8/14/19 2:25 AM, Russell King - ARM Linux admin wrote:
> I just did this:
> rmmod imx-media
> modprobe imx-media
> and was greeted by the below kernel messages.

Yes this needs fixing, the CSI needs to check first that it is already 
registered before going through the ->registered() steps. Posting a patch.

>    I don't think this has
> been the first issue I found with the iMX media stuff involving a module
> unload/reload cycle - may I suggest that this is added to the testing
> regime for this code?  Thanks.

I do test module unload/reload cycles, but v4l2-async does not support 
re-registering subdevices unless the subdevice is basically completely 
removed and re-probed, so there won't be a working media device if only 
imx-media is reloaded. So I have always unloaded/reloaded all modules 
for every entity in the graph, i.e.:

rmmod imx6_media imx6_media_csi imx6_mipi_csi2 ov5640 video_mux 

(replace ov5640 with your imx219 sensor).

But I'll make sure to test single module unload/reload cycles in the future.

But note after applying the patch mentioned above to CSI ->registered() 
callback, there are list corruption backtraces, see [1]. The root cause 
is that both media_device_register_entity() and media_entity_pads_init() 
add the same graph objects for the entity's pads, so duplicate pad 
objects are added to the media device pads list. Removing the pad object 
creation in media_device_register_entity() fixes the list corruption. 
Sending a patch for that also.

This is a problem for any entity that sets its ->num_pads to a non-zero 
value before media_device_register_entity() is called. For example, the 
following will produce the same list corruption backtrace:

rmmod video-mux
modprobe video-mux
rmmod video-mux


rmmod imx6-media
modprobe imx6-media
rmmod imx6-media

[  249.387953] WARNING: CPU: 2 PID: 843 at lib/list_debug.c:53 
[  249.396442] list_del corruption. prev->next should be e8fb0510, but 
was e93b5914
[  249.404076] Modules linked in: imx6_media_csi(C) imx6_media(C-) 
imx6_mipi_csi2(C) bnep dw_hdmi_ahb_audio dw_hdmi_cec ov5640 mux_mmio 
video_mux mux_core dw_hdmi_imx dw_hdmi coda_vpu cec imx_vdoa 
videobuf2_vmalloc imx_media_common(C) v4l2_fwnode imx_ldb imxdrm 
imx_ipu_v3 [last unloaded: imx6_media_csi]
[  249.430956] CPU: 2 PID: 843 Comm: rmmod Tainted: G C        
5.3.0-rc4-01115-g62119fd20fda #5
[  249.440115] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[  249.446689] [<c0113a58>] (unwind_backtrace) from [<c010de5c>] 
[  249.454462] [<c010de5c>] (show_stack) from [<c0bdfdcc>] 
[  249.461804] [<c0bdfdcc>] (dump_stack) from [<c0128c28>] 
[  249.468789] [<c0128c28>] (__warn) from [<c0128c98>] 
[  249.476301] [<c0128c98>] (warn_slowpath_fmt) from [<c04e8e00>] 
[  249.485207] [<c04e8e00>] (__list_del_entry_valid) from [<c07e2b8c>] 
[  249.494802] [<c07e2b8c>] (media_gobj_destroy.part.4) from 
[<c07e01d4>] (__media_device_unregister_entity+0xa8/0xcc)
[  249.505259] [<c07e01d4>] (__media_device_unregister_entity) from 
[<c07e0224>] (media_device_unregister_entity+0x2c/0x38)
[  249.516157] [<c07e0224>] (media_device_unregister_entity) from 
[<c07ece34>] (v4l2_device_unregister_subdev+0x90/0xb4)
[  249.526793] [<c07ece34>] (v4l2_device_unregister_subdev) from 
[<c07f9668>] (v4l2_async_cleanup+0x10/0x3c)
[  249.536382] [<c07f9668>] (v4l2_async_cleanup) from [<c07f9730>] 
[  249.546840] [<c07f9730>] (v4l2_async_notifier_unbind_all_subdevs) 
from [<c07f9700>] (v4l2_async_notifier_unbind_all_subdevs+0x6c/0x10c)
[  249.559035] [<c07f9700>] (v4l2_async_notifier_unbind_all_subdevs) 
from [<c07fa3a0>] (__v4l2_async_notifier_unregister.part.4+0xc/0x44)
[  249.571140] [<c07fa3a0>] (__v4l2_async_notifier_unregister.part.4) 
from [<c07fa408>] (v4l2_async_notifier_unregister+0x30/0x50)
[  249.582665] [<c07fa408>] (v4l2_async_notifier_unregister) from 
[<bf03e020>] (imx_media_remove+0x20/0x54 [imx6_media])
[  249.593389] [<bf03e020>] (imx_media_remove [imx6_media]) from 
[<c064a684>] (platform_drv_remove+0x20/0x40)
[  249.603068] [<c064a684>] (platform_drv_remove) from [<c0648b50>] 
[  249.612917] [<c0648b50>] (device_release_driver_internal) from 
[<c0648c7c>] (driver_detach+0x44/0x80)
[  249.622164] [<c0648c7c>] (driver_detach) from [<c0647404>] 
[  249.630287] [<c0647404>] (bus_remove_driver) from [<c01d305c>] 
[  249.638926] [<c01d305c>] (sys_delete_module) from [<c0101000>] 
[  249.647205] Exception stack(0xe90d5fa8 to 0xe90d5ff0)
[  249.652278] 5fa0:                   beed5d6c 00000003 01401134 
00000800 4f13b6f4 00002002
[  249.660475] 5fc0: beed5d6c 00000003 beed5b80 00000081 beed5e78 
00000001 00000000 014010f8
[  249.668669] 5fe0: 0003b2c4 beed5b4c 0001f248 4f1012dc
[  249.673859] irq event stamp: 4113
[  249.677267] hardirqs last  enabled at (4131): [<c018d810>] 
[  249.685125] hardirqs last disabled at (4138): [<c018d490>] 
[  249.692970] softirqs last  enabled at (4154): [<c0102580>] 
[  249.700735] softirqs last disabled at (4165): [<c01306ec>] 
[  249.708134] ---[ end trace 6fde63f19c7b10b8 ]---


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