Re: [PATCH v2] driver core: Fix bus_type.match() error handling

[Bart Van Assche <bvanassche@acm.org>]

On 8/20/22 04:48, Guenter Roeck wrote:
> INFO: task init:283 blocked for more than 122 seconds.
>        Tainted: G                 N 6.0.0-rc1-00303-g963a70bee588 #3
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:init            state:D stack:    0 pid:  283 ppid:     1 flags:0x00000000
>   __schedule from schedule+0x70/0x118
>   schedule from scsi_remove_host+0x178/0x1c4
>   scsi_remove_host from usb_stor_disconnect+0x40/0xe8
>   usb_stor_disconnect from usb_unbind_interface+0x78/0x274
>   usb_unbind_interface from device_release_driver_internal+0x1a4/0x230
>   device_release_driver_internal from bus_remove_device+0xd0/0x100
>   bus_remove_device from device_del+0x174/0x3ec
>   device_del from usb_disable_device+0xcc/0x178
>   usb_disable_device from usb_disconnect+0xcc/0x274
>   usb_disconnect from usb_disconnect+0x98/0x274
>   usb_disconnect from usb_remove_hcd+0xd0/0x16c
>   usb_remove_hcd from host_stop+0x38/0xa8
>   host_stop from ci_hdrc_remove+0x40/0x134
>   ci_hdrc_remove from platform_remove+0x24/0x54
>   platform_remove from device_release_driver_internal+0x1a4/0x230
>   device_release_driver_internal from bus_remove_device+0xd0/0x100
>   bus_remove_device from device_del+0x174/0x3ec
>   device_del from platform_device_del.part.0+0x10/0x78
>   platform_device_del.part.0 from platform_device_unregister+0x18/0x28
>   platform_device_unregister from ci_hdrc_remove_device+0xc/0x24
>   ci_hdrc_remove_device from ci_hdrc_imx_remove+0x28/0xfc
>   ci_hdrc_imx_remove from device_shutdown+0x178/0x230
>   device_shutdown from __do_sys_reboot+0x168/0x258
>   __do_sys_reboot from ret_fast_syscall+0x0/0x1c

Hi Guenter,

Thank you for having shared this information. I think this deadlock is 
the result of holding a reference on /dev/sda (by the mount() system 
call) while calling scsi_remove_host().

It seems wrong to me that ci_hdrc_imx_shutdown() calls 
ci_hdrc_imx_remove() - I think that function should only do the minimum 
that is required to prepare for shutdown instead of calling 
scsi_remove_host() indirectly.

That being said, the patch series "scsi: core: Call 
blk_mq_free_tag_set() earlier" probably will have to be reverted because 
of the following deadlock reported by syzbot: 
https://lore.kernel.org/linux-scsi/000000000000b5187d05e6c08086@google.com/

Thanks,

Bart.