[dm-devel] a potential issue for bow_target after "dm: delay registering the gendisk" applied

[Sweet Tea Dorminy]

On 2/21/22 11:42, Mike Snitzer wrote:
> On Mon, Feb 21 2022 at  5:36P -0500,
> Faqiang Zhu <faqiang.zhu at nxp.com> wrote:
>
>> Hi Christoph,
>>
>>   
>>
>> Recently when I use kernel5.15 with android, an issue related to bow_target
>> is found with below log:
>>
>>   
>>
>> [    8.935429][    T1] kobject_add_internal failed for bow (error: -2
>> parent: (null))
>>
>>   
>>
>> The call trace to the preceding log is as below:
>>
>> dm_ctl_ioctl
>>
>>   -> ctl_ioctl
>>
>>     -> lookup_ioctl    // returns the table_load function pointer
>>
>>        table_load
>>
>>          -> populate_table
>>
>>               -> dm_table_add_target
>>
>>                    -> dm_bow_ctr
>>
>>                         -> kobject_init_and_add
>>
>>                              -> kobject_add_varg
>>
>>                                   -> kobject_add_internal
>>
>>   
>>
>>   
>>
>> Compared to kernel5.10, then I found it's related to below patch. The
>> gendisk, it's not registered yet, its kobject is not in sysfs, so its child
>> "bow" kobject cannot be added to the kernel.
>>
>> commit 89f871af1b26d98d983cba7ed0e86effa45ba5f8
>>
>> Author: Christoph Hellwig  <mailto:hch at lst.de> hch at lst.de
>>
>> Date:   Wed Aug 4 11:41:46 2021 +0200
>>
>>   
>>
>>      dm: delay registering the gendisk
>>
>>   
>>
>>   
>>
>> Is this an issue? if it is, is there any patch to fix it? if it is not, then
>> what is the right way to use the bow_target in userspace?
>>
> It is an issue for this out-of-tree dm-bow target.  Likely needs to be
> fixed by adding a new DM target operation to 'struct target_type' that
> would get called by DM core at end of dm_setup_md_queue().


Might also be able to just move the sysfs initialization to first 
preresume time, as the out-of-tree module VDO does? 
https://github.com/dm-vdo/kvdo/commit/27bf63255af9e01736ca657df2fa1a03dcf124b8 


Sweet Tea

>
> Or dm-bow discontinues using sysfs for whatever and convert to using
> DM messages (with .message) and exposing associated state via .status
>
> Mike
>
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