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

[Mike Snitzer <snitzer@redhat.com>]

On Mon, Feb 21 2022 at  5:36P -0500,
Faqiang Zhu <faqiang.zhu@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@lst.de> hch@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().

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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