Re: [PATCH 1/4] scsi: core: constify pointer to scsi_host_template

[Christoph Hellwig]

On Mon, May 09, 2022 at 03:50:33PM +0100, John Garry wrote:
> If you check scsi_device_dev_release(), we try to do a 'get' - if it fails,
> then we nullify hostt->module. I think that is important as then we call
> execute_in_process_context(), whose worker does the 'put'. However, the
> 'put' will get upset if the refcnt was 0, which it would be if the earlier
> 'get' fails - hence the nullify is to avoid that possibility. So whatever
> you do needs to handle that. Details are in f2b85040

Yikes, that code is completely and utterly buggy and does not account
for all the cases why try_module_get can fail.  I think we always have
a reference here and could use __module_get, but what we have is
certainly unsafe and a good reason why the host template should be
constifyed.