Re: [PATCH V3] scsi: core: put LLD module refcnt after SCSI device is released

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Sep 30, 2021 at 08:44:15PM +0800, Ming Lei wrote:
> SCSI host release is triggered when SCSI device is freed, and we have to
> make sure that LLD module won't be unloaded before SCSI host instance is
> released because shost->hostt is required in host release handler.
> 
> So make sure to put LLD module refcnt after SCSI device is released.

What is a "LLD"?

> Fix one kernel panic of 'BUG: unable to handle page fault for address'
> reported by Changhui and Yi.
> 
> Reported-by: Changhui Zhong <czhong@redhat.com>
> Reported-by: Yi Zhang <yi.zhang@redhat.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  drivers/scsi/scsi.c        |  4 +++-
>  drivers/scsi/scsi_sysfs.c  | 12 ++++++++++++
>  include/scsi/scsi_device.h |  1 +
>  3 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index b241f9e3885c..291ecc33b1fe 100644
> --- a/drivers/scsi/scsi.c
> +++ b/drivers/scsi/scsi.c
> @@ -553,8 +553,10 @@ EXPORT_SYMBOL(scsi_device_get);
>   */
>  void scsi_device_put(struct scsi_device *sdev)
>  {
> -	module_put(sdev->host->hostt->module);
> +	struct module *mod = sdev->host->hostt->module;
> +
>  	put_device(&sdev->sdev_gendev);
> +	module_put(mod);
>  }
>  EXPORT_SYMBOL(scsi_device_put);
>  
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index 86793259e541..9ada26814011 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -449,9 +449,16 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
>  	struct scsi_vpd *vpd_pg80 = NULL, *vpd_pg83 = NULL;
>  	struct scsi_vpd *vpd_pg0 = NULL, *vpd_pg89 = NULL;
>  	unsigned long flags;
> +	struct module *mod;
> +	bool put_mod = false;
>  
>  	sdev = container_of(work, struct scsi_device, ew.work);
>  
> +	if (sdev->put_lld_mod_ref) {

Why do you need this flag at all?

Shouldn't you just always grab/release the module?  Why would you not
want to?

thanks,

greg k-h