Re: [PATCH V2] scsi: core: put LLD module refcnt after SCSI device is released

[Ming Lei <ming.lei@redhat.com>]

On Thu, Sep 30, 2021 at 03:40:26PM +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 put LLD module refcnt after SCSI device is released.
> 
> The real release handler can be run from wq context in case of
> in_interrupt(), so add one atomic counter for serializing putting
> module via current and wq context. This way is fine since we don't
> call scsi_device_put() in fast IO path.
> 
> 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        |  8 +++++++-
>  drivers/scsi/scsi_sysfs.c  | 10 ++++++++++
>  include/scsi/scsi_device.h |  2 ++
>  3 files changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index b241f9e3885c..b6612161587f 100644
> --- a/drivers/scsi/scsi.c
> +++ b/drivers/scsi/scsi.c
> @@ -553,8 +553,14 @@ 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;
> +
> +	atomic_inc(&sdev->put_dev_cnt);
> +
>  	put_device(&sdev->sdev_gendev);
> +
> +	if (atomic_dec_if_positive(&sdev->put_dev_cnt) >= 0)
> +		module_put(mod);

oops, sdev can be freed now, so this approach isn't good too, :-(

Will think further about the solution.

thanks,
Ming