Re: [PATCH 3/3] scsi: proper state checking and module refcount handling in scsi_device_get

[James Bottomley <jbottomley@parallels.com>]

On Thu, 2015-01-29 at 00:00 +0100, Christoph Hellwig wrote:
> This effectively reverts commits 85b6c7 ("[SCSI] sd: fix cache flushing on
> module removal (and individual device removal)" and dc4515ea ("scsi: always
> increment reference count").
> 
> We now never call scsi_device_get from the shutdown path, and the fact
> that we started grabbing reference there in commit 85b6c7 turned out
> turned out to create more problems than it solves, and required
> workarounds for workarounds for workarounds. Move back to properly checking
> the device state and carefully handle module refcounting.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/scsi/scsi.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index 9b38299..95f0293 100644
> --- a/drivers/scsi/scsi.c
> +++ b/drivers/scsi/scsi.c
> @@ -982,15 +982,18 @@ EXPORT_SYMBOL(scsi_report_opcode);
>   */
>  int scsi_device_get(struct scsi_device *sdev)
>  {
> -	if (sdev->sdev_state == SDEV_DEL)
> -		return -ENXIO;
> +	if (sdev->sdev_state == SDEV_DEL || sdev->sdev_state == SDEV_CANCEL)
> +		goto fail;
>  	if (!get_device(&sdev->sdev_gendev))
> -		return -ENXIO;
> -	/* We can fail try_module_get if we're doing SCSI operations
> -	 * from module exit (like cache flush) */
> -	__module_get(sdev->host->hostt->module);
> -
> +		goto fail;
> +	if (!try_module_get(sdev->host->hostt->module))
> +		goto fail_put_device;
>  	return 0;
> +
> +fail_put_device:
> +	put_device(&sdev->sdev_gendev);
> +fail:
> +	return -ENXIO;
>  }
>  EXPORT_SYMBOL(scsi_device_get);

If we can get away with this, I'm all for this approach.  However, you
need to document in a comment or above the function that it may not be
called in module exit functions and why.

Other than the comment issue, the series looks good,

Thanks,

James