Re: [PATCH 07/12] vhost-scsi: convert put_page() to put_user_page*()

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jul 23, 2019 at 09:25:13PM -0700, john.hubbard@gmail.com wrote:
> From: Jérôme Glisse <jglisse@redhat.com>
> 
> For pages that were retained via get_user_pages*(), release those pages
> via the new put_user_page*() routines, instead of via put_page().
> 
> This is part a tree-wide conversion, as described in commit fc1d8e7cca2d
> ("mm: introduce put_user_page*(), placeholder versions").
> 
> Changes from Jérôme's original patch:
> 
> * Changed a WARN_ON to a BUG_ON.
> 
> Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> Cc: virtualization@lists.linux-foundation.org
> Cc: linux-fsdevel@vger.kernel.org
> Cc: linux-block@vger.kernel.org
> Cc: linux-mm@kvack.org
> Cc: Jan Kara <jack@suse.cz>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Johannes Thumshirn <jthumshirn@suse.de>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Boaz Harrosh <boaz@plexistor.com>
> Cc: Miklos Szeredi <miklos@szeredi.hu>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  drivers/vhost/scsi.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> index a9caf1bc3c3e..282565ab5e3f 100644
> --- a/drivers/vhost/scsi.c
> +++ b/drivers/vhost/scsi.c
> @@ -329,11 +329,11 @@ static void vhost_scsi_release_cmd(struct se_cmd *se_cmd)
>  
>  	if (tv_cmd->tvc_sgl_count) {
>  		for (i = 0; i < tv_cmd->tvc_sgl_count; i++)
> -			put_page(sg_page(&tv_cmd->tvc_sgl[i]));
> +			put_user_page(sg_page(&tv_cmd->tvc_sgl[i]));
>  	}
>  	if (tv_cmd->tvc_prot_sgl_count) {
>  		for (i = 0; i < tv_cmd->tvc_prot_sgl_count; i++)
> -			put_page(sg_page(&tv_cmd->tvc_prot_sgl[i]));
> +			put_user_page(sg_page(&tv_cmd->tvc_prot_sgl[i]));
>  	}
>  
>  	vhost_scsi_put_inflight(tv_cmd->inflight);
> @@ -630,6 +630,13 @@ vhost_scsi_map_to_sgl(struct vhost_scsi_cmd *cmd,
>  	size_t offset;
>  	unsigned int npages = 0;
>  
> +	/*
> +	 * Here in all cases we should have an IOVEC which use GUP. If that is
> +	 * not the case then we will wrongly call put_user_page() and the page
> +	 * refcount will go wrong (this is in vhost_scsi_release_cmd())
> +	 */
> +	WARN_ON(!iov_iter_get_pages_use_gup(iter));
> +
>  	bytes = iov_iter_get_pages(iter, pages, LONG_MAX,
>  				VHOST_SCSI_PREALLOC_UPAGES, &offset);
>  	/* No pages were pinned */
> @@ -681,7 +688,7 @@ vhost_scsi_iov_to_sgl(struct vhost_scsi_cmd *cmd, bool write,
>  			while (p < sg) {
>  				struct page *page = sg_page(p++);
>  				if (page)
> -					put_page(page);
> +					put_user_page(page);
>  			}
>  			return ret;
>  		}
> -- 
> 2.22.0