[PATCH 0/2] rapidio: convert to pin_user_pages(), plus a small fix

[PATCH 0/2] rapidio: convert to pin_user_pages(), plus a small fix

[John Hubbard]

While converting rapidio from get_user_pages() to pin_user_pages(),
I noticed a small problem in the error handling, so that is fixed
first. As such, the fix has -stable on CC, and can be separately
applied.

Note that I have only compile-tested these patches, although that does
also include cross-compiling for half a dozen arches.

John Hubbard (2):
  rapidio: fix an error in get_user_pages_fast() error handling
  rapidio: convert get_user_pages() --> pin_user_pages()

 drivers/rapidio/devices/rio_mport_cdev.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Alexandre Bounine <alex.bou9@gmail.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-media@vger.kernel.org

John Hubbard (2):
  rapidio: fix an error in get_user_pages_fast() error handling
  rapidio: convert get_user_pages() --> pin_user_pages()

 drivers/rapidio/devices/rio_mport_cdev.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)


base-commit: 5a9ffb954a3933d7867f4341684a23e008d6839b
-- 
2.26.2

[PATCH 1/2] rapidio: fix an error in get_user_pages_fast() error handling

[John Hubbard]

In the case of get_user_pages_fast() returning fewer pages than
requested, rio_dma_transfer() does not quite do the right thing.
It attempts to release all the pages that were requested, rather
than just the pages that were pinned.

Fix the error handling so that only the pages that were successfully
pinned are released.

Fixes: e8de370188d0 ("rapidio: add mport char device driver")
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Alexandre Bounine <alex.bou9@gmail.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-media@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/rapidio/devices/rio_mport_cdev.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c
index 8155f59ece38..10af330153b5 100644
--- a/drivers/rapidio/devices/rio_mport_cdev.c
+++ b/drivers/rapidio/devices/rio_mport_cdev.c
@@ -877,6 +877,11 @@ rio_dma_transfer(struct file *filp, u32 transfer_mode,
 				rmcd_error("pinned %ld out of %ld pages",
 					   pinned, nr_pages);
 			ret = -EFAULT;
+			/*
+			 * Set nr_pages up to mean "how many pages to unpin, in
+			 * the error handler:
+			 */
+			nr_pages = pinned;
 			goto err_pg;
 		}
 
-- 
2.26.2

Re: [PATCH 1/2] rapidio: fix an error in get_user_pages_fast() error handling

[Andrew Morton]

On Sun, 17 May 2020 16:56:19 -0700 John Hubbard <jhubbard@nvidia.com> wrote:

> In the case of get_user_pages_fast() returning fewer pages than
> requested, rio_dma_transfer() does not quite do the right thing.
> It attempts to release all the pages that were requested, rather
> than just the pages that were pinned.
> 
> Fix the error handling so that only the pages that were successfully
> pinned are released.
> 
> ...
>
> --- a/drivers/rapidio/devices/rio_mport_cdev.c
> +++ b/drivers/rapidio/devices/rio_mport_cdev.c
> @@ -877,6 +877,11 @@ rio_dma_transfer(struct file *filp, u32 transfer_mode,
>  				rmcd_error("pinned %ld out of %ld pages",
>  					   pinned, nr_pages);
>  			ret = -EFAULT;
> +			/*
> +			 * Set nr_pages up to mean "how many pages to unpin, in
> +			 * the error handler:
> +			 */
> +			nr_pages = pinned;
>  			goto err_pg;
>  		}

The code is a bit odd.  If (xfer->loc_addr == 0) then we do the `else'
stuff then fall through to

err_pg:
	if (!req->page_list) {
		for (i = 0; i < nr_pages; i++)
			put_page(page_list[i]);
		kfree(page_list);
	}

all of which is a big no-op because nr_pages==0 and page_list==NULL,
but it could all be easily avoided.

Oh well.  Reviewed-by:me.

[PATCH 2/2] rapidio: convert get_user_pages() --> pin_user_pages()

[John Hubbard]

This code was using get_user_pages_fast(), in a "Case 2" scenario
(DMA/RDMA), using the categorization from [1]. That means that it's
time to convert the get_user_pages_fast() + put_page() calls to
pin_user_pages_fast() + unpin_user_pages() calls.

There is some helpful background in [2]: basically, this is a small
part of fixing a long-standing disconnect between pinning pages, and
file systems' use of those pages.

[1] Documentation/core-api/pin_user_pages.rst

[2] "Explicit pinning of user-space pages":
    https://lwn.net/Articles/807108/

Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Alexandre Bounine <alex.bou9@gmail.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-media@vger.kernel.org
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/rapidio/devices/rio_mport_cdev.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c
index 10af330153b5..0ddd94d6f1e9 100644
--- a/drivers/rapidio/devices/rio_mport_cdev.c
+++ b/drivers/rapidio/devices/rio_mport_cdev.c
@@ -572,14 +572,12 @@ static void dma_req_free(struct kref *ref)
 	struct mport_dma_req *req = container_of(ref, struct mport_dma_req,
 			refcount);
 	struct mport_cdev_priv *priv = req->priv;
-	unsigned int i;
 
 	dma_unmap_sg(req->dmach->device->dev,
 		     req->sgt.sgl, req->sgt.nents, req->dir);
 	sg_free_table(&req->sgt);
 	if (req->page_list) {
-		for (i = 0; i < req->nr_pages; i++)
-			put_page(req->page_list[i]);
+		unpin_user_pages(req->page_list, req->nr_pages);
 		kfree(req->page_list);
 	}
 
@@ -815,7 +813,7 @@ rio_dma_transfer(struct file *filp, u32 transfer_mode,
 	struct mport_dma_req *req;
 	struct mport_dev *md = priv->md;
 	struct dma_chan *chan;
-	int i, ret;
+	int ret;
 	int nents;
 
 	if (xfer->length == 0)
@@ -862,7 +860,7 @@ rio_dma_transfer(struct file *filp, u32 transfer_mode,
 			goto err_req;
 		}
 
-		pinned = get_user_pages_fast(
+		pinned = pin_user_pages_fast(
 				(unsigned long)xfer->loc_addr & PAGE_MASK,
 				nr_pages,
 				dir == DMA_FROM_DEVICE ? FOLL_WRITE : 0,
@@ -870,7 +868,7 @@ rio_dma_transfer(struct file *filp, u32 transfer_mode,
 
 		if (pinned != nr_pages) {
 			if (pinned < 0) {
-				rmcd_error("get_user_pages_unlocked err=%ld",
+				rmcd_error("pin_user_pages_fast err=%ld",
 					   pinned);
 				nr_pages = 0;
 			} else
@@ -951,8 +949,7 @@ rio_dma_transfer(struct file *filp, u32 transfer_mode,
 
 err_pg:
 	if (!req->page_list) {
-		for (i = 0; i < nr_pages; i++)
-			put_page(page_list[i]);
+		unpin_user_pages(page_list, nr_pages);
 		kfree(page_list);
 	}
 err_req:
-- 
2.26.2