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

John Hubbard
2020-05-22T04:15:13Z

This code was using get_user_pages*(), in a "Case 2" scenario
(DMA/RDMA), using the categorization from [1]. That means that it's
time to convert the get_user_pages*() + put_page() calls to
pin_user_pages*() + 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: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Gustavo A. R. Silva <gustavo@embeddedor.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-fbdev@vger.kernel.org
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
drivers/video/fbdev/pvr2fb.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/video/fbdev/pvr2fb.c b/drivers/video/fbdev/pvr2fb.c
index ceb6ef590597..2d9f69b93392 100644
--- a/drivers/video/fbdev/pvr2fb.c
+++ b/drivers/video/fbdev/pvr2fb.c
@@ -652,7 +652,7 @@ static ssize_t pvr2fb_write(struct fb_info *info, const char *buf,
if (!pages)
return -ENOMEM;

- ret = get_user_pages_fast((unsigned long)buf, nr_pages, FOLL_WRITE, pages);
+ ret = pin_user_pages_fast((unsigned long)buf, nr_pages, FOLL_WRITE, pages);
if (ret < nr_pages) {
if (ret < 0) {
/*
@@ -712,9 +712,7 @@ static ssize_t pvr2fb_write(struct fb_info *info, const char *buf,
ret = count;

out_unmap:
- for (i = 0; i < nr_pages; i++)
- put_page(pages[i]);
-
+ unpin_user_pages(pages, nr_pages);
kfree(pages);

return ret;
--
2.26.2