From: John Hubbard <jhubbard@nvidia.com>
To: LKML <linux-kernel@vger.kernel.org>
Cc: "John Hubbard" <jhubbard@nvidia.com>,
"Kai Mäkisara" <Kai.Makisara@kolumbus.fi>,
"James E . J . Bottomley" <jejb@linux.ibm.com>,
"Martin K . Petersen" <martin.petersen@oracle.com>,
linux-scsi@vger.kernel.org
Subject: [PATCH] scsi: st: convert convert get_user_pages() --> pin_user_pages()
Date: Mon, 18 May 2020 21:55:25 -0700 [thread overview]
Message-ID: <20200519045525.2446851-1-jhubbard@nvidia.com> (raw)
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.
Note that this effectively changes the code's behavior as well: it now
ultimately calls set_page_dirty_lock(), instead of SetPageDirty().This
is probably more accurate.
As Christoph Hellwig put it, "set_page_dirty() is only safe if we are
dealing with a file backed page where we have reference on the inode it
hangs off." [3]
Also, this deletes one of the two FIXME comments (about refcounting),
because there is nothing wrong with the refcounting at this point.
[1] Documentation/core-api/pin_user_pages.rst
[2] "Explicit pinning of user-space pages":
https://lwn.net/Articles/807108/
[3] https://lore.kernel.org/r/20190723153640.GB720@lst.de
Cc: "Kai Mäkisara" <Kai.Makisara@kolumbus.fi>
Cc: James E.J. Bottomley <jejb@linux.ibm.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: linux-scsi@vger.kernel.org
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
drivers/scsi/st.c | 19 +++++--------------
1 file changed, 5 insertions(+), 14 deletions(-)
diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index c5f9b348b438..0369c7edfd94 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -4922,7 +4922,7 @@ static int sgl_map_user_pages(struct st_buffer *STbp,
unsigned long end = (uaddr + count + PAGE_SIZE - 1) >> PAGE_SHIFT;
unsigned long start = uaddr >> PAGE_SHIFT;
const int nr_pages = end - start;
- int res, i, j;
+ int res, i;
struct page **pages;
struct rq_map_data *mdata = &STbp->map_data;
@@ -4944,7 +4944,7 @@ static int sgl_map_user_pages(struct st_buffer *STbp,
/* Try to fault in all of the necessary pages */
/* rw==READ means read from drive, write into memory area */
- res = get_user_pages_fast(uaddr, nr_pages, rw == READ ? FOLL_WRITE : 0,
+ res = pin_user_pages_fast(uaddr, nr_pages, rw == READ ? FOLL_WRITE : 0,
pages);
/* Errors and no page mapped should return here */
@@ -4964,8 +4964,7 @@ static int sgl_map_user_pages(struct st_buffer *STbp,
return nr_pages;
out_unmap:
if (res > 0) {
- for (j=0; j < res; j++)
- put_page(pages[j]);
+ unpin_user_pages(pages, res);
res = 0;
}
kfree(pages);
@@ -4977,18 +4976,10 @@ static int sgl_map_user_pages(struct st_buffer *STbp,
static int sgl_unmap_user_pages(struct st_buffer *STbp,
const unsigned int nr_pages, int dirtied)
{
- int i;
+ /* FIXME: cache flush missing for rw==READ */
- for (i=0; i < nr_pages; i++) {
- struct page *page = STbp->mapped_pages[i];
+ unpin_user_pages_dirty_lock(STbp->mapped_pages, nr_pages, dirtied);
- if (dirtied)
- SetPageDirty(page);
- /* FIXME: cache flush missing for rw==READ
- * FIXME: call the correct reference counting function
- */
- put_page(page);
- }
kfree(STbp->mapped_pages);
STbp->mapped_pages = NULL;
--
2.26.2
next reply other threads:[~2020-05-19 4:55 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-19 4:55 John Hubbard [this message]
2020-05-19 20:12 ` [PATCH] scsi: st: convert convert get_user_pages() --> pin_user_pages() John Hubbard
2020-05-20 1:57 ` Martin K. Petersen
2020-05-21 19:47 ` Bart Van Assche
2020-05-21 19:57 ` John Hubbard
2020-05-21 20:58 ` Bart Van Assche
2020-05-22 8:32 ` "Kai Mäkisara (Kolumbus)"
2020-05-26 18:15 ` John Hubbard
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