linux-kernel - [PATCH v2] orangefs: convert get_user_pages() --> pin_user

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Date:   Fri, 22 May 2020 20:59:09 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     LKML <linux-kernel@...r.kernel.org>
CC:     John Hubbard <jhubbard@...dia.com>,
        Mike Marshall <hubcap@...ibond.com>,
        Martin Brandenburg <martin@...ibond.com>,
        <devel@...ts.orangefs.org>, <linux-fsdevel@...r.kernel.org>
Subject: [PATCH v2] orangefs: convert get_user_pages() --> pin_user_pages()

This code was using get_user_pages*(), in a "Case 1" scenario
(Direct IO), 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: Mike Marshall <hubcap@...ibond.com>
Cc: Martin Brandenburg <martin@...ibond.com>
Cc: devel@...ts.orangefs.org
Cc: linux-fsdevel@...r.kernel.org
Signed-off-by: John Hubbard <jhubbard@...dia.com>
---

Hi,

Note that I have only compile-tested this patch, although that does
also include cross-compiling for a few other arches.

Changes since v1 [3]: correct the commit description, so that
it refers to "Case 1" instead of "Case 2".


[3] https://lore.kernel.org/r/20200518060139.2828423-1-jhubbard@nvidia.com

thanks,
John Hubbard
NVIDIA

 fs/orangefs/orangefs-bufmap.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/fs/orangefs/orangefs-bufmap.c b/fs/orangefs/orangefs-bufmap.c
index 2bb916d68576..538e839590ef 100644
--- a/fs/orangefs/orangefs-bufmap.c
+++ b/fs/orangefs/orangefs-bufmap.c
@@ -168,10 +168,7 @@ static DEFINE_SPINLOCK(orangefs_bufmap_lock);
 static void
 orangefs_bufmap_unmap(struct orangefs_bufmap *bufmap)
 {
-	int i;
-
-	for (i = 0; i < bufmap->page_count; i++)
-		put_page(bufmap->page_array[i]);
+	unpin_user_pages(bufmap->page_array, bufmap->page_count);
 }
 
 static void
@@ -268,7 +265,7 @@ orangefs_bufmap_map(struct orangefs_bufmap *bufmap,
 	int offset = 0, ret, i;
 
 	/* map the pages */
-	ret = get_user_pages_fast((unsigned long)user_desc->ptr,
+	ret = pin_user_pages_fast((unsigned long)user_desc->ptr,
 			     bufmap->page_count, FOLL_WRITE, bufmap->page_array);
 
 	if (ret < 0)
@@ -280,7 +277,7 @@ orangefs_bufmap_map(struct orangefs_bufmap *bufmap,
 
 		for (i = 0; i < ret; i++) {
 			SetPageError(bufmap->page_array[i]);
-			put_page(bufmap->page_array[i]);
+			unpin_user_page(bufmap->page_array[i]);
 		}
 		return -ENOMEM;
 	}
-- 
2.26.2