linux-kernel - [PATCH] mm/gup: further simplify __gup_device

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Date:   Fri, 3 Sep 2021 17:42:24 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     LKML <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        John Hubbard <jhubbard@...dia.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Miaohe Lin" <linmiaohe@...wei.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        "Jan Kara" <jack@...e.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH] mm/gup: further simplify __gup_device_huge()

commit 6401c4eb57f9 ("mm: gup: fix potential pgmap refcnt leak in
__gup_device_huge()") simplified the return paths, but didn't go quite
far enough, as discussed in [1].

Remove the "ret" variable entirely, because there is enough information
already available to provide the return value.

[1] https://lore.kernel.org/r/CAHk-=wgQTRX=5SkCmS+zfmpqubGHGJvXX_HgnPG8JSpHKHBMeg@mail.gmail.com

Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Miaohe Lin <linmiaohe@...wei.com>
Cc: Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc: Jan Kara <jack@...e.cz>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Signed-off-by: John Hubbard <jhubbard@...dia.com>
---
 mm/gup.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 9935a4480710..6e62f1518c1f 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2241,7 +2241,6 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
 {
 	int nr_start = *nr;
 	struct dev_pagemap *pgmap = NULL;
-	int ret = 1;
 
 	do {
 		struct page *page = pfn_to_page(pfn);
@@ -2249,14 +2248,12 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
 		pgmap = get_dev_pagemap(pfn, pgmap);
 		if (unlikely(!pgmap)) {
 			undo_dev_pagemap(nr, nr_start, flags, pages);
-			ret = 0;
 			break;
 		}
 		SetPageReferenced(page);
 		pages[*nr] = page;
 		if (unlikely(!try_grab_page(page, flags))) {
 			undo_dev_pagemap(nr, nr_start, flags, pages);
-			ret = 0;
 			break;
 		}
 		(*nr)++;
@@ -2264,7 +2261,7 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
 	} while (addr += PAGE_SIZE, addr != end);
 
 	put_dev_pagemap(pgmap);
-	return ret;
+	return addr == end;
 }
 
 static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
-- 
2.33.0