linux-kernel - [PATCH v2 2/2] mm/gup: fix a misnamed "write" argument, and a related bug

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Message-ID: <20191014184639.1512873-3-jhubbard@nvidia.com>
Date:   Mon, 14 Oct 2019 11:46:39 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     Christoph Hellwig <hch@...radead.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Keith Busch <keith.busch@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        LKML <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        John Hubbard <jhubbard@...dia.com>,
        kbuild test robot <lkp@...el.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Christoph Hellwig <hch@....de>
Subject: [PATCH v2 2/2] mm/gup: fix a misnamed "write" argument, and a related bug

In several routines, the "flags" argument is incorrectly
named "write". Change it to "flags".

Also, in one place, the misnaming led to an actual bug:
"flags & FOLL_WRITE" is required, rather than just "flags".
(That problem was flagged by krobot, in v1 of this patch.)

Also, change the flags argument from int, to unsigned int.

You can see that this was a simple oversight, because the
calling code passes "flags" to the fifth argument:

gup_pgd_range():
    ...
    if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr,
		    PGDIR_SHIFT, next, flags, pages, nr))

...which, until this patch, the callees referred to as "write".

Also, change two lines to avoid checkpatch line length
complaints, and another line to fix another oversight
that checkpatch called out: missing "int" on pdshift.

Fixes: b798bec4741b ("mm/gup: change write parameter to flags in fast walk")
Reported-by: kbuild test robot <lkp@...el.com>
Suggested-by: Kirill A. Shutemov <kirill@...temov.name>
Suggested-by: Ira Weiny <ira.weiny@...el.com>
Cc: Christoph Hellwig <hch@....de>
Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
Signed-off-by: John Hubbard <jhubbard@...dia.com>
---
 mm/gup.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 23a9f9c9d377..8f236a335ae9 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1973,7 +1973,8 @@ static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end,
 }
 
 static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
-		       unsigned long end, int write, struct page **pages, int *nr)
+		       unsigned long end, unsigned int flags,
+		       struct page **pages, int *nr)
 {
 	unsigned long pte_end;
 	struct page *head, *page;
@@ -1986,7 +1987,7 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
 
 	pte = READ_ONCE(*ptep);
 
-	if (!pte_access_permitted(pte, write))
+	if (!pte_access_permitted(pte, flags & FOLL_WRITE))
 		return 0;
 
 	/* hugepages are never "special" */
@@ -2023,7 +2024,7 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
 }
 
 static int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
-		unsigned int pdshift, unsigned long end, int write,
+		unsigned int pdshift, unsigned long end, unsigned int flags,
 		struct page **pages, int *nr)
 {
 	pte_t *ptep;
@@ -2033,7 +2034,7 @@ static int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
 	ptep = hugepte_offset(hugepd, addr, pdshift);
 	do {
 		next = hugepte_addr_end(addr, end, sz);
-		if (!gup_hugepte(ptep, sz, addr, end, write, pages, nr))
+		if (!gup_hugepte(ptep, sz, addr, end, flags, pages, nr))
 			return 0;
 	} while (ptep++, addr = next, addr != end);
 
@@ -2041,7 +2042,7 @@ static int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
 }
 #else
 static inline int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
-		unsigned pdshift, unsigned long end, int write,
+		unsigned int pdshift, unsigned long end, unsigned int flags,
 		struct page **pages, int *nr)
 {
 	return 0;
@@ -2049,7 +2050,8 @@ static inline int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
 #endif /* CONFIG_ARCH_HAS_HUGEPD */
 
 static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
-		unsigned long end, unsigned int flags, struct page **pages, int *nr)
+			unsigned long end, unsigned int flags,
+			struct page **pages, int *nr)
 {
 	struct page *head, *page;
 	int refs;
-- 
2.23.0