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Subject[PATCH] mm: gup: Re-define follow_page_mask output parameter page_mask usage
Date
From: Chen Gang <chengang@emindsoft.com.cn>

For a pure output parameter:

- When callee fails, the caller should not assume the output parameter
is still valid.

- And callee should not assume the pure output parameter must be
provided by caller -- caller has right to pass NULL when caller does
not care about it.

Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
---
include/linux/mm.h | 5 ++---
mm/gup.c | 6 +++---
mm/mlock.c | 2 +-
mm/nommu.c | 1 -
4 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b21e5f3..5c560fd 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2205,10 +2205,9 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
unsigned int *page_mask);

static inline struct page *follow_page(struct vm_area_struct *vma,
- unsigned long address, unsigned int foll_flags)
+ unsigned long address, unsigned int foll_flags)
{
- unsigned int unused_page_mask;
- return follow_page_mask(vma, address, foll_flags, &unused_page_mask);
+ return follow_page_mask(vma, address, foll_flags, NULL);
}

#define FOLL_WRITE 0x01 /* check pte is writable */
diff --git a/mm/gup.c b/mm/gup.c
index 96b2b2f..9684b06 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -222,8 +222,6 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
struct page *page;
struct mm_struct *mm = vma->vm_mm;

- *page_mask = 0;
-
page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
if (!IS_ERR(page)) {
BUG_ON(flags & FOLL_GET);
@@ -298,7 +296,8 @@ struct page *follow_page_mask(struct vm_area_struct *vma,

page = follow_trans_huge_pmd(vma, address, pmd, flags);
spin_unlock(ptl);
- *page_mask = HPAGE_PMD_NR - 1;
+ if (page_mask)
+ *page_mask = HPAGE_PMD_NR - 1;
return page;
}

@@ -574,6 +573,7 @@ retry:
if (unlikely(fatal_signal_pending(current)))
return i ? i : -ERESTARTSYS;
cond_resched();
+ page_mask = 0;
page = follow_page_mask(vma, start, foll_flags, &page_mask);
if (!page) {
int ret;
diff --git a/mm/mlock.c b/mm/mlock.c
index ef8dc9f..626eb58 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -438,7 +438,7 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,

while (start < end) {
struct page *page;
- unsigned int page_mask;
+ unsigned int page_mask = 0;
unsigned long page_increm;
struct pagevec pvec;
struct zone *zone;
diff --git a/mm/nommu.c b/mm/nommu.c
index 95daf81..c1a0a89 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1749,7 +1749,6 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
unsigned long address, unsigned int flags,
unsigned int *page_mask)
{
- *page_mask = 0;
return NULL;
}

--
1.9.3
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