[PATCH v2 02/14] mm/gup: Cache p4d in follow_p4d_mask()

peterx
2024-03-18T20:04:12Z

Add a variable to cache p4d in follow_p4d_mask(). It's a good practise to
make sure all the following checks will have a consistent view of the entry.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
mm/gup.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index df83182ec72d..69a777f4fc5c 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -772,16 +772,17 @@ static struct page *follow_p4d_mask(struct vm_area_struct *vma,
unsigned int flags,
struct follow_page_context *ctx)
{
- p4d_t *p4d;
+ p4d_t *p4dp, p4d;

- p4d = p4d_offset(pgdp, address);
- if (p4d_none(*p4d))
+ p4dp = p4d_offset(pgdp, address);
+ p4d = READ_ONCE(*p4dp);
+ if (p4d_none(p4d))
return no_page_table(vma, flags);
- BUILD_BUG_ON(p4d_huge(*p4d));
- if (unlikely(p4d_bad(*p4d)))
+ BUILD_BUG_ON(p4d_huge(p4d));
+ if (unlikely(p4d_bad(p4d)))
return no_page_table(vma, flags);

- return follow_pud_mask(vma, address, p4d, flags, ctx);
+ return follow_pud_mask(vma, address, p4dp, flags, ctx);
}

/**
--
2.44.0