From: "Aneesh Kumar K.V" <aneesh.ku...@linux.vnet.ibm.com>
GCC is very likely to read the pagetables just once and cache them in
the local stack or in a register, but it is can also decide to re-read
the pagetables. The problem is that the pagetable in those places can
change from under gcc.
With THP/hugetlbfs the pmd (and pgd for hugetlbfs giga pages) can
change under gup_fast. The pages won't be freed untill we finish
gup fast because we have irq disabled and we free these pages via
rcu callback.
Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com>
---
arch/powerpc/mm/gup.c | 8 ++++----
arch/powerpc/mm/hugetlbpage.c | 2 +-
2 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/mm/gup.c b/arch/powerpc/mm/gup.c
index 3d36fd7..4823e4d 100644
--- a/arch/powerpc/mm/gup.c
+++ b/arch/powerpc/mm/gup.c
@@ -34,7 +34,7 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long
addr,
ptep = pte_offset_kernel(&pmd, addr);
do {
- pte_t pte = *ptep;
+ pte_t pte = ACCESS_ONCE(*ptep);
struct page *page;
if ((pte_val(pte) & mask) != result)
@@ -63,7 +63,7 @@ static int gup_pmd_range(pud_t pud, unsigned long addr,
unsigned long end,
pmdp = pmd_offset(&pud, addr);
do {
- pmd_t pmd = *pmdp;
+ pmd_t pmd = ACCESS_ONCE(*pmdp);
next = pmd_addr_end(addr, end);
/*
@@ -102,7 +102,7 @@ static int gup_pud_range(pgd_t pgd, unsigned long addr,
unsigned long end,
pudp = pud_offset(&pgd, addr);
do {
- pud_t pud = *pudp;
+ pud_t pud = ACCESS_ONCE(*pudp);
next = pud_addr_end(addr, end);
if (pud_none(pud))
@@ -165,7 +165,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
int write,
pgdp = pgd_offset(mm, addr);
do {
- pgd_t pgd = *pgdp;
+ pgd_t pgd = ACCESS_ONCE(*pgdp);
pr_devel(" %016lx: normal pgd %p\n", addr,
(void *)pgd_val(pgd));
diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index e9e6882..f2f01fd 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -1024,7 +1024,7 @@ int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned
long addr,
if (pte_end < end)
end = pte_end;
- pte = *ptep;
+ pte = ACCESS_ONCE(*ptep);
mask = _PAGE_PRESENT | _PAGE_USER;
if (write)
mask |= _PAGE_RW;
--
1.8.1.2
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