diff mbox

[v4,4/8] mm, gup: Ensure real head page is ref-counted when using hugepages

Message ID 20170524115409.31309-5-punit.agrawal@arm.com (mailing list archive)
State New, archived
Headers show

Commit Message

Punit Agrawal May 24, 2017, 11:54 a.m. UTC 
When speculatively taking references to a hugepage using
page_cache_add_speculative() in gup_huge_pmd(), it is assumed that the
page returned by pmd_page() is the head page. Although normally true,
this assumption doesn't hold when the hugepage comprises of successive
page table entries such as when using contiguous bit on arm64 at PTE or
PMD levels.

This can be addressed by ensuring that the page passed to
page_cache_add_speculative() is the real head or by de-referencing the
head page within the function.

We take the first approach to keep the usage pattern aligned with
page_cache_get_speculative() where users already pass the appropriate
page, i.e., the de-referenced head.

Apply the same logic to fix gup_huge_[pud|pgd]() as well.

Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Acked-by: Steve Capper <steve.capper@arm.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 mm/gup.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)
diff mbox

Patch

diff --git a/mm/gup.c b/mm/gup.c
index ccf8cb38234f..be67996513be 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1358,8 +1358,7 @@  static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 		return __gup_device_huge_pmd(orig, addr, end, pages, nr);
 
 	refs = 0;
-	head = pmd_page(orig);
-	page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
+	page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
 	do {
 		pages[*nr] = page;
 		(*nr)++;
@@ -1367,6 +1366,7 @@  static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 		refs++;
 	} while (addr += PAGE_SIZE, addr != end);
 
+	head = compound_head(page);
 	if (!page_cache_add_speculative(head, refs)) {
 		*nr -= refs;
 		return 0;
@@ -1396,8 +1396,7 @@  static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
 		return __gup_device_huge_pud(orig, addr, end, pages, nr);
 
 	refs = 0;
-	head = pud_page(orig);
-	page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
+	page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
 	do {
 		pages[*nr] = page;
 		(*nr)++;
@@ -1405,6 +1404,7 @@  static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
 		refs++;
 	} while (addr += PAGE_SIZE, addr != end);
 
+	head = compound_head(page);
 	if (!page_cache_add_speculative(head, refs)) {
 		*nr -= refs;
 		return 0;
@@ -1433,8 +1433,7 @@  static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
 
 	BUILD_BUG_ON(pgd_devmap(orig));
 	refs = 0;
-	head = pgd_page(orig);
-	page = head + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
+	page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
 	do {
 		pages[*nr] = page;
 		(*nr)++;
@@ -1442,6 +1441,7 @@  static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
 		refs++;
 	} while (addr += PAGE_SIZE, addr != end);
 
+	head = compound_head(page);
 	if (!page_cache_add_speculative(head, refs)) {
 		*nr -= refs;
 		return 0;