mm, gup: ensure real head page is ref-counted when using hugepages

commit d63206ee32b6e64b0e12d46e5d6004afd9913713 upstream.

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.

[punit.agrawal@arm.com: fix arm64 ltp failure]
Link: http://lkml.kernel.org/r/20170619170145.25577-5-punit.agrawal@arm.com
Link: http://lkml.kernel.org/r/20170522133604.11392-3-punit.agrawal@arm.com
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>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/gup.c b/mm/gup.c
index a09076ec31680e1f84041cebfc000649e776f561..a736aef408233ecc61e1959725a5b61f663e8873 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1313,8 +1313,7 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
                return 0;
 
        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)++;
@@ -1322,6 +1321,7 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
                refs++;
        } while (addr += PAGE_SIZE, addr != end);
 
+       head = compound_head(pmd_page(orig));
        if (!page_cache_add_speculative(head, refs)) {
                *nr -= refs;
                return 0;
@@ -1347,8 +1347,7 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
                return 0;
 
        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)++;
@@ -1356,6 +1355,7 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
                refs++;
        } while (addr += PAGE_SIZE, addr != end);
 
+       head = compound_head(pud_page(orig));
        if (!page_cache_add_speculative(head, refs)) {
                *nr -= refs;
                return 0;
@@ -1382,8 +1382,7 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
                return 0;
 
        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)++;
@@ -1391,6 +1390,7 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
                refs++;
        } while (addr += PAGE_SIZE, addr != end);
 
+       head = compound_head(pgd_page(orig));
        if (!page_cache_add_speculative(head, refs)) {
                *nr -= refs;
                return 0;