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@xxxxxxx> Cc: Steve Capper <steve.capper@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx> --- Hi Andrew, Please update the patch in your queue with this version. It fixes the ltp failures reported by Yury[0]. The original patch led to incorrect ref-count on certain pages due to taking a referencing on the following page in some instances. Should be fixed with this version. Thanks, Punit [0] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-June/510318.html mm/gup.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index e74e0b5a0c7c..6bd39264d0e7 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1354,8 +1354,7 @@ 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)++; @@ -1363,6 +1362,7 @@ 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; @@ -1392,8 +1392,7 @@ 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)++; @@ -1401,6 +1400,7 @@ 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; @@ -1429,8 +1429,7 @@ 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)++; @@ -1438,6 +1437,7 @@ 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; -- 2.11.0
