From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f71.google.com (mail-oi0-f71.google.com [209.85.218.71]) by kanga.kvack.org (Postfix) with ESMTP id 0A0756B02C3 for ; Mon, 5 Jun 2017 08:51:58 -0400 (EDT) Received: by mail-oi0-f71.google.com with SMTP id e1so84856573oig.12 for ; Mon, 05 Jun 2017 05:51:58 -0700 (PDT) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id t198si2361282oie.29.2017.06.05.05.51.56 for ; Mon, 05 Jun 2017 05:51:57 -0700 (PDT) From: Punit Agrawal Subject: [PATCH v4.1 4/8] mm, gup: Ensure real head page is ref-counted when using hugepages Date: Mon, 5 Jun 2017 13:51:12 +0100 Message-Id: <20170605125112.19530-1-punit.agrawal@arm.com> In-Reply-To: <20170524115409.31309-5-punit.agrawal@arm.com> References: <20170524115409.31309-5-punit.agrawal@arm.com> Sender: owner-linux-mm@kvack.org List-ID: To: akpm@linux-foundation.org Cc: Punit Agrawal , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will.deacon@arm.com, n-horiguchi@ah.jp.nec.com, kirill.shutemov@linux.intel.com, mike.kravetz@oracle.com, steve.capper@arm.com, mark.rutland@arm.com, linux-arch@vger.kernel.org, aneesh.kumar@linux.vnet.ibm.com, ynorov@caviumnetworks.com, Michal Hocko 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 Cc: Steve Capper Cc: Michal Hocko Cc: "Kirill A. Shutemov" Cc: Aneesh Kumar K.V --- 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org