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15 Aug 2022 00:40:29 -0700 X-IronPort-AV: E=Sophos;i="5.93,237,1654585200"; d="scan'208";a="582796154" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by orsmga006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Aug 2022 00:40:26 -0700 From: "Huang, Ying" To: Haiyue Wang Cc: , , , , , , , , Subject: Re: [PATCH v5 1/2] mm: migration: fix the FOLL_GET failure on following huge page References: <20220812084921.409142-1-haiyue.wang@intel.com> <20220815070240.470469-1-haiyue.wang@intel.com> <20220815070240.470469-2-haiyue.wang@intel.com> Date: Mon, 15 Aug 2022 15:40:17 +0800 In-Reply-To: <20220815070240.470469-2-haiyue.wang@intel.com> (Haiyue Wang's message of "Mon, 15 Aug 2022 15:02:39 +0800") Message-ID: <87k07ac5um.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660549231; 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dmarc=pass (policy=none) header.from=intel.com X-Stat-Signature: ibu98mt4cq5expgwmzd1wpj5qdg9m59y X-Rspamd-Queue-Id: 424561A0181 Authentication-Results: imf19.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=GVNonQMg; spf=pass (imf19.hostedemail.com: domain of ying.huang@intel.com designates 192.55.52.115 as permitted sender) smtp.mailfrom=ying.huang@intel.com; dmarc=pass (policy=none) header.from=intel.com X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1660549231-301768 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Haiyue Wang writes: > Not all huge page APIs support FOLL_GET option, so move_pages() syscall > will fail to get the page node information for some huge pages. > > Like x86 on linux 5.19 with 1GB huge page API follow_huge_pud(), it will > return NULL page for FOLL_GET when calling move_pages() syscall with the > NULL 'nodes' parameter, the 'status' parameter has '-2' error in array. > > Note: follow_huge_pud() now supports FOLL_GET in linux 6.0. > Link: https://lore.kernel.org/all/20220714042420.1847125-3-naoya.horiguchi@linux.dev > > But these huge page APIs don't support FOLL_GET: > 1. follow_huge_pud() in arch/s390/mm/hugetlbpage.c > 2. follow_huge_addr() in arch/ia64/mm/hugetlbpage.c > It will cause WARN_ON_ONCE for FOLL_GET. > 3. follow_huge_pgd() in mm/hugetlb.c > > This is an temporary solution to mitigate the side effect of the race > condition fix by calling follow_page() with FOLL_GET set for huge pages. > > After supporting follow huge page by FOLL_GET is done, this fix can be > reverted safely. > > Fixes: 4cd614841c06 ("mm: migration: fix possible do_pages_stat_array racing with memory offline") > Signed-off-by: Haiyue Wang LGTM, Thanks! Reviewed-by: "Huang, Ying" > --- > mm/migrate.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 6a1597c92261..581dfaad9257 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1848,6 +1848,7 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, > > for (i = 0; i < nr_pages; i++) { > unsigned long addr = (unsigned long)(*pages); > + unsigned int foll_flags = FOLL_DUMP; > struct vm_area_struct *vma; > struct page *page; > int err = -EFAULT; > @@ -1856,8 +1857,12 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, > if (!vma) > goto set_status; > > + /* Not all huge page follow APIs support 'FOLL_GET' */ > + if (!is_vm_hugetlb_page(vma)) > + foll_flags |= FOLL_GET; > + > /* FOLL_DUMP to ignore special (like zero) pages */ > - page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); > + page = follow_page(vma, addr, foll_flags); > > err = PTR_ERR(page); > if (IS_ERR(page)) > @@ -1865,7 +1870,8 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, > > if (page && !is_zone_device_page(page)) { > err = page_to_nid(page); > - put_page(page); > + if (foll_flags & FOLL_GET) > + put_page(page); > } else { > err = -ENOENT; > }