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Tue, 16 Aug 2022 08:54:48 +0000 (UTC) X-FDA: 79804845456.02.4F9EA2F Received: from out30-42.freemail.mail.aliyun.com (out30-42.freemail.mail.aliyun.com [115.124.30.42]) by imf15.hostedemail.com (Postfix) with ESMTP id 7056FA01C7 for ; Tue, 16 Aug 2022 08:54:46 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R661e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046051;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=11;SR=0;TI=SMTPD_---0VMPKNX3_1660640081; Received: from 30.97.48.47(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0VMPKNX3_1660640081) by smtp.aliyun-inc.com; Tue, 16 Aug 2022 16:54:41 +0800 Message-ID: Date: Tue, 16 Aug 2022 16:54:53 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [PATCH v6 1/2] mm: migration: fix the FOLL_GET failure on following huge page To: Haiyue Wang , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, david@redhat.com, apopple@nvidia.com, linmiaohe@huawei.com, ying.huang@intel.com, songmuchun@bytedance.com, naoya.horiguchi@linux.dev, alex.sierra@amd.com References: <20220812084921.409142-1-haiyue.wang@intel.com> <20220816022102.582865-1-haiyue.wang@intel.com> <20220816022102.582865-2-haiyue.wang@intel.com> From: Baolin Wang In-Reply-To: <20220816022102.582865-2-haiyue.wang@intel.com> Content-Type: text/plain; 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b=G47DACHJA2dTUjJd9mmT1g/1WTZ/1+LkClvKiZWYMwEopDjkvX1yHoyEjF9LJ2poanLu8I yQMQUKdImx6cfZ80O9gWCbWoQYJvtNLX+FCLoYdzwqe80Qb8NnJ1TLjixEVFHnbacYn4/I +K1rLUKz3TUUpXXuyM+aGG79rej5VkE= Authentication-Results: imf15.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=alibaba.com; spf=pass (imf15.hostedemail.com: domain of baolin.wang@linux.alibaba.com designates 115.124.30.42 as permitted sender) smtp.mailfrom=baolin.wang@linux.alibaba.com X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 7056FA01C7 X-Stat-Signature: 5xk9sm6u1npfexqftccogem4snpq1pwn X-Rspam-User: X-HE-Tag: 1660640086-570780 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: On 8/16/2022 10:21 AM, Haiyue Wang wrote: > 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 > Reviewed-by: "Huang, Ying" > --- Looks good to me. Reviewed-by: Baolin Wang > 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; > }