From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga06-in.huawei.com (szxga06-in.huawei.com [45.249.212.32]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 431B384D3E for ; Tue, 17 Dec 2024 01:42:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.32 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734399755; cv=none; b=iOk37v7GvA4mC0HEo7jVtOY9/KV6tN/zIAmgb5QY7UuuQ87qTk07oSkHiFRlu/5qmSSH+EkSHxl8cGcPMwKIoLXBqDBgZMtcSIY/8kKPCCJFtgfIte6j7G9D4ITUGqlQaLeeclGCELkdEBPME1UMzN70kLx/3TWbOtOE1/DEmmY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734399755; c=relaxed/simple; bh=Ex+cyQq3a4nJEwGaPpVIHeJAOLuM77xmseUnFdBHamM=; h=Subject:To:References:CC:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=tGgHwsSkElUpVjz28F+3pWz+4AdjI0yzNIJhZb3r15WlMhje//Q3Y/znDHlkOgKYcp2Xn0kQYiSymnURLCbE/YtXbAPZUl8vtseVdpgfSK/m016LyzpxferYs44xqGHks5tNJvT7DeaW36UMzKclhkS3FH1EUj+oF7pMezXc/Ds= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.32 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.163.17]) by szxga06-in.huawei.com (SkyGuard) with ESMTP id 4YC01f2Tcjz20m8G; Tue, 17 Dec 2024 09:42:46 +0800 (CST) Received: from kwepemg200013.china.huawei.com (unknown [7.202.181.64]) by mail.maildlp.com (Postfix) with ESMTPS id 3B3FF1A0188; Tue, 17 Dec 2024 09:42:28 +0800 (CST) Received: from [10.174.179.24] (10.174.179.24) by kwepemg200013.china.huawei.com (7.202.181.64) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 17 Dec 2024 09:42:27 +0800 Subject: Re: [PATCH v2] mm: hugetlb: independent PMD page table shared count To: , Andrew Morton , Muchun Song , Kenneth W Chen , Kefeng Wang , Nanyong Sun References: <20241216071147.3984217-1-liushixin2@huawei.com> CC: , From: Liu Shixin Message-ID: <060c21b2-3138-15c0-66ff-42895bb956f6@huawei.com> Date: Tue, 17 Dec 2024 09:42:26 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To kwepemg200013.china.huawei.com (7.202.181.64) On 2024/12/17 8:04, jane.chu@oracle.com wrote: > On 12/15/2024 11:11 PM, Liu Shixin wrote: > >> The folio refcount may be increased unexpectly through try_get_folio() by >> caller such as split_huge_pages. In huge_pmd_unshare(), we use refcount to >> check whether a pmd page table is shared. The check is incorrect if the >> refcount is increased by the above caller, and this can cause the page >> table leaked: >> >> BUG: Bad page state in process sh pfn:109324 >> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x66 pfn:0x109324 >> flags: 0x17ffff800000000(node=0|zone=2|lastcpupid=0xfffff) >> page_type: f2(table) >> raw: 017ffff800000000 0000000000000000 0000000000000000 0000000000000000 >> raw: 0000000000000066 0000000000000000 00000000f2000000 0000000000000000 >> page dumped because: nonzero mapcount >> ... >> CPU: 31 UID: 0 PID: 7515 Comm: sh Kdump: loaded Tainted: G B 6.13.0-rc2master+ #7 >> Tainted: [B]=BAD_PAGE >> Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015 >> Call trace: >> show_stack+0x20/0x38 (C) >> dump_stack_lvl+0x80/0xf8 >> dump_stack+0x18/0x28 >> bad_page+0x8c/0x130 >> free_page_is_bad_report+0xa4/0xb0 >> free_unref_page+0x3cc/0x620 >> __folio_put+0xf4/0x158 >> split_huge_pages_all+0x1e0/0x3e8 >> split_huge_pages_write+0x25c/0x2d8 >> full_proxy_write+0x64/0xd8 >> vfs_write+0xcc/0x280 >> ksys_write+0x70/0x110 >> __arm64_sys_write+0x24/0x38 >> invoke_syscall+0x50/0x120 >> el0_svc_common.constprop.0+0xc8/0xf0 >> do_el0_svc+0x24/0x38 >> el0_svc+0x34/0x128 >> el0t_64_sync_handler+0xc8/0xd0 >> el0t_64_sync+0x190/0x198 >> >> The issue may be triggered by damon, offline_page, page_idle, etc, which >> will increase the refcount of page table. >> >> Fix it by introducing independent PMD page table shared count. >> As described by comment, pt_index/pt_mm/pt_frag_refcount are used for >> s390 gmap, x86 pgds and powerpc, pt_share_count is used for x86/arm64/riscv >> pmds, so we can reuse the field as pt_share_count. >> >> Fixes: 39dde65c9940 ("[PATCH] shared page table for hugetlb page") >> Signed-off-by: Liu Shixin >> --- >> v1->v2: Fix build error when !CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING and >> modify the changelog. > > Sorry for having missed v2 when I responded, the same question remains - > > https://lore.kernel.org/linux-mm/202412151541.SQEZStgy-lkp@intel.com/T/#m90c26215594e494f5c65c3fa71979b519f0c8481 > > thanks, > > -jane There's no overlap and the problem has nothing with THP. split_huge_pages refers to the debugfs file. In huge_pmd_unshare(), we use refcount to determine whether a page table is sharing, but the split_huge_pages_all() increased the refcount. As a results, we treat an unshared page table as shared, and eventually miss freeing the page mapped by this page table. thanks, > >> >> include/linux/mm.h | 1 + >> include/linux/mm_types.h | 30 ++++++++++++++++++++++++++++++ >> mm/hugetlb.c | 16 +++++++--------- >> 3 files changed, 38 insertions(+), 9 deletions(-) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index c39c4945946c..50fbf2a1b0ad 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -3115,6 +3115,7 @@ static inline bool pagetable_pmd_ctor(struct ptdesc *ptdesc) >> if (!pmd_ptlock_init(ptdesc)) >> return false; >> __folio_set_pgtable(folio); >> + ptdesc_pmd_pts_init(ptdesc); >> lruvec_stat_add_folio(folio, NR_PAGETABLE); >> return true; >> } >> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h >> index 7361a8f3ab68..332cee285662 100644 >> --- a/include/linux/mm_types.h >> +++ b/include/linux/mm_types.h >> @@ -445,6 +445,7 @@ FOLIO_MATCH(compound_head, _head_2a); >> * @pt_index: Used for s390 gmap. >> * @pt_mm: Used for x86 pgds. >> * @pt_frag_refcount: For fragmented page table tracking. Powerpc only. >> + * @pt_share_count: Used for HugeTLB PMD page table share count. >> * @_pt_pad_2: Padding to ensure proper alignment. >> * @ptl: Lock for the page table. >> * @__page_type: Same as page->page_type. Unused for page tables. >> @@ -471,6 +472,9 @@ struct ptdesc { >> pgoff_t pt_index; >> struct mm_struct *pt_mm; >> atomic_t pt_frag_refcount; >> +#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING >> + atomic_t pt_share_count; >> +#endif >> }; >> union { >> @@ -516,6 +520,32 @@ static_assert(sizeof(struct ptdesc) <= sizeof(struct page)); >> const struct page *: (const struct ptdesc *)(p), \ >> struct page *: (struct ptdesc *)(p))) >> +#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING >> +static inline void ptdesc_pmd_pts_init(struct ptdesc *ptdesc) >> +{ >> + atomic_set(&ptdesc->pt_share_count, 0); >> +} >> + >> +static inline void ptdesc_pmd_pts_inc(struct ptdesc *ptdesc) >> +{ >> + atomic_inc(&ptdesc->pt_share_count); >> +} >> + >> +static inline void ptdesc_pmd_pts_dec(struct ptdesc *ptdesc) >> +{ >> + atomic_dec(&ptdesc->pt_share_count); >> +} >> + >> +static inline int ptdesc_pmd_pts_count(struct ptdesc *ptdesc) >> +{ >> + return atomic_read(&ptdesc->pt_share_count); >> +} >> +#else >> +static inline void ptdesc_pmd_pts_init(struct ptdesc *ptdesc) >> +{ >> +} >> +#endif >> + >> /* >> * Used for sizing the vmemmap region on some architectures >> */ >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index ea2ed8e301ef..60846b060b87 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -7212,7 +7212,7 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma, >> spte = hugetlb_walk(svma, saddr, >> vma_mmu_pagesize(svma)); >> if (spte) { >> - get_page(virt_to_page(spte)); >> + ptdesc_pmd_pts_inc(virt_to_ptdesc(spte)); >> break; >> } >> } >> @@ -7227,7 +7227,7 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma, >> (pmd_t *)((unsigned long)spte & PAGE_MASK)); >> mm_inc_nr_pmds(mm); >> } else { >> - put_page(virt_to_page(spte)); >> + ptdesc_pmd_pts_dec(virt_to_ptdesc(spte)); >> } >> spin_unlock(&mm->page_table_lock); >> out: >> @@ -7239,10 +7239,6 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma, >> /* >> * unmap huge page backed by shared pte. >> * >> - * Hugetlb pte page is ref counted at the time of mapping. If pte is shared >> - * indicated by page_count > 1, unmap is achieved by clearing pud and >> - * decrementing the ref count. If count == 1, the pte page is not shared. >> - * >> * Called with page table lock held. >> * >> * returns: 1 successfully unmapped a shared pte page >> @@ -7251,18 +7247,20 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma, >> int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, >> unsigned long addr, pte_t *ptep) >> { >> + unsigned long sz = huge_page_size(hstate_vma(vma)); >> pgd_t *pgd = pgd_offset(mm, addr); >> p4d_t *p4d = p4d_offset(pgd, addr); >> pud_t *pud = pud_offset(p4d, addr); >> i_mmap_assert_write_locked(vma->vm_file->f_mapping); >> hugetlb_vma_assert_locked(vma); >> - BUG_ON(page_count(virt_to_page(ptep)) == 0); >> - if (page_count(virt_to_page(ptep)) == 1) >> + if (sz != PMD_SIZE) >> + return 0; >> + if (!ptdesc_pmd_pts_count(virt_to_ptdesc(ptep))) >> return 0; >> pud_clear(pud); >> - put_page(virt_to_page(ptep)); >> + ptdesc_pmd_pts_dec(virt_to_ptdesc(ptep)); >> mm_dec_nr_pmds(mm); >> return 1; >> } > > . >