From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from vmicros1.altlinux.org (vmicros1.altlinux.org [194.107.17.57]) by smtp.subspace.kernel.org (Postfix) with ESMTP id BD3951E412A for ; Sun, 29 Jun 2025 13:07:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=194.107.17.57 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751202464; cv=none; b=Ir+DjdA6K2Z4ka2yjv6hpZs+Tx4DRDF7ziZ44LvPBSjj1CZFoTgbqm1rRwp9hc+EhtoI9mjcKkxFPG2rMjVK/xGZhFM1KqczhyHGF7bi3lNjT2g7/PNJmp+2toFHzJQJxRhLXq/3un0nnRZfNCcKpRfpzvyP43DbO5gDgkRUaH4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751202464; c=relaxed/simple; bh=dETYPqnfeExW+bmSLqP4SP1nKeGy7MP7b4bqwqTzBcg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=TSp5WkdnRvEBEbOwnQAVPVOHB5J2Mx8dfZzEUrUQW7K2ldDeueXNjbhuvRvYuL8rtO7DJnFUzODt7mQRW/dcwYzv73ixzEhgIdUfYN8tCbwOGI0BMJ5bg3YXzgRN6hk7zWLL825ntQxfSTk15bSi5w+qN8m4KPJA6w3Pzzstwr0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=altlinux.org; spf=pass smtp.mailfrom=altlinux.org; arc=none smtp.client-ip=194.107.17.57 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=altlinux.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=altlinux.org Received: from imap.altlinux.org (imap.altlinux.org [194.107.17.38]) by vmicros1.altlinux.org (Postfix) with ESMTP id 6E94172C8F5; Sun, 29 Jun 2025 16:00:46 +0300 (MSK) Received: from pony.office.basealt.ru (unknown [193.43.10.9]) by imap.altlinux.org (Postfix) with ESMTPSA id 63C8F36D0184; Sun, 29 Jun 2025 16:00:46 +0300 (MSK) Received: by pony.office.basealt.ru (Postfix, from userid 500) id 47C73360D500; Sun, 29 Jun 2025 16:00:46 +0300 (MSK) Date: Sun, 29 Jun 2025 16:00:46 +0300 From: Vitaly Chikunov To: Jann Horn , Sasha Levin , Andrew Morton , gregkh@linuxfoundation.org, stable@vger.kernel.org Cc: Jane Chu , Nanyong Sun , Muchun Song , Ken Chen , Kefeng Wang , Liu Shixin , linux-mm@kvack.org Subject: Re: [PATCH 6.1.y 2/3] mm: hugetlb: independent PMD page table shared count Message-ID: References: <2025062041-uplifted-cahoots-6c42@gregkh> <20250620213334.158850-1-jannh@google.com> <20250620213334.158850-2-jannh@google.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250620213334.158850-2-jannh@google.com> Hi, LTP tests failure with the following commit described below: On Fri, Jun 20, 2025 at 11:33:32PM +0200, Jann Horn wrote: > From: Liu Shixin > > [ Upstream commit 59d9094df3d79443937add8700b2ef1a866b1081 ] > > 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. > > 1. The page table itself will be discarded after reporting the > "nonzero mapcount". > > 2. The HugeTLB page mapped by the page table miss freeing since we > treat the page table as shared and a shared page table will not be > unmapped. > > 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. The commit causes LTP test memfd_create03 to fail on i586 architecture on v6.1.142 stable release, the test was passing on v6.1.141. Found the commit with git bisect. The failure: root@i586:~# /usr/lib/ltp/testcases/bin/memfd_create03 tst_hugepage.c:78: TINFO: 2 hugepage(s) reserved tst_test.c:1526: TINFO: Timeout per run is 0h 00m 30s memfd_create03.c:171: TINFO: --TESTING WRITE CALL IN HUGEPAGES-- memfd_create03.c:176: TINFO: memfd_create() succeeded memfd_create03.c:70: TPASS: write(3, "LTP", 3) failed as expected memfd_create03.c:171: TINFO: --TESTING PAGE SIZE OF CREATED FILE-- memfd_create03.c:176: TINFO: memfd_create() succeeded memfd_create03.c:43: TINFO: mmap((nil), 4194304, 2, 2, 3, 0) succeeded memfd_create03.c:92: TINFO: munmap(0xb7800000, 1024kB) failed as expected memfd_create03.c:92: TINFO: munmap(0xb7800000, 2048kB) failed as expected memfd_create03.c:92: TINFO: munmap(0xb7800000, 3072kB) failed as expected memfd_create03.c:111: TPASS: munmap() fails for page sizes less than 4096kB memfd_create03.c:171: TINFO: --TESTING HUGEPAGE ALLOCATION LIMIT-- memfd_create03.c:176: TINFO: memfd_create() succeeded memfd_create03.c:39: TBROK: mmap((nil),0,2,2,3,0) failed: EINVAL (22) Summary: passed 2 failed 0 broken 1 skipped 0 warnings 0 dmesg while the test run: [ 16.072078] memfd_create03 (203): drop_caches: 3 [ 16.075298] mm/pgtable-generic.c:51: bad pgd 7d4000e7 The same error occurs for v5.10.239. There is no test failure on v6.12.35 nor v6.15.4 even though they contain the same commit. Thanks, > > Link: https://lkml.kernel.org/r/20241216071147.3984217-1-liushixin2@huawei.com > Fixes: 39dde65c9940 ("[PATCH] shared page table for hugetlb page") > Signed-off-by: Liu Shixin > Cc: Kefeng Wang > Cc: Ken Chen > Cc: Muchun Song > Cc: Nanyong Sun > Cc: Jane Chu > Cc: > Signed-off-by: Andrew Morton > Signed-off-by: Sasha Levin > [backport note: struct ptdesc did not exist yet, stuff it equivalently > into struct page instead] > Signed-off-by: Jann Horn > --- > include/linux/mm.h | 3 +++ > include/linux/mm_types.h | 3 +++ > mm/hugetlb.c | 16 +++++++--------- > 3 files changed, 13 insertions(+), 9 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 03357c196e0b..b36dffbfbe69 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2537,6 +2537,9 @@ static inline bool pgtable_pmd_page_ctor(struct page *page) > if (!pmd_ptlock_init(page)) > return false; > __SetPageTable(page); > +#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE > + atomic_set(&page->pt_share_count, 0); > +#endif > inc_lruvec_page_state(page, NR_PAGETABLE); > return true; > } > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index a9c1d611029d..9b64610eddcc 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -160,6 +160,9 @@ struct page { > union { > struct mm_struct *pt_mm; /* x86 pgds only */ > atomic_t pt_frag_refcount; /* powerpc */ > +#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE > + atomic_t pt_share_count; > +#endif > }; > #if ALLOC_SPLIT_PTLOCKS > spinlock_t *ptl; > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index fc5d3d665266..a3907edf2909 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -7114,7 +7114,7 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma, > spte = huge_pte_offset(svma->vm_mm, saddr, > vma_mmu_pagesize(svma)); > if (spte) { > - get_page(virt_to_page(spte)); > + atomic_inc(&virt_to_page(spte)->pt_share_count); > break; > } > } > @@ -7129,7 +7129,7 @@ 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)); > + atomic_dec(&virt_to_page(spte)->pt_share_count); > } > spin_unlock(ptl); > out: > @@ -7141,10 +7141,6 @@ 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 > @@ -7153,18 +7149,20 @@ 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 (!atomic_read(&virt_to_page(ptep)->pt_share_count)) > return 0; > > pud_clear(pud); > - put_page(virt_to_page(ptep)); > + atomic_dec(&virt_to_page(ptep)->pt_share_count); > mm_dec_nr_pmds(mm); > return 1; > } > -- > 2.50.0.rc2.701.gf1e915cc24-goog >