From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 9A675262FC0 for ; Tue, 16 Sep 2025 03:09:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757992149; cv=none; b=U6SE+W0JZv6nLhT0qOS3l4X6x1wewW3SRkT+t9VyMdnnj4kJ0DWmwwE4lHEmf6siFv/teaTzeaCId2NsHd1uE2sL4w0488XT6ZSaV3oqjXojGrAXuKWB5K4lzvdJDp+AXRSqXnhTCFOrHzSVrDCex4EZYRUft2YzdUZzfcMtNzg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757992149; c=relaxed/simple; bh=19anzK0snZZAQsW5P4yWBkSWgG4MjiP/1jc/fK51rkY=; h=Date:To:From:Subject:Message-Id; b=B/amTlou/q64nqXNqbNdki+vaQ9TwejbVCvIapOlD2YFuZ9w2nK66GzZ1hpj5dVMRfiLvn7DkZQCycZdRTm/O7vET51OvzQTdSLQiq3hjzJbF4nDj52gZo6O8qWY08Nkq+VC9DHwJPinmYf/FdjqG39sDchizlppmOrGagm6AIc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=bcxg02Gw; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="bcxg02Gw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 13DB8C4CEF1; Tue, 16 Sep 2025 03:09:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1757992149; bh=19anzK0snZZAQsW5P4yWBkSWgG4MjiP/1jc/fK51rkY=; h=Date:To:From:Subject:From; b=bcxg02GwCPpsFrUHguTyUJO05OM1+rYDu1LJ+MZPLem9JB3MfBuVICmurdYq82LZ8 TPxVxouQgvNz8npD4IBdTTjptmFVuVBytPz8UbLzNfbsMLKY99nZ/R1w5H3K/EH44u PKWuFnkCJFueTteu08pn7j8DMmn3Fe2y3nBpkBF0= Date: Mon, 15 Sep 2025 20:09:08 -0700 To: mm-commits@vger.kernel.org,osalvador@suse.de,muchun.song@linux.dev,liushixin2@huawei.com,jannh@google.com,harry.yoo@oracle.com,david@redhat.com,jane.chu@oracle.com,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-hugetlb-fix-copy_hugetlb_page_range-to-use-pt_share_count.patch added to mm-hotfixes-unstable branch Message-Id: <20250916030909.13DB8C4CEF1@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/hugetlb: fix copy_hugetlb_page_range() to use ->pt_share_count has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-hugetlb-fix-copy_hugetlb_page_range-to-use-pt_share_count.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-fix-copy_hugetlb_page_range-to-use-pt_share_count.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Jane Chu Subject: mm/hugetlb: fix copy_hugetlb_page_range() to use ->pt_share_count Date: Mon, 15 Sep 2025 18:45:20 -0600 commit 59d9094df3d79 ("mm: hugetlb: independent PMD page table shared count") introduced ->pt_share_count dedicated to hugetlb PMD share count tracking, but omitted fixing copy_hugetlb_page_range(), leaving the function relying on page_count() for tracking that no longer works. When lazy page table copy for hugetlb is disabled, that is, revert commit bcd51a3c679d ("hugetlb: lazy page table copies in fork()") fork()'ing with hugetlb PMD sharing quickly lockup - [ 239.446559] watchdog: BUG: soft lockup - CPU#75 stuck for 27s! [ 239.446611] RIP: 0010:native_queued_spin_lock_slowpath+0x7e/0x2e0 [ 239.446631] Call Trace: [ 239.446633] [ 239.446636] _raw_spin_lock+0x3f/0x60 [ 239.446639] copy_hugetlb_page_range+0x258/0xb50 [ 239.446645] copy_page_range+0x22b/0x2c0 [ 239.446651] dup_mmap+0x3e2/0x770 [ 239.446654] dup_mm.constprop.0+0x5e/0x230 [ 239.446657] copy_process+0xd17/0x1760 [ 239.446660] kernel_clone+0xc0/0x3e0 [ 239.446661] __do_sys_clone+0x65/0xa0 [ 239.446664] do_syscall_64+0x82/0x930 [ 239.446668] ? count_memcg_events+0xd2/0x190 [ 239.446671] ? syscall_trace_enter+0x14e/0x1f0 [ 239.446676] ? syscall_exit_work+0x118/0x150 [ 239.446677] ? arch_exit_to_user_mode_prepare.constprop.0+0x9/0xb0 [ 239.446681] ? clear_bhb_loop+0x30/0x80 [ 239.446684] ? clear_bhb_loop+0x30/0x80 [ 239.446686] entry_SYSCALL_64_after_hwframe+0x76/0x7e There are two options to resolve the potential latent issue: 1. warn against PMD sharing in copy_hugetlb_page_range(), 2. fix it. This patch opts for the second option. While at it, simplify the comment, the details are not actually relevant anymore. Link: https://lkml.kernel.org/r/20250916004520.1604530-1-jane.chu@oracle.com Fixes: 59d9094df3d79 ("mm: hugetlb: independent PMD page table shared count") Signed-off-by: Jane Chu Reviewed-by: Harry Yoo Cc: David Hildenbrand Cc: Jann Horn Cc: Liu Shixin Cc: Muchun Song Cc: Oscar Salvador Signed-off-by: Andrew Morton --- include/linux/mm_types.h | 5 +++++ mm/hugetlb.c | 15 +++++---------- 2 files changed, 10 insertions(+), 10 deletions(-) --- a/include/linux/mm_types.h~mm-hugetlb-fix-copy_hugetlb_page_range-to-use-pt_share_count +++ a/include/linux/mm_types.h @@ -631,6 +631,11 @@ static inline int ptdesc_pmd_pts_count(s { return atomic_read(&ptdesc->pt_share_count); } + +static inline bool ptdesc_pmd_is_shared(struct ptdesc *ptdesc) +{ + return !!ptdesc_pmd_pts_count(ptdesc); +} #else static inline void ptdesc_pmd_pts_init(struct ptdesc *ptdesc) { --- a/mm/hugetlb.c~mm-hugetlb-fix-copy_hugetlb_page_range-to-use-pt_share_count +++ a/mm/hugetlb.c @@ -5594,18 +5594,13 @@ int copy_hugetlb_page_range(struct mm_st break; } - /* - * If the pagetables are shared don't copy or take references. - * - * dst_pte == src_pte is the common case of src/dest sharing. - * However, src could have 'unshared' and dst shares with - * another vma. So page_count of ptep page is checked instead - * to reliably determine whether pte is shared. - */ - if (page_count(virt_to_page(dst_pte)) > 1) { +#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING + /* If the pagetables are shared, there is nothing to do */ + if (ptdesc_pmd_is_shared(virt_to_ptdesc(dst_pte))) { addr |= last_addr_mask; continue; } +#endif dst_ptl = huge_pte_lock(h, dst, dst_pte); src_ptl = huge_pte_lockptr(h, src, src_pte); @@ -7602,7 +7597,7 @@ int huge_pmd_unshare(struct mm_struct *m hugetlb_vma_assert_locked(vma); if (sz != PMD_SIZE) return 0; - if (!ptdesc_pmd_pts_count(virt_to_ptdesc(ptep))) + if (!ptdesc_pmd_is_shared(virt_to_ptdesc(ptep))) return 0; pud_clear(pud); _ Patches currently in -mm which might be from jane.chu@oracle.com are mm-hugetlb-fix-copy_hugetlb_page_range-to-use-pt_share_count.patch