From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5BD93CD4F54 for ; Thu, 5 Sep 2024 06:35:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:To:References:Message-Id: Content-Transfer-Encoding:Cc:Date:In-Reply-To:From:Subject:Mime-Version: Content-Type:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=ksx22GPeHsqr/AARD3Kz3GMedfunDXYI9hMA6uigG5g=; b=0YyY7VBlbhSiS7RwjF7yqI2BjD cCGPyBqCdRpLfM0JHvQEC2j4zhJ6aXNpYEWZvOA6NiJdBqtO21seCxP1ZzJiLc27OKB/fr648vON8 7XRireT9bGPZoVZpxvtwqhbs+G7gj1ZQq40GdlhizVvmU/3DDvM105xyp8pzu8o0OBE8gQoYxFL1Q jjliW8+RaasgT8yqkGT0N/XbmK+NinC4Y+YyY97aqtTzyjJE3etiRt8stbVNVgqdpL8O1Yu1bXtcJ fp0vx0+ZUkxoMOU9yoqt7D5qBLbZeXt7aO28TJuHnclWxZ8WfBZJBxz0S6K3rrZdw/VsKDqWLtyng zWv9c++Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sm65B-00000007C8u-1b2N; Thu, 05 Sep 2024 06:35:05 +0000 Received: from out-187.mta0.migadu.com ([91.218.175.187]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1sm63h-00000007Brg-0Vve for linux-arm-kernel@lists.infradead.org; Thu, 05 Sep 2024 06:33:35 +0000 Content-Type: text/plain; charset=us-ascii DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1725518009; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ksx22GPeHsqr/AARD3Kz3GMedfunDXYI9hMA6uigG5g=; b=RLu7mycFOgF59AgkyN6sSQyBId6kbznssyisAv642gvR8ipqt29Lkad550xwM3XC5i0xuy w6vXjYG+TmTANMF23rlD1fddyYK7eqC0z5dDGe19Hl9oqA7jJgbrpuYJ7VxlJVwrKc2DzX 9JP+wn68fbsvBkV8OiiriUiBUa01AUs= Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3776.700.51\)) Subject: Re: [PATCH v2 07/14] mm: khugepaged: collapse_pte_mapped_thp() use pte_offset_map_rw_nolock() X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Muchun Song In-Reply-To: Date: Thu, 5 Sep 2024 14:32:48 +0800 Cc: David Hildenbrand , Hugh Dickins , Matthew Wilcox , "Vlastimil Babka (SUSE)" , Andrew Morton , Mike Rapoport , Vishal Moola , Peter Xu , Ryan Roberts , christophe.leroy2@cs-soprasteria.com, LKML , Linux Memory Management List , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org Content-Transfer-Encoding: quoted-printable Message-Id: <05955456-8743-448A-B7A4-BC45FABEA628@linux.dev> References: <24be821f-a95f-47f1-879a-c392a79072cc@linux.dev> To: Qi Zheng X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240904_233333_485931_96FD29BF X-CRM114-Status: GOOD ( 19.24 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org > On Aug 30, 2024, at 14:54, Qi Zheng = wrote: >=20 >=20 >=20 > On 2024/8/29 16:10, Muchun Song wrote: >> On 2024/8/22 15:13, Qi Zheng wrote: >>> In collapse_pte_mapped_thp(), we may modify the pte and pmd entry = after >>> acquring the ptl, so convert it to using pte_offset_map_rw_nolock(). = At >>> this time, the write lock of mmap_lock is not held, and the = pte_same() >>> check is not performed after the PTL held. So we should get pgt_pmd = and do >>> pmd_same() check after the ptl held. >>>=20 >>> For the case where the ptl is released first and then the pml is = acquired, >>> the PTE page may have been freed, so we must do pmd_same() check = before >>> reacquiring the ptl. >>>=20 >>> Signed-off-by: Qi Zheng >>> --- >>> mm/khugepaged.c | 16 +++++++++++++++- >>> 1 file changed, 15 insertions(+), 1 deletion(-) >>>=20 >>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >>> index 53bfa7f4b7f82..15d3f7f3c65f2 100644 >>> --- a/mm/khugepaged.c >>> +++ b/mm/khugepaged.c >>> @@ -1604,7 +1604,7 @@ int collapse_pte_mapped_thp(struct mm_struct = *mm, unsigned long addr, >>> if (userfaultfd_armed(vma) && !(vma->vm_flags & VM_SHARED)) >>> pml =3D pmd_lock(mm, pmd); >>> - start_pte =3D pte_offset_map_nolock(mm, pmd, haddr, &ptl); >>> + start_pte =3D pte_offset_map_rw_nolock(mm, pmd, haddr, = &pgt_pmd, &ptl); >>> if (!start_pte) /* mmap_lock + page lock should prevent = this */ >>> goto abort; >>> if (!pml) >>> @@ -1612,6 +1612,9 @@ int collapse_pte_mapped_thp(struct mm_struct = *mm, unsigned long addr, >>> else if (ptl !=3D pml) >>> spin_lock_nested(ptl, SINGLE_DEPTH_NESTING); >>> + if (unlikely(!pmd_same(pgt_pmd, pmdp_get_lockless(pmd)))) >>> + goto abort; >>> + >>> /* step 2: clear page table and adjust rmap */ >>> for (i =3D 0, addr =3D haddr, pte =3D start_pte; >>> i < HPAGE_PMD_NR; i++, addr +=3D PAGE_SIZE, pte++) { >>> @@ -1657,6 +1660,16 @@ int collapse_pte_mapped_thp(struct mm_struct = *mm, unsigned long addr, >>> /* step 4: remove empty page table */ >>> if (!pml) { >>> pml =3D pmd_lock(mm, pmd); >>> + /* >>> + * We called pte_unmap() and release the ptl before = acquiring >>> + * the pml, which means we left the RCU critical section, = so the >>> + * PTE page may have been freed, so we must do pmd_same() = check >>> + * before reacquiring the ptl. >>> + */ >>> + if (unlikely(!pmd_same(pgt_pmd, pmdp_get_lockless(pmd)))) { >>> + spin_unlock(pml); >>> + goto pmd_change; >> Seems we forget to flush TLB since we've cleared some pte entry? >=20 > See comment above the ptep_clear(): >=20 > /* > * Must clear entry, or a racing truncate may re-remove it. > * TLB flush can be left until pmdp_collapse_flush() does it. > * PTE dirty? Shmem page is already dirty; file is read-only. > */ >=20 > The TLB flush was handed over to pmdp_collapse_flush(). If a But you skipped pmdp_collapse_flush(). > concurrent thread free the PTE page at this time, the TLB will > also be flushed after pmd_clear(). >=20 >>> + } >>> if (ptl !=3D pml) >>> spin_lock_nested(ptl, SINGLE_DEPTH_NESTING); >>> } >>> @@ -1688,6 +1701,7 @@ int collapse_pte_mapped_thp(struct mm_struct = *mm, unsigned long addr, >>> pte_unmap_unlock(start_pte, ptl); >>> if (pml && pml !=3D ptl) >>> spin_unlock(pml); >>> +pmd_change: >>> if (notified) >>> mmu_notifier_invalidate_range_end(&range); >>> drop_folio: