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[70.31.27.79]) by smtp.gmail.com with ESMTPSA id u7-20020a05620a430700b006eed75805a2sm1491342qko.126.2022.11.17.17.10.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Nov 2022 17:10:40 -0800 (PST) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Rik van Riel , Muchun Song , Andrew Morton , peterx@redhat.com, James Houghton , Nadav Amit , Andrea Arcangeli , David Hildenbrand , Miaohe Lin , Mike Kravetz Subject: [PATCH RFC v2 08/12] mm/hugetlb: Use hugetlb walker lock in follow_hugetlb_page() Date: Thu, 17 Nov 2022 20:10:21 -0500 Message-Id: <20221118011025.2178986-9-peterx@redhat.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20221118011025.2178986-1-peterx@redhat.com> References: <20221118011025.2178986-1-peterx@redhat.com> MIME-Version: 1.0 Content-type: text/plain Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hugetlb walker lock makes sure the pte_t* won't go away from under us. Some trick is used to release the walker lock slightly earlier when we found present pte. Signed-off-by: Peter Xu --- mm/hugetlb.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index fc49e3ca8acd..e81af6a46c59 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6280,6 +6280,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, break; } + hugetlb_walker_lock(); /* * Some archs (sparc64, sh*) have multiple pte_ts to * each hugepage. We have to make sure we get the @@ -6304,6 +6305,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, !hugetlbfs_pagecache_present(h, vma, vaddr)) { if (pte) spin_unlock(ptl); + hugetlb_walker_unlock(); remainder = 0; break; } @@ -6325,6 +6327,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, if (pte) spin_unlock(ptl); + hugetlb_walker_unlock(); + if (flags & FOLL_WRITE) fault_flags |= FAULT_FLAG_WRITE; else if (unshare) @@ -6367,6 +6371,15 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, continue; } + /* + * When reach here, it means the pteval is not absent, so + * anyone who wants to free and invalidate the pgtable page + * (aka, pte*) should need to first unmap the entries which + * relies on the pgtable lock. Since we're holding it, + * we're safe even without the walker lock anymore. + */ + hugetlb_walker_unlock(); + pfn_offset = (vaddr & ~huge_page_mask(h)) >> PAGE_SHIFT; page = pte_page(huge_ptep_get(pte)); -- 2.37.3