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[70.31.27.79]) by smtp.gmail.com with ESMTPSA id a1-20020ac81081000000b003a4b88b886esm2654781qtj.96.2022.10.30.14.29.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 30 Oct 2022 14:29:41 -0700 (PDT) From: Peter Xu To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Andrew Morton , James Houghton , Miaohe Lin , David Hildenbrand , Muchun Song , Andrea Arcangeli , Nadav Amit , Mike Kravetz , peterx@redhat.com, Rik van Riel Subject: [PATCH RFC 06/10] mm/hugetlb: Make page_vma_mapped_walk() RCU-safe Date: Sun, 30 Oct 2022 17:29:25 -0400 Message-Id: <20221030212929.335473-7-peterx@redhat.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20221030212929.335473-1-peterx@redhat.com> References: <20221030212929.335473-1-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 RCU makes sure the pte_t* won't go away from under us. Please refer to the comment above huge_pte_offset() for more information. Signed-off-by: Peter Xu --- include/linux/rmap.h | 3 +++ mm/page_vma_mapped.c | 7 ++++++- 2 files changed, 9 insertions(+), 1 deletion(-) diff --git a/include/linux/rmap.h b/include/linux/rmap.h index bd3504d11b15..d2c5e69a56f2 100644 --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -408,6 +408,9 @@ static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw) pte_unmap(pvmw->pte); if (pvmw->ptl) spin_unlock(pvmw->ptl); + /* Hugetlb uses RCU lock for safe access of huge_pte_offset() */ + if (is_vm_hugetlb_page(pvmw->vma)) + rcu_read_unlock(); } bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw); diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c index 93e13fc17d3c..513210a59d7b 100644 --- a/mm/page_vma_mapped.c +++ b/mm/page_vma_mapped.c @@ -169,10 +169,15 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) if (pvmw->pte) return not_found(pvmw); + /* For huge_pte_offset() */ + rcu_read_lock(); + /* when pud is not present, pte will be NULL */ pvmw->pte = huge_pte_offset(mm, pvmw->address, size); - if (!pvmw->pte) + if (!pvmw->pte) { + rcu_read_unlock(); return false; + } pvmw->ptl = huge_pte_lock(hstate, mm, pvmw->pte); if (!check_pte(pvmw)) -- 2.37.3