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[70.31.27.79]) by smtp.gmail.com with ESMTPSA id bm8-20020a05620a198800b006fa8299b4d5sm18007118qkb.100.2022.12.07.12.31.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Dec 2022 12:32:00 -0800 (PST) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Jann Horn , Andrea Arcangeli , peterx@redhat.com, James Houghton , Rik van Riel , Miaohe Lin , Nadav Amit , John Hubbard , Mike Kravetz , David Hildenbrand , Andrew Morton , Muchun Song Subject: [PATCH v2 10/10] mm/hugetlb: Document why page_vma_mapped_walk() is safe to walk Date: Wed, 7 Dec 2022 15:31:58 -0500 Message-Id: <20221207203158.651092-1-peterx@redhat.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20221207203034.650899-1-peterx@redhat.com> References: <20221207203034.650899-1-peterx@redhat.com> MIME-Version: 1.0 Content-type: text/plain X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1751589189712769753?= X-GMAIL-MSGID: =?utf-8?q?1751589189712769753?= Taking vma lock here is not needed for now because all potential hugetlb walkers here should have i_mmap_rwsem held. Document the fact. Reviewed-by: Mike Kravetz Signed-off-by: Peter Xu --- mm/page_vma_mapped.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c index e97b2e23bd28..2e59a0419d22 100644 --- a/mm/page_vma_mapped.c +++ b/mm/page_vma_mapped.c @@ -168,8 +168,14 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) /* The only possible mapping was handled on last iteration */ if (pvmw->pte) return not_found(pvmw); - - /* when pud is not present, pte will be NULL */ + /* + * NOTE: we don't need explicit lock here to walk the + * hugetlb pgtable because either (1) potential callers of + * hugetlb pvmw currently holds i_mmap_rwsem, or (2) the + * caller will not walk a hugetlb vma (e.g. ksm or uprobe). + * When one day this rule breaks, one will get a warning + * in hugetlb_walk(), and then we'll figure out what to do. + */ pvmw->pte = hugetlb_walk(vma, pvmw->address, size); if (!pvmw->pte) return false;