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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 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-type: text/plain X-Rspam-User: X-Spamd-Result: default: False [7.55 / 9.00]; SORBS_IRL_BL(3.00)[209.85.219.71:received]; R_MISSING_CHARSET(2.50)[]; BAYES_HAM(-1.55)[84.40%]; SUSPICIOUS_RECIPS(1.50)[]; MID_CONTAINS_FROM(1.00)[]; SUBJECT_HAS_UNDERSCORES(1.00)[]; RCVD_NO_TLS_LAST(0.10)[]; MIME_GOOD(-0.10)[text/plain]; BAD_REP_POLICIES(0.10)[]; PREVIOUSLY_DELIVERED(0.00)[linux-mm@kvack.org]; ARC_NA(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_TWELVE(0.00)[14]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_ALLOW(0.00)[redhat.com:s=mimecast20190719]; MIME_TRACE(0.00)[0:+]; TAGGED_RCPT(0.00)[]; DMARC_POLICY_ALLOW(0.00)[redhat.com,none]; TO_MATCH_ENVRCPT_SOME(0.00)[]; ARC_SIGNED(0.00)[hostedemail.com:s=arc-20220608:i=1]; DKIM_TRACE(0.00)[redhat.com:+]; R_SPF_ALLOW(0.00)[+ip4:170.10.133.0/24]; RCVD_COUNT_THREE(0.00)[4]; TO_DN_SOME(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[] X-Rspamd-Queue-Id: 3E0CFA0015 X-Rspamd-Server: rspam01 X-Stat-Signature: 45niftg3o3as3ygjzg4cikweegm95nom X-HE-Tag: 1670445123-448413 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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;