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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id k32-20020a05600c1ca000b003b4ff30e566sm11743772wms.3.2022.12.08.05.16.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 08 Dec 2022 05:16:04 -0800 (PST) Message-ID: <799d6831-2af3-72c1-84b2-1f0454a46c07@redhat.com> Date: Thu, 8 Dec 2022 14:16:03 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.0 Subject: Re: [PATCH v2 10/10] mm/hugetlb: Document why page_vma_mapped_walk() is safe to walk To: Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Jann Horn , Andrea Arcangeli , James Houghton , Rik van Riel , Miaohe Lin , Nadav Amit , John Hubbard , Mike Kravetz , Andrew Morton , Muchun Song References: <20221207203034.650899-1-peterx@redhat.com> <20221207203158.651092-1-peterx@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20221207203158.651092-1-peterx@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 569AE180020 X-Rspamd-Server: rspam01 X-Stat-Signature: 5g31g4opz9ci17ozrsao1dw93d3zhgua X-HE-Tag: 1670505368-545770 X-HE-Meta: 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 lFjl5XE2 bMhmU90KPBTriN9Yffbi8gsPd1kjmcqRP4AoDQ7xq4NmMy91jx5xVxHUmW54cWHKy7vAVnpLYV1AnCCtyW8rLUe3w4LuGLeU+iEkH3WD1R2QocoUmgoSAep20Eco+Pa7pw+QL0AtItFWt3k2UvouG+GRV8RwsBBLMykR6e+0bDpTWLKw= 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: On 07.12.22 21:31, Peter Xu wrote: > 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; Would it make sense to squash that into the previous commit? -- Thanks, David / dhildenb