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(p200300cbc710970070037e4d43dd7bfd.dip0.t-ipconnect.de. [2003:cb:c710:9700:7003:7e4d:43dd:7bfd]) by smtp.gmail.com with ESMTPSA id h2-20020adff4c2000000b0030631f199f9sm4497510wrp.34.2023.05.26.02.12.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 26 May 2023 02:12:17 -0700 (PDT) Message-ID: Date: Fri, 26 May 2023 11:12:16 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: mm: Question: pte SMP data race in do_anomyous_page()? To: Karim Manaouil Cc: npiggin@gmail.com, akpm@linux-foundation.org, mike.kravetz@oracle.com, linux-mm@kvack.org, Hugh Dickins , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= References: <46ad119c-b129-e983-031b-d71aacad6a20@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: 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-Rspamd-Queue-Id: 6C6B51C0007 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: zyeo8njfj4qbg866a89xt9u6mt4huzc9 X-HE-Tag: 1685092341-381773 X-HE-Meta: U2FsdGVkX1/I43PRzfKcpqiLJlB+YKRj9kZzWFqELzM58VxPGfxO/+zfZ0CI5ri1n+vW/FRVpiNH8AtlD+nuuEltD3YkOSW/kImV+cQhaNI0jJNituNDIhm5XIOXZQlgvzmAHQqwvvjNhwIjoAj9NblgOyk1kFx0jeYc5B4wYAaKgKHBTVFqx1H+32f60kambFef0KaLBquTyvUVZtHmmXs1yoVSFWVGmVnSmwxAosXN8kbCGQ7UNH1U3RcDHKU/TKy5BlmE5odSU+ywQhGGkdkS6dcRFgyq6FbT7ODIomxihKS6wUkzFlti9xitLYoFzTvHoKZmJh83uDkWNE5AXAKKygWBLrSJqqo9OLt0qdr6ZRxp+quz6UCBgPdAZJ0CyEP/lgMeTYFIiHfonaN0ulw0li2ae/OvHYbS0J3R7p20htGX3EobrlUZLEbkowPSlK4AByftKxGydc7Fhdc8E3l9ZVdfK5jIFAax/qd4au3fcvHetiKSi6tHsL8nkOAAo4+4WHftBLoyAl8J+oCI2NSuM0I6e6JqiVRrKsEY/7LGyCJuCE7cl1I1w+5aMuC1/YAS0RB50wBU1oecRO6wm1Z6iLu9E1IeIhObArxQdoIMuyxDzVQ5dUmcosuOLRkzjfIZKNaT5mq/ndRQDmgJ5gdAvL+bzgAvL6rdOtpqhZ5ltbBUGfxzoTFqqAl58SVySlWTQ5wI+q3GzubHreNbBl/mlfO35Vj32S9SK7UBnhT+NXhpGddw/cprvNzM9EZuT5UczwP6Y74ZcWKiCC+bCLNPhzMjOKdkbmi1yz8yYQGwBpq+TrqibyLYeaaNav+1N2UEDEgDkhNz16JNeWw2NDkgVzQfKrfxx17VWCFXrRJcQVNsJZG+MD79xoKdHAT8gi2/KPAWp55c6VqZUpQSxJ5jPXIs2utI1GZy38ezliLzxQxFvSqNsPgmHxjGgMQCQi85k0gufPdnaRdJxGx PaGKHr4c a9cJ11zGSrtwnV/IvJC7XIjOsr1l+2eCAjzuk+BCDfAaRVQVfJJbWGaeEugBsDb61E4POTyk8h8DoeobfN6ETg+pZEOVvqMIqd2dO7Zycr8zYDwK2Mp5T1seMexw3Y3XkURXdoDUGPJAABRDz4DPb0XjLfZCKCkL+UZdtIJRFsq5R6cZM7jL+jM2O6cJJd+1CFrvVHI1bldjWuEs6bwQyA+m25nM53uLQBjGaEKrAPipqfaHUUlqsIMbcigK9CHUoIA5M62UjV/Zg3dqZWB8uekVKBheEOtk4IIa4AK3S5/U/XIBBm+1SqD3Pr3qr1IdEKOYmqGp/u50RVExS8QgY80vV3AqFlU3hiC9sUsAi6iap03MsR9PHfmlJIssIxicTuB2dtZxfsmSdwo5QV0vNeeedfjkc/h4tDwpru6EVNoJoX5ATEg1/pUZo2yDzg/uha/dhOVwSBjaP9zW6JXiANSFtDQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000145, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 26.05.23 11:07, Karim Manaouil wrote: > On Thu, May 25, 2023 at 02:55:30PM +0200, David Hildenbrand wrote: >> On 25.05.23 12:06, Karim Manaouil wrote: >>> Hi, >>> >>> In do_anonymous_page(), a new page is allocated and zeroed, and the >>> corresponding page struct is initialised (setting flags PageUptodate, >>> PageSwapBacked, etc. and initialising the various counters). >>> >>> Then, set_pte_at() is called directly without calling smp_wmb() to make >>> the updates above visible on other CPUs. >>> >>> This could race with a page table walker. The walker can read the new pte >>> and try to access the page struct or the page content before the changes >>> above were made visible. >> >> Only after acquiring the page table lock (which the writer first has to >> release), right? > > In many cases, the walkers don't take the page table locks (e.g. > mm/hmm.c). Looks like we really should be locking the page table in hmm_vma_walk_pmd() instead of only doing a pte_offset_map(). It's all very racy without that ... Even the !pte_present(pte) check is racy ... -- Thanks, David / dhildenb