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[2003:cb:c700:2400:6b79:2aa:9602:7016]) by smtp.gmail.com with ESMTPSA id e14-20020adfef0e000000b003063938bf7bsm1389765wro.86.2023.05.02.05.47.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 May 2023 05:47:25 -0700 (PDT) Message-ID: Date: Tue, 2 May 2023 14:47:22 +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: [PATCH v6 3/3] mm/gup: disallow FOLL_LONGTERM GUP-fast writing to file-backed mappings To: Peter Zijlstra , Lorenzo Stoakes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Jason Gunthorpe , Jens Axboe , Matthew Wilcox , Dennis Dalessandro , Leon Romanovsky , Christian Benvenuti , Nelson Escobar , Bernard Metzler , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Adrian Hunter , Bjorn Topel , Magnus Karlsson , Maciej Fijalkowski , Jonathan Lemon , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Christian Brauner , Richard Cochran , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , linux-fsdevel@vger.kernel.org, linux-perf-users@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, Oleg Nesterov , Jason Gunthorpe , John Hubbard , Jan Kara , "Kirill A . Shutemov" , Pavel Begunkov , Mika Penttila , Dave Chinner , Theodore Ts'o , Peter Xu , Paul McKenney References: <20230502111334.GP1597476@hirez.programming.kicks-ass.net> <20230502120810.GD1597538@hirez.programming.kicks-ass.net> <20230502124058.GB1597602@hirez.programming.kicks-ass.net> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230502124058.GB1597602@hirez.programming.kicks-ass.net> 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-Stat-Signature: 8deu683rfbrykgefyogx1uog5qenqmcd X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: B35DD4393D X-Rspam-User: X-HE-Tag: 1683032606-367683 X-HE-Meta: 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 yb9WVi0n pBugSU8OmpVTQEaYBdQcmwKjQ3SVsJ9w3vuAsHFdoqLFyQsJIgDdKkuLmgDo+mlj/4rPhR97HeGU0JK/RnnMHlUagNfoLWrp3Ctze1I7kow/r7SQy3w9yw20wg+3xuy0JM1dmgT+32iCnlFl5/4hl0K2QQYhNrLMyenDXuKR3zPQjWXyR1eoVIqcCPFkpCp95QQ255J2/oEf5m2nyH/F/UOa3VJSbtaViB2EEwPg7TQNcKQZWXVAZw7tjAg== 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 02.05.23 14:40, Peter Zijlstra wrote: > On Tue, May 02, 2023 at 02:08:10PM +0200, Peter Zijlstra wrote: > >>>> >>>> >>>> if (folio_test_anon(folio)) >>>> return true; >>> >>> This relies on the mapping so belongs below the lockdep assert imo. >> >> Oh, right you are. >> >>>> >>>> /* >>>> * Having IRQs disabled (as per GUP-fast) also inhibits RCU >>>> * grace periods from making progress, IOW. they imply >>>> * rcu_read_lock(). >>>> */ >>>> lockdep_assert_irqs_disabled(); >>>> >>>> /* >>>> * Inodes and thus address_space are RCU freed and thus safe to >>>> * access at this point. >>>> */ >>>> mapping = folio_mapping(folio); >>>> if (mapping && shmem_mapping(mapping)) >>>> return true; >>>> >>>> return false; >>>> >>>>> +} > > So arguably you should do *one* READ_ONCE() load of mapping and > consistently use that, this means open-coding both folio_test_anon() and > folio_mapping(). Open-coding folio_test_anon() should not be required. We only care about PAGE_MAPPING_FLAGS stored alongside folio->mapping, that will stick around until the anon page was freed. @Lorenzo, you might also want to special-case hugetlb directly using folio_test_hugetlb(). -- Thanks, David / dhildenb