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Wed, 13 Nov 2024 08:58:43 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id o8HTGkNqNGdaTgAAD6G6ig (envelope-from ); Wed, 13 Nov 2024 08:58:43 +0000 Message-ID: <54b8d0b9-a1c7-4c1b-a588-2e5308a977fb@suse.cz> Date: Wed, 13 Nov 2024 09:58:43 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/5] mm: make vma cache SLAB_TYPESAFE_BY_RCU To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: willy@infradead.org, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, mhocko@suse.com, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com References: <20241112194635.444146-1-surenb@google.com> <20241112194635.444146-5-surenb@google.com> Content-Language: en-US From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Stat-Signature: drk65kshysh6fii9qxeodo6zanchtonp X-Rspamd-Queue-Id: 8B8001C001A X-Rspamd-Server: rspam08 X-Rspam-User: X-HE-Tag: 1731488306-119791 X-HE-Meta: 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 A+HCufD6 TSsN0olRYAcF+qRi36FfnSFYoyskdqye04pO+1Iu4K8lr3Tl13jHhuDKGXdCZzQZ76EKd+liwNEl16IXvfv029sui5wMYgXBZeOYS/qJtnAO22y1nkcVgCWzYUNbvrbl/08T6X8vqZUAu9b+wKGeLnUX6h2bnSe7uyjpfgJvoSHVHDB9UC2ngu6WGYTcGTWgqEby5P/Oqpv3fs6V2OoRHl+KUx8P/TJHbDdpAETxB3D6XSn3CpxTrkHhULR06THOWQBxrDtNlK6c/2C7cx8OiYi2wXmmS1ok4phkn0GueVVohyHoz6Bkt5GfPglolP/cpYT4z5A7hVL2TjwUL+5bU/Dn8pg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000006, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/12/24 20:46, Suren Baghdasaryan wrote: > To enable SLAB_TYPESAFE_BY_RCU for vma cache we need to ensure that > object reuse before RCU grace period is over will be detected inside > lock_vma_under_rcu(). > lock_vma_under_rcu() enters RCU read section, finds the vma at the > given address, locks the vma and checks if it got detached or remapped > to cover a different address range. These last checks are there > to ensure that the vma was not modified after we found it but before > locking it. Vma reuse introduces a possibility that in between those > events of finding and locking the vma, it can get detached, reused, > added into a tree and be marked as attached. Current checks will help > detecting cases when: > - vma was reused but not yet added into the tree (detached check) > - vma was reused at a different address range (address check) > If vma is covering a new address range which still includes the address > we were looking for, it's not a problem unless the reused vma was added > into a different address space. Therefore checking that vma->vm_mm is > still the same is the the only missing check to detect vma reuse. Hi, I was wondering if we actually need the detached flag. Couldn't "detached" simply mean vma->vm_mm == NULL and we save 4 bytes? Do we ever need a vma that's detached but still has a mm pointer? I'd hope the places that set detached to false have the mm pointer around so it's not inconvenient.