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Howlett" Cc: linux-mm@kvack.org, Suren Baghdasaryan , Vlastimil Babka , Lorenzo Stoakes , Matthew Wilcox , sidhartha.kumar@oracle.com, "Paul E . McKenney" , Bert Karwatzki , Jiri Olsa , linux-kernel@vger.kernel.org, Kees Cook Subject: Re: [PATCH v2 00/15] Avoid MAP_FIXED gap exposure Message-Id: <20240626135855.a4b64612a9104ff163e30bd7@linux-foundation.org> In-Reply-To: <20240625191145.3382793-1-Liam.Howlett@oracle.com> References: <20240625191145.3382793-1-Liam.Howlett@oracle.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: D20BF8002A X-Stat-Signature: xwjgq3pk1yiczxfwd14zikufh73ojwbz X-Rspam-User: X-HE-Tag: 1719435537-767505 X-HE-Meta: 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 tReZakpI F+l6TyLAqVRtUw6Y/2t59da4u8yD8az1nSDrilzAjGQ+OTsEJYe0c6OGBTBJTpoVsTg9JO/miGedBwBbRIV0VZjuDd2DmvfJIF5IaTY3eBSuBb1LHKv37EL27ZKT7HiNlxAz1HK4XobJ91a47qfNWjVqpVnHJeP9cgUrML1mshx4a8CLHZU1L84iSybX6dgWD+BMNMEn0RlQwkclghsf36OMy4NWRGCHGCbB9TzzNIT08KyA81loyK6YOd+w6xZGRGVVu8h0kxkrEcI4UJsvndwu+5A0Yoe+XZ3R4plChz2PkWng= 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: List-Subscribe: List-Unsubscribe: On Tue, 25 Jun 2024 15:11:30 -0400 "Liam R. Howlett" wrote: > It is now possible to walk the vma tree using the rcu read locks and is > beneficial to do so to reduce lock contention. Doing so while a > MAP_FIXED mapping is executing means that a reader may see a gap in the > vma tree that should never logically exist - and does not when using the > mmap lock in read mode. The temporal gap exists because mmap_region() > calls munmap() prior to installing the new mapping. What are the consequences when this race hits? IOW, why do we need to change anything?