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Howlett" Cc: Bert Karwatzki , Andrew Morton , linux-mm@kvack.org Subject: Re: [PATCH v2 00/15] Avoid MAP_FIXED gap exposure Date: Thu, 27 Jun 2024 11:31:35 +0200 Message-ID: <20240627093138.11420-1-spasswolf@web.de> X-Mailer: git-send-email 2.45.2 In-Reply-To: nlq44eay3zjapg23tjprukm7w2ae6qcy5xtc5xsxogsmd52lwu@fhfzf4l6777u References: MIME-Version: 1.0 X-Provags-ID: V03:K1:xXwUcAdc5P8OTwCFC+MFxeo0NuNt0vS5M/eUZIdK9hDuKrymQAl nH121T314HrVmHfjMPDsR5Wh/ThYTPWXFSNIQE7yQ/SxbuzO2XV7C8IOp05p0wm4iqdokNL /odhelLkHraWJGIXNECZsZiZzLp//ebV9Bh1zpSUgu7rEkTVwSHUQNByaQ5rYE/RJ+vCUt/ 9sIEgW4/IsCa+GfkSlSoA== UI-OutboundReport: notjunk:1;M01:P0:S7st4eG4Sjg=;R1838Ek2BfPFusNTbbIO50nPr4S mG5bahg9OoDLwY6hdXWaMq12qLsgu5Q3fh6iC+ic7ZcfnpkgIl/nep7EXjbKBLufcuXmlk0hd tB4CCegVjlU11wgLq0Cs53ogvADO0mG62Cu+qC6vzQMWMDCFZms8Um+WYngy6vf3ILmdH2IKB t5z4XNgx00VZFSaCG+K+1MsLEUpuAxgQnBd4Sh8JbvSSShVdN+9ilSytzFWHuwFGDzj43lEaw 1gy1xLO2j4XJx5aZTtDc/eDPuqoaj52xXOJfMxt3+GjCsYBEBZdXAUFseyzfAoyXlUreN0S8w hGmH7/3BIkWB15p3An8RZ1TKGC6uB2FIv+MDKi8070IG/xJXty7Uj1ICYTjc/7+/UpTWk3MdF AUxRr3HW61/JGLy6Gz4bMmOsfxF0o7HTmE7QbVZ6K9V154JiRVNzrWo2i5djkIo+QIfRSrQwh ZnLXAk3E4dFb8b0v1bqzIhMeVd5GoagJWzlYFZPVFjasPjscinjHxOMxOpl2kMYxNbxlc6hCW xJherbgBWiJdWVDrxARpj7b6scsxW0rYrlZjBv5GgL4OtOJl/+TeYc4hArEKM1aBDmHZF9VzV f51GA/2c9KTiUT2Uhdy0RT65jNTKWhrT3WY3S15Q681fmHD4bAC14aWXpiZW4vhyTVzToQcbR l97AvhOYj973MEipTQyVR9Kxg2wdHORCYkb1cx5+bLt+WRKs8DXH91PNM2JqLZtC7PFtBUHY7 6L9/9K1OOhIDaMGWKU6VyY5KkuBUSQ3zpzwz6fZyTQ3F7vJLxwH2m7/sn6EEFviEtul0UCwmU tg8dbpRcjfg66hmrKa4jHBAHBdhwvTLLVj8CSa4SGxlsY= X-Stat-Signature: mizywfn5baaydf6uus1topecxzecpged X-Rspamd-Queue-Id: ECC44A001F X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1719480710-539527 X-HE-Meta: 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 WhNIb+Jb n2exjHj6UuCvxsAAqFcyxLab3qmTkDxCpKOxFnC7G9S2SOGHExbgH3PLz3O9Q8cP339JR+ZB5STp3x+BGEB/Y4vcpl6qDleysG+P/kaLyPshH0ksAyb8dHwRK3tAD1HB7nPAhZ+j0gemJ7m62FqzwAzwO7aF0nmxzna3gtZihxVTLNDpMIPGFRvPepF8Gc6gTY7cfX2g4ixfM8m/Zgkp02abgPzP0ZYTq8EVQWB/2gVaVzRYYiOjCccqUXNOwnBn/XEI27Bwu7D2MgW/R+zhoLeT2dDPosKYUTOW1QALUYPEXFZmI67uALzuhSMK+p6XgJiYzgTH0rl9MYzI= 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: * Andrew Morton [240626 16:59]: > 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? > If I understand this correctly the plan is to replace mmap_read_lock(mm) by rcu_read_lock(). So the consequences of a visible gap could be tested by replacing mmap_read_lock(mm) by rcu_read_lock() within the old code. If this is the case I'm willing to test it. Bert Karwatzki