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Fri, 20 Jun 2025 15:02:41 +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 kKzFORF4VWjMVwAAD6G6ig (envelope-from ); Fri, 20 Jun 2025 15:02:41 +0000 Message-ID: Date: Fri, 20 Jun 2025 17:02:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 5/5] mm/madvise: eliminate very confusing manipulation of prev VMA Content-Language: en-US To: Lorenzo Stoakes , Andrew Morton Cc: David Hildenbrand , Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Jann Horn , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Lance Yang , SeongJae Park , Suren Baghdasaryan References: <441f6b68c62bff6aff68bd1befe90ffc1576b56f.1750363557.git.lorenzo.stoakes@oracle.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: <441f6b68c62bff6aff68bd1befe90ffc1576b56f.1750363557.git.lorenzo.stoakes@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: kaq9ernnpq7o1csoh6qtznwtgtcnwppi X-Rspamd-Queue-Id: 977691C000B X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1750431764-990187 X-HE-Meta: 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 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 6/19/25 22:26, Lorenzo Stoakes wrote: > The madvise code has for the longest time had very confusing code around > the 'prev' VMA pointer passed around various functions which, in all cases > except madvise_update_vma(), is unused and instead simply updated as soon > as the function is invoked. > > To compound the confusion, the prev pointer is also used to indicate to the > caller that the mmap lock has been dropped and that we can therefore not > safely access the end of the current VMA (which might have been updated by > madvise_update_vma()). > > Clear up this confusion by not setting prev = vma anywhere except in > madvise_walk_vmas(), update all references to prev which will always be > equal to vma after madvise_vma_behavior() is invoked, and adding a flag to > indicate that the lock has been dropped to make this explicit. > > Additionally, drop a redundant BUG_ON() from madvise_collapse(), which is > simply reiterating the BUG_ON(mmap_locked) above it (note that BUG_ON() is > not appropriate here, but we leave existing code as-is). > > We finally adjust the madvise_walk_vmas() logic to be a little clearer - > delaying the assignment of the end of the range to the start of the new > range until the last moment and handling the lock being dropped scenario > immediately. > > Additionally add some explanatory comments. > > Signed-off-by: Lorenzo Stoakes Reviewed-by: Vlastimil Babka Much nicer now, thanks!