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Thu, 27 Nov 2025 09:05:39 +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 TiTwE2MUKGn5SwAAD6G6ig (envelope-from ); Thu, 27 Nov 2025 09:05:39 +0000 Message-ID: Date: Thu, 27 Nov 2025 10:05:38 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: fix vma_start_write_killable() signal handling To: Matthew Wilcox , Lorenzo Stoakes Cc: Andrew Morton , linux-mm@kvack.org, syzbot+5b19bad23ac7f44bf8b8@syzkaller.appspotmail.com, Suren Baghdasaryan , "Liam R. Howlett" References: <20251126174500.2498895-1-willy@infradead.org> Content-Language: en-US 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 6345B1C0012 X-Rspamd-Server: rspam06 X-Rspam-User: X-Stat-Signature: ty71176juy5uwyzq3rdymtgtgyyme9b8 X-HE-Tag: 1764234341-627735 X-HE-Meta: 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 H4kI2diw vmnEb/NyC5T5UdrLlZ43SmWD3BUpMG+vmPFkc1QEbgGjXWNEuTPMQFvWTSJgKTxD27rwyuVMFhR84ZbMCTdwsaTK9e3Bge3Jp3HMILwu4G7dpfD1ZkzkzZK91Pl/m1X111orClpaU61opUrFHbA7Mgbn5im+f+W0H72MJF5cqQ9F2jWSHRAlStFcO55DxiMtWsF39vDTIzmwHwYj4AXI4FCD8DaJQop2K2apUOdR1xZjMGhkGn6RMGnsi7N3Z91JDz3uW7mjT2ysySZFj7/UJ6LOYE2gzc5nQdZIsH6UR7pvABEfZhOyV4CpEwrrLzNfipxg97OMO6aHqVzWZGS9h/HNzmvKEiN7TSeOR4++cJmzGiCSC1YfscjFCp73yLMiQQrswXHoLPZtIcE6ouDPcnCF0qfD1DIRUXHSeC81W7wMR38I= 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 11/26/25 23:09, Matthew Wilcox wrote: > On Wed, Nov 26, 2025 at 08:33:47PM +0000, Lorenzo Stoakes wrote: >> if (refcount_sub_and_test(VMA_LOCK_OFFSET, &vma->vm_refcnt)) { >> /* >> * If the VMA is now detached which means we lost a race. >> * Let the caller know the VMA is detached. >> */ >> err = 0; >> } >> >> That gives a _lot_ more information, keeps it relatively top-level, doesn't >> make undue assumptions etc. > > Here's what I now have: > > if (err) { > if (refcount_sub_and_test(VMA_LOCK_OFFSET, &vma->vm_refcnt)) { > /* > * The wait failed, but the last reader went away > * as well. Tell the caller the VMA is detached. > */ > WARN_ON_ONCE(!detaching); > err = 0; > } Reviewed-by: Vlastimil Babka Thanks. > >> > Are you satisfied with the WARN_ON(!detaching)? >> > >> >> It'd be super weird to reach that code when not detaching so sure, think it >> should be VM_WARN_ON() though since the code would be horribly broken if >> that was not the case already no? > > The other places in this file are WARN_ON_ONCE rather than VM_WARN*, so > keep it consistent.