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Tue, 10 Jun 2025 13:03:13 +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 HfYlBREtSGg5HQAAD6G6ig (envelope-from ); Tue, 10 Jun 2025 13:03:13 +0000 Message-ID: <83e262c2-419d-42cf-84db-b4ea2befbb72@suse.cz> Date: Tue, 10 Jun 2025 15:03:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/slab: fix folio_test_{anon,ksm}() false positive on slabs To: Harry Yoo Cc: rientjes@google.com, cl@gentwo.org, akpm@linux-foundation.org, roman.gushchin@linux.dev, willy@infradead.org, linux-mm@kvack.org References: <20250609132723.13118-1-harry.yoo@oracle.com> 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-Server: rspam06 X-Rspamd-Queue-Id: 28CC480016 X-Stat-Signature: z35n3howuk9q7xtwui59sdjaixemwxrp X-Rspam-User: X-HE-Tag: 1749560594-894219 X-HE-Meta: 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 ZOCfXDqG V1EeI1XXJ8FFARVcExgy6BGLv2F25vMhQiNivQrkuoNmXf78A/Cl8pwFK1Nlc42sus5fnb4Lat+QmLYGxLUt33yLgnSOpYX7Xl9whTuLADt7nRcAMuQnhiSsEe7tkI6u0SsywvwoAvVEoXlMpo5gxoOmTaS0z9+oxM/tOsqKX67LTHFTRhipJFqn7lfGL9KboA144B3LiqsnMIVW+EfcNARlOtssHbhOydgWcLiNSKA87R1T0KCAmDqrt2SCDF1m3omMbMegrEeZuRujfqQY8F7U3GXE89Ps2JJXfQcmJVAfs/TjJltcXUB2APcVUV5GnetH/5Zzo6Hnizms270OKS96cfRcfMR3lKtKc 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 6/10/25 14:38, Harry Yoo wrote: > On Mon, Jun 09, 2025 at 04:22:01PM +0200, Vlastimil Babka wrote: >> > With the change, the nonsense slab pages disappear: >> > >> > $ sudo ./page-types | grep slab >> > _______S___________________________________ slab >> > >> > Fixes: 130d4df57390 ("mm/sl[au]b: rearrange struct slab fields to allow larger rcu_head") >> > Signed-off-by: Harry Yoo >> > --- >> > >> > No Cc: stable because we don't usually check folio_test_anon() on slabs. >> >> Hmm maybe we could just make the code generating /proc/kpageflags stop >> testing/reporting those "flags" for slab pages? >> >> It could be even more future proof code for when struct slab is separated. > > Not sure if I follow. When struct slab is separated, checking if a memdesc > refers to slab or not will not have false positives, and thus no need for > "must check folio_test_slab() before checking folio_test_anon()" rule? Not sure I follow either. I mean today we can add code testing folio_test_slab() and only evaluating the mapping flags (ksm, anon) if it's not slab. Once we convert to memdescs, that code will stay logically the same even the testing functions will be named differently, no? > Of course, to fix false positive completely, I think we need to add > something like: > > __aligned(4) or __aligned(CONFIG_FUNCTION_ALIGNMENT) (whichever alignment is bigger) > > to rcu_free_slab(). OK. >> I mean there's even a comment above PAGE_MAPPING_ANON: >> >> * For slab pages, since slab reuses the bits in struct page to store its >> * internal states, the folio->mapping does not exist as such, nor do >> * these flags below. So in order to avoid testing non-existent bits, >> * please make sure that folio_test_slab(folio) actually evaluates to >> * false before calling the following functions (e.g., folio_test_anon). >> * See mm/slab.h. > > That comment was added because it was a hard lesson learned from > false positive. >