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Mon, 26 Jan 2026 08:37:29 +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 G8kKMsknd2lbJQAAD6G6ig (envelope-from ); Mon, 26 Jan 2026 08:37:29 +0000 Message-ID: <55ab1a9b-1d7a-4e7e-b6bc-ee327197dc4b@suse.cz> Date: Mon, 26 Jan 2026 09:37:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/slab: avoid allocating slabobj_ext array from its own slab Content-Language: en-US To: Harry Yoo Cc: akpm@linux-foundation.org, linux-mm@kvack.org, cl@gentwo.org, rientjes@google.com, surenb@google.com, hao.li@linux.dev, kernel test robot , stable@vger.kernel.org References: <20260124104614.9739-1-harry.yoo@oracle.com> <2b116198-b27a-4b20-90b2-951343f9fff1@suse.cz> 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-Stat-Signature: i6955jqju335ywn1uocgw5xyffihbmyj X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 043581C0005 X-HE-Tag: 1769416651-437096 X-HE-Meta: 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 eVGz8oOI AbFwE9+qpsO7XveF273UnmudaEaUVoWHeaRiI5gCYE1nnpJLrE6sT7QLdGZy722rzb+8/6/IWBSytqZJnM11qNaArKA+dr+TWf+9OiB6K6fYCGnrKo6k+cLUuXewpBhgsSACRQ7dh13brgq26w5YHRUlNvDkGwz5bw/ADzRmukkm5FAahyX5/cpQicJzvU7v/kOtXNsKnzVh/AySViDZxfCTEYkZ5WcbSC0UlWTJmxL+sW4h9E6OKKCY/nMKlh2OrwoXXDcuc6ydrSZygepIc7hfC6JbKPVh2FEt1Cd1w708U9gAKHfNR+0wHjtQ/IGW9lz1WGJt8GStUEI0= 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 1/26/26 09:30, Harry Yoo wrote: > On Mon, Jan 26, 2026 at 08:36:16AM +0100, Vlastimil Babka wrote: > /* > * Calculate the allocation size for slabobj_ext array. > * > * When memory allocation profiling is enabled, the obj_exts array > * could be allocated from the same slab it's being allocated for. > * This would prevent the slab from ever being freed because it would > * always contain at least one allocated object (its own obj_exts array). > * > * To avoid this, increase the allocation size when we detect the array > * would come from the same cache, forcing it to use a different cache. > */ > static inline size_t obj_exts_alloc_size(struct kmem_cache *s, > struct slab *slab, gfp_t gfp) > { > size_t sz = sizeof(struct slabobj_ext) * slab->objects; > struct kmem_cache *obj_exts_cache; > > /* > * slabobj_ext array for KMALLOC_CGROUP allocations > * are served from KMALLOC_NORMAL caches. > */ > if (!mem_alloc_profiling_enabled()) > return sz; > > if (sz > KMALLOC_MAX_CACHE_SIZE) > return sz; > > if (!is_kmalloc_normal(s)) > return sz; > > obj_exts_cache = kmalloc_slab(sz, NULL, gfp, 0); > /* > * Random kmalloc caches have multiple caches per size, and the cache Maybe start with something like "We can't simply compare s with obj_exts_cache, because..." > * is selected by the caller address. Since caller address may differ > * between kmalloc_slab() and actual allocation, bump size when both > * are normal kmalloc caches of same size. As we don't test the other for normal kmalloc(), anymore this now reads as if we forgot to. > */ > if (s->size == obj_exts_cache->size) > return s->object_size + 1; Why switch to size from object_size for the checks? I'd be worried that due to debugging etc this can yield wrong results? > > return sz; > } >