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Mon, 26 Jan 2026 13:46:47 +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 f1wyC0dwd2mPagAAD6G6ig (envelope-from ); Mon, 26 Jan 2026 13:46:47 +0000 Message-ID: <795a4294-001f-4462-8afc-7310e9059943@suse.cz> Date: Mon, 26 Jan 2026 14:46:46 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2] mm/slab: avoid allocating slabobj_ext array from its own slab Content-Language: en-US To: Harry Yoo , akpm@linux-foundation.org Cc: 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: <20260126125714.88008-1-harry.yoo@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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Stat-Signature: sreqmegogibdchjpt5akx4m1mfawfg3u X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: C40924000D X-HE-Tag: 1769435208-513535 X-HE-Meta: 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 wnfW8Q2Y Ddj9Wc+kb82zRCsOF0fZUrD9qEvvs1/6lBDhAleMw3Nvn8zJsSKBzTzTKIdH1g7iqTMkafjVQtDtJDnA30dNOCLnzRsFr1y/qJ3Zt8Vo3uZtkaF5ua+qovGepEsUBqNM54dS3SMC3+aaugIgvspqLEtAICddLYaY80XCdKBUON8IOQiaMDG8pEEDqnqX3r2bN+ElLIgFUAqmA+FK5mZnPyF65t8O0xev/Wxth2xWf7iNpv9IM0uO6RKXDDOGYf0CNQBpKBugbOaX5Me/2rpWWhpFCsLmViUlG0zKwLbh2Zl/yGwkMe23/cMaxMam/1Q8aqkSPe0+3PVXzcUBFWh5zh5Cto677E7e55s8sbFuZppIZb6BARIrNthkiVgLA4G0RpmmsN/v3n2hqsstLUgYiL/ZFyw== 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 14:03, Harry Yoo wrote: > On Mon, Jan 26, 2026 at 09:57:14PM +0900, Harry Yoo wrote: >> When allocating slabobj_ext array in alloc_slab_obj_exts(), the array >> can be allocated from the same slab we're allocating the array for. >> This led to obj_exts_in_slab() incorrectly returning true [1], >> although the array is not allocated from wasted space of the slab. >> >> Vlastimil Babka observed that this problem should be fixed even when >> ignoring its incompatibility with obj_exts_in_slab(), because it creates >> slabs that are never freed as there is always at least one allocated >> object. >> >> To avoid this, use the next kmalloc size or large kmalloc when >> the array can be allocated from the same cache we're allocating >> the array for. >> >> In case of random kmalloc caches, there are multiple kmalloc caches >> for the same size and the cache is selected based on the caller address. >> Because it is fragile to ensure the same caller address is passed to >> kmalloc_slab(), kmalloc_noprof(), and kmalloc_node_noprof(), bump the >> size to (s->object_size + 1) when the sizes are equal, instead of >> directly comparing the kmem_cache pointers. >> >> Note that this doesn't happen when memory allocation profiling is >> disabled, as when the allocation of the array is triggered by memory >> cgroup (KMALLOC_CGROUP), the array is allocated from KMALLOC_NORMAL. >> >> Reported-by: kernel test robot >> Closes: https://lore.kernel.org/oe-lkp/202601231457.f7b31e09-lkp@intel.com [1] >> Cc: stable@vger.kernel.org >> Fixes: 4b8736964640 ("mm/slab: add allocation accounting into slab allocation and free paths") >> Signed-off-by: Harry Yoo >> --- >> >> V1 -> V2: >> - Simplified implementation based on Vlastimil's comment >> - added virt_to_slab() != NULL check before dereferencing it - because >> (in theory) it may be allocated via large kmalloc. >> >> mm/slub.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++------- >> 1 file changed, 53 insertions(+), 7 deletions(-) >> >> diff --git a/mm/slub.c b/mm/slub.c >> index f21b2f0c6f5a..5b4a3b9b7826 100644 >> --- a/mm/slub.c >> +++ b/mm/slub.c >> @@ -2095,6 +2095,49 @@ static inline void init_slab_obj_exts(struct slab *slab) >> slab->obj_exts = 0; >> } >> >> +/* >> + * 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 cache 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 >> + * may 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; > > Hmm maybe we don't need this as there's !is_kmalloc_normal(s) check, > but this allows optimizing out the checks below when > CONFIG_MEM_ALLOC_PROFILING is not enabled. > > So probably worth keeping it. Right. Thanks, added to slab/for-next as the first commit of the obj_metadata branch.