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Fri, 26 Sep 2025 12:25:54 +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 35hXGlKG1mgnRAAAD6G6ig (envelope-from ); Fri, 26 Sep 2025 12:25:54 +0000 Message-ID: <7a3406c6-93da-42ee-a215-96ac0213fd4a@suse.cz> Date: Fri, 26 Sep 2025 14:25:54 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [linux-next:master] [slab] db93cdd664: BUG:kernel_NULL_pointer_dereference,address To: Alexei Starovoitov , Suren Baghdasaryan Cc: kernel test robot , Alexei Starovoitov , Harry Yoo , oe-lkp@lists.linux.dev, kbuild test robot , kasan-dev , "open list:CONTROL GROUP (CGROUP)" , linux-mm References: <202509171214.912d5ac-lkp@intel.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: 8bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 554BA40005 X-Stat-Signature: wdqzxfp4yw8saymzhejqj38nekmstnb7 X-HE-Tag: 1758889557-784576 X-HE-Meta: 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 zmm7dpSt lz44uBxZZpCpSRSe9hB2dbn3tvmeh+q42f2EwDW7ps0v3iGyyoWIpYiGzkbTuJJR88aMhM7KHOGzihI/DtXkFQFsb7eI55sPO9JMDLXkn8FpffTcOQfrTR0nlBPxAJa0hHwU8voO7cqJ9blzvNsxUA4mN3z1UIOB7zD87ARqFh6K/lxkC8vOePBG29VZubS5ProaamruM+65QfD/EgYZ1RJ/9UCrCCClbDORgerlAurOVSHOjm8dwJBIK55ekLsmyYIVTXCWaLkw01sUHL3hhLDRwHTi4FEnnk/mNDE8QgMv3HVToWm3Oisom46HAE/0QyNV1FTXxK8F9z//pMRKyNZFwjDtwUqdImKsZpGhFsMgnwV+NsQILgVKY/flABc5Vv+CekpSEMDoz9mZFYsnaRGQOgYLBoyz0sC/CAgxjorl1vaNt99+6YPus2hGKam+UIAIh6kdO3cfMvy4= 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 9/19/25 20:31, Alexei Starovoitov wrote: > On Fri, Sep 19, 2025 at 8:01 AM Suren Baghdasaryan wrote: >> >> > >> > I would not. I think adding 'boot or not' logic to these two >> > will muddy the waters and will make the whole slab/page_alloc/memcg >> > logic and dependencies between them much harder to follow. >> > I'd either add a comment to alloc_slab_obj_exts() explaining >> > what may happen or add 'boot or not' check only there. >> > imo this is a niche, rare and special. >> >> Ok, comment it is then. >> Will you be sending a new version or Vlastimil will be including that >> in his fixup? > > Whichever way. I can, but so far Vlastimil phrasing of comments > were much better than mine :) So I think he can fold what he prefers. I'm adding this. Hopefully we'll be able to make sheaves the only percpu caching layer in SLUB in the (near) future, and then requirement for cmpxchg16b for allocations will be gone. diff --git a/mm/slub.c b/mm/slub.c index 9f1054f0b9ca..f9f7f3942074 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2089,6 +2089,13 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, gfp &= ~OBJCGS_CLEAR_MASK; /* Prevent recursive extension vector allocation */ gfp |= __GFP_NO_OBJ_EXT; + + /* + * Note that allow_spin may be false during early boot and its + * restricted GFP_BOOT_MASK. Due to kmalloc_nolock() only supporting + * architectures with cmpxchg16b, early obj_exts will be missing for + * very early allocations on those. + */ if (unlikely(!allow_spin)) { size_t sz = objects * sizeof(struct slabobj_ext);