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Thu, 18 Sep 2025 07:06:40 +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 NWI5AICvy2hLKAAAD6G6ig (envelope-from ); Thu, 18 Sep 2025 07:06:40 +0000 Message-ID: Date: Thu, 18 Sep 2025 09:06:39 +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 Cc: kernel test robot , Alexei Starovoitov , Harry Yoo , Suren Baghdasaryan , 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-Rspamd-Action: no action X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: E02272000A X-Stat-Signature: 55kqs3qf4yuysmibgdeiy5g7ga598hsk X-Rspam-User: X-HE-Tag: 1758179201-753944 X-HE-Meta: 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 UXeRDjbv qEwvWHpUjjoGtWEF32TD28BC/0WOgpIDb/0RRW2IbVFSXfvIfgpBYL08n/lP9GbX5U1TUGZkEGYLTqffIDODeFsOtqIwRD6Zvg79JplcfZSqSDa5yxzpIoRmgXq5Q5ADlIXvIoeQJozgc17zc2zNONDn8F9NmC0ZhrhRf1UgwahcTe/vBEvH8vNhWOZ2GDIhrRFniQtC/Xz4kQY/RPYeqdd9t36MJdoIaOc2nKXrqL/tVmCIPuVatY+sUyAA3Cp1PmX3ZTbaUu4ADuef5ZJjhLn8NESH+LTBw8gsW864j98eHn02yiHJY0fuxv/GL6wecCAkxvEUH+K/x+OyHjU9oasF9zp6YOaruahXFkf7i1SKas7iT8f4o9EeGJbHJIXKgySeGr7q4SSOY/tU= 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 9/17/25 20:38, Alexei Starovoitov wrote: > On Wed, Sep 17, 2025 at 2:18 AM Vlastimil Babka wrote: >> >> Also I was curious to find out which path is triggered so I've put a >> dump_stack() before the kmalloc_nolock call: >> >> [ 0.731812][ T0] Call Trace: >> [ 0.732406][ T0] __dump_stack+0x18/0x30 >> [ 0.733200][ T0] dump_stack_lvl+0x32/0x90 >> [ 0.734037][ T0] dump_stack+0xd/0x20 >> [ 0.734780][ T0] alloc_slab_obj_exts+0x181/0x1f0 >> [ 0.735862][ T0] __alloc_tagging_slab_alloc_hook+0xd1/0x330 >> [ 0.736988][ T0] ? __slab_alloc+0x4e/0x70 >> [ 0.737858][ T0] ? __set_page_owner+0x167/0x280 >> [ 0.738774][ T0] __kmalloc_cache_noprof+0x379/0x460 >> [ 0.739756][ T0] ? depot_fetch_stack+0x164/0x180 >> [ 0.740687][ T0] ? __set_page_owner+0x167/0x280 >> [ 0.741604][ T0] __set_page_owner+0x167/0x280 >> [ 0.742503][ T0] post_alloc_hook+0x17a/0x200 >> [ 0.743404][ T0] get_page_from_freelist+0x13b3/0x16b0 >> [ 0.744427][ T0] ? kvm_sched_clock_read+0xd/0x20 >> [ 0.745358][ T0] ? kvm_sched_clock_read+0xd/0x20 >> [ 0.746290][ T0] ? __next_zones_zonelist+0x26/0x60 >> [ 0.747265][ T0] __alloc_frozen_pages_noprof+0x143/0x1080 >> [ 0.748358][ T0] ? lock_acquire+0x8b/0x180 >> [ 0.749209][ T0] ? pcpu_alloc_noprof+0x181/0x800 >> [ 0.750198][ T0] ? sched_clock_noinstr+0x8/0x10 >> [ 0.751119][ T0] ? local_clock_noinstr+0x137/0x140 >> [ 0.752089][ T0] ? kvm_sched_clock_read+0xd/0x20 >> [ 0.753023][ T0] alloc_slab_page+0xda/0x150 >> [ 0.753879][ T0] new_slab+0xe1/0x500 >> [ 0.754615][ T0] ? kvm_sched_clock_read+0xd/0x20 >> [ 0.755577][ T0] ___slab_alloc+0xd79/0x1680 >> [ 0.756469][ T0] ? pcpu_alloc_noprof+0x538/0x800 >> [ 0.757408][ T0] ? __mutex_unlock_slowpath+0x195/0x3e0 >> [ 0.758446][ T0] __slab_alloc+0x4e/0x70 >> [ 0.759237][ T0] ? mm_alloc+0x38/0x80 >> [ 0.759993][ T0] kmem_cache_alloc_noprof+0x1db/0x470 >> [ 0.760993][ T0] ? mm_alloc+0x38/0x80 >> [ 0.761745][ T0] ? mm_alloc+0x38/0x80 >> [ 0.762506][ T0] mm_alloc+0x38/0x80 >> [ 0.763260][ T0] poking_init+0xe/0x80 >> [ 0.764032][ T0] start_kernel+0x16b/0x470 >> [ 0.764858][ T0] i386_start_kernel+0xce/0xf0 >> [ 0.765723][ T0] startup_32_smp+0x151/0x160 >> >> And the reason is we still have restricted gfp_allowed_mask at this point: >> /* The GFP flags allowed during early boot */ >> #define GFP_BOOT_MASK (__GFP_BITS_MASK & ~(__GFP_RECLAIM|__GFP_IO|__GFP_FS)) >> >> It's only lifted to a full allowed mask later in the boot. > > Ohh. That's interesting. > >> That means due to "kmalloc_nolock() is not supported on architectures that >> don't implement cmpxchg16b" such architectures will no longer get objexts >> allocated in early boot. I guess that's not a big deal. >> >> Also any later allocation having its flags screwed for some reason to not >> have __GFP_RECLAIM will also lose its objexts. Hope that's also acceptable. >> I don't know if we can distinguish a real kmalloc_nolock() scope in >> alloc_slab_obj_exts() without inventing new gfp flags or passing an extra >> argument through several layers of functions. > > I think it's ok-ish. > Can we add a check to alloc_slab_obj_exts() that sets allow_spin=true > if we're in the boot phase? Like: > if (gfp_allowed_mask != __GFP_BITS_MASK) > allow_spin = true; > or some cleaner way to detect boot time by checking slab_state ? > bpf is not active during the boot and nothing should be > calling kmalloc_nolock. Checking the gfp_allowed_mask should work. Slab state is already UP so won't help, and this is not really about slab state anyway. But whether worth it... Suren what do you think?