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Tue, 14 Oct 2025 20:58:26 +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 PYpSAnK57mh9cAAAD6G6ig (envelope-from ); Tue, 14 Oct 2025 20:58:26 +0000 Message-ID: Date: Tue, 14 Oct 2025 22:58:25 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] slab: Add check for memcg_data != OBJEXTS_ALLOC_FAIL in folio_memcg_kmem Content-Language: en-US To: Shakeel Butt , Suren Baghdasaryan Cc: Hao Ge , Alexei Starovoitov , Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Harry Yoo , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hao Ge , David Hildenbrand References: <20251014152751.499376-1-hao.ge@linux.dev> 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-Rspam-User: X-Stat-Signature: 9txjnkt5a6mujqrjq98wdmboft119uqc X-Rspamd-Queue-Id: 2031B140004 X-Rspamd-Server: rspam09 X-HE-Tag: 1760475507-855932 X-HE-Meta: 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 s3ZoatjX peA3D4MkPwqo61Gqwk4+uJEmbDizSgseYgTZ8oeXnPHsbaqOd2sU6rHhGMKXLLMy7oj8zg7xy/E2igUnZjeCIpAafddAjaM2TjCQSXzxq0vvB/w5ax4sQsHAkxrmwD65RP+bbu4t20HziJnhnfvArp+at5HaGd2hniDN7e1lCUGz18OE63xvcBMBrdmv+kQF+GJz3cso8e/E6rTv+Qpq2qbI4woMcJf+a8O5l1WZVyC+sN/lBAh0jPPbWTaqe1fb4N4zYZFk6SwzRgHiLiWbr08r0hnorHlQF+rbE+IjN978vGGwMUdmab37IZ87v2A7vWVV8WGNqYjUx6p20OCK7Tc7Zu+S3T7rD+XEND5mkjDkv5R2iFhrdXAKKzo1oc9LRxMhmnwWuiqUo77wmQFvQ7cEz+3jNvkADXC83UD3smTuvRYpazpTvlG/TLAMnVLArBhyg9GDYBo3+VhZF8Uyh86lkMQ== 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 10/14/25 22:14, Shakeel Butt wrote: > On Tue, Oct 14, 2025 at 09:12:43AM -0700, Suren Baghdasaryan wrote: >> On Tue, Oct 14, 2025 at 8:28 AM Hao Ge wrote: >> > >> > From: Hao Ge >> > >> > Since OBJEXTS_ALLOC_FAIL and MEMCG_DATA_OBJEXTS currently share >> > the same bit position, we cannot determine whether memcg_data still >> > points to the slabobj_ext vector simply by checking >> > folio->memcg_data & MEMCG_DATA_OBJEXTS. >> > >> > If obj_exts allocation failed, slab->obj_exts is set to OBJEXTS_ALLOC_FAIL, >> > and during the release of the associated folio, the BUG check is triggered >> > because it was mistakenly assumed that a valid folio->memcg_data >> > was not cleared before freeing the folio. >> > >> > So let's check for memcg_data != OBJEXTS_ALLOC_FAIL in folio_memcg_kmem. >> > >> > Fixes: 7612833192d5 ("slab: Reuse first bit for OBJEXTS_ALLOC_FAIL") >> > Suggested-by: Harry Yoo >> > Signed-off-by: Hao Ge >> >> Reviewed-by: Suren Baghdasaryan >> >> nit: I think it would be helpful if the changelog explained why we >> need the additional check. We can have the same bit set in two >> different situations: >> 1. object extension vector allocation failure; >> 2. memcg_data pointing to a valid mem_cgroup. >> To distinguish between them, we need to check not only the bit itself >> but also the rest of this field. If the rest is NULL, we have case 1, >> otherwise case 2. > > With Suren's suggestion, you can add: > > Acked-by: Shakeel Butt Thanks, I added Suren's suggestion and pushed to slab/for-next-fixes: https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab.git/commit/?h=slab/for-next-fixes&id=711c435c89e59ee32bf8bb1c0d875a07931da5a8 Resisted the impulse to change the single VM_BUG_ON_FOLIO to VM_WARN_ON_ONCE_FOLIO because we're still going to do that systematically, right?