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Wed, 15 Oct 2025 13:11:52 +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 IdTBAZid72gXOwAAD6G6ig (envelope-from ); Wed, 15 Oct 2025 13:11:52 +0000 Message-ID: <06b0c6fb-0123-4482-ac07-80f0faec3532@suse.cz> Date: Wed, 15 Oct 2025 15:11:51 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] slab: clear OBJEXTS_ALLOC_FAIL when freeing a slab Content-Language: en-US To: Hao Ge , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo Cc: Alexei Starovoitov , Shakeel Butt , Suren Baghdasaryan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hao Ge References: <20251015125945.481950-1-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: <20251015125945.481950-1-hao.ge@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: E018B8000C X-Rspamd-Server: rspam02 X-Stat-Signature: gbzewrtkhrwurywugopzigomqiwc4a5q X-HE-Tag: 1760533913-890485 X-HE-Meta: U2FsdGVkX19GYh/pZBAXQaaLDHvOswFkLUhw3kO8Fh9lDYYbDeSJWGQs/z/iAR5Qi+vf2Dv7KdcA86i/AamqSJffuFwiXhn0zecY8SCs3nBcOqSi+eEMH7dPKvxpig6mT5pRv0OdzYGYaDcJ1f7+aLjjSiTTykMbNLsLKTvCq1xA1PfWaRTNwoWX0vgEMHHARQE+C1OK9753KP1l0wlpszHDPvKWzYgWdiFkiY+s60AWS4ULabxdnoULS7Na/BHMBHlLto3lVdYIt7SAXXf0jF8Js3I3UMHsRaWnkoM7SL5bXUdJ1RSqsa9pE/Ad02SsdLL7B8E3EzFQLOqfPhdnPm3+uIB0HKbJXabCpG//2UyTt0sVAckrPOLgXSgryGI9rApTkoF3kJ1SAQpvJuAxsyE7W/y2SpDXUcV2qfRo3EjGU1JzH3f6ryxMzhW3eo2OvTaaA/y7fU6Te6MEHnKXJlibsGqXVyMEDPSK9iCc6cRM7jiIuQKEtix9RElm5flfLCu4qJyOqxPM39U+nvGKl0f5hTQ0/TRqUjortTBOkcdCULFCkA42AyLkvocv1WgxD9Cw2GRD4VlF7ieUu2te0ZJDFBlU/iW0Aum9yPz8BI4ndtG4EO0opmWmpPS2bfjMBDBaFMN0yAUFwG8bWxDx8oK+QGihqZo59fzbmZM5oBt3WGyyVy4gfvUT3AK8vFH/A9WslrV57+HhHZd+IJQHXOyNh0D4a6EVlfBB40wr86PQ5kRSDMvuD02O32P+/WqR1x5wIVyK7znluAswzd0/cXzXLJjzlbl2bg+GhZqmnpvd5TNvfIR4vgYSTIneN9FldB+hHPxmzDQznfvS0datfmX4xiRZB974H7wak/ka7xazK1+69O6p9NeA+k42dD+4OEdTh4xqR4B5ZM/fCAj+xtvyUgGOrAjpc5Knz4SOAsG64fvqcYxs3ZA7UNgujiLw770n/2S0cGj+KmKv0Ts FwFKpYTr UQYxfgbMUzwUCJscE/f8zAnMnJ3KF3qr+JfcbDgjztkWIwEIa/bg7s3MKGMWKcI35C5G5i8NkKha39E3YYz4lSgEqB0BtrxfWyQbEap+NeIoMFgdU86Bcy0/2x8/1ERTG5IUuJSywjwCoGPgSq0hRhsSGo246aBY92a/heKOHRtszHyDkYLhF5LKHCtAP5P3WiUcCzktFIzYdvvZBcqXCsR0VOcvZa6W472J7Iuq0jgH951na2VBzHP+SjZiw3DtZAvNstFsYyBaMEBaQKaGjYCisMfOnLpqMC+DAFSZ/hgs47KPmVHmNYaGxmPnoCx5tcATShIl1TdanB6HYfU4AbN2SnBy7rqiFveterWIJrPtdmVU5ij1RL85AwQ85iuTvnLKuahHIAs4Rjm7aaxbK9AdQRZSl3MPUNDYg 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 10/15/25 14:59, Hao Ge wrote: > From: Hao Ge > > If obj_exts allocation failed, slab->obj_exts is set to OBJEXTS_ALLOC_FAIL, > But we did not clear it when freeing the slab. Since OBJEXTS_ALLOC_FAIL and > MEMCG_DATA_OBJEXTS currently share the same bit position, during the > release of the associated folio, a VM_BUG_ON_FOLIO() check in > folio_memcg_kmem() is triggered because it was mistakenly assumed that > a valid folio->memcg_data was not cleared before freeing the folio. > > When freeing a slab, we clear slab->obj_exts if the obj_ext array has been > successfully allocated. So let's clear OBJEXTS_ALLOC_FAIL when freeing > a slab if the obj_ext array allocated fail to allow them to be returned > to the buddy system more smoothly. Thanks! > Fixes: 7612833192d5 ("slab: Reuse first bit for OBJEXTS_ALLOC_FAIL") > Suggested-by: Harry Yoo > Signed-off-by: Hao Ge > Reviewed-by: Suren Baghdasaryan > Acked-by: Shakeel Butt Since we changed the approach completely, I think we should not carry over the previously added review tags in this case. > --- > v4: Based on the discussion between Vlastimil and Harry, > modify the solution to clear OBJEXTS_ALLOC_FAIL when freeing a slab. > This does seem more reasonable. Thank you both. > --- > mm/slab.h | 26 ++++++++++++++++++++++++++ > mm/slub.c | 6 ++++++ > 2 files changed, 32 insertions(+) > > diff --git a/mm/slab.h b/mm/slab.h > index 078daecc7cf5..52424d6871bd 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -547,6 +547,28 @@ static inline struct slabobj_ext *slab_obj_exts(struct slab *slab) > return (struct slabobj_ext *)(obj_exts & ~OBJEXTS_FLAGS_MASK); > } > > +/* > + * objexts_clear_alloc_fail - Clear the OBJEXTS_ALLOC_FAIL for > + * the slab object extension vector associated with a slab. > + * @slab: a pointer to the slab struct > + */ > +static inline void objexts_clear_alloc_fail(struct slab *slab) > +{ > + unsigned long obj_exts = READ_ONCE(slab->obj_exts); > + > +#ifdef CONFIG_MEMCG > + /* > + * obj_exts should be either NULL, a valid pointer with > + * MEMCG_DATA_OBJEXTS bit set or be equal to OBJEXTS_ALLOC_FAIL. > + */ > + VM_BUG_ON_PAGE(obj_exts && !(obj_exts & MEMCG_DATA_OBJEXTS) && > + obj_exts != OBJEXTS_ALLOC_FAIL, slab_page(slab)); > + VM_BUG_ON_PAGE(obj_exts & MEMCG_DATA_KMEM, slab_page(slab)); > +#endif > + > + obj_exts &= ~OBJEXTS_ALLOC_FAIL; > + WRITE_ONCE(slab->obj_exts, obj_exts); > +} This is much larger than necessary I think. See below. > int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, > gfp_t gfp, bool new_slab); > > @@ -557,6 +579,10 @@ static inline struct slabobj_ext *slab_obj_exts(struct slab *slab) > return NULL; > } > > +static inline void objexts_clear_alloc_fail(struct slab *slab) > +{ > +} > + > #endif /* CONFIG_SLAB_OBJ_EXT */ > > static inline enum node_stat_item cache_vmstat_idx(struct kmem_cache *s) > diff --git a/mm/slub.c b/mm/slub.c > index b1f15598fbfd..80166a4a62f9 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2169,6 +2169,12 @@ static inline void free_slab_obj_exts(struct slab *slab) > { > struct slabobj_ext *obj_exts; > > + /* > + * If obj_exts allocation failed, slab->obj_exts is set to OBJEXTS_ALLOC_FAIL, > + * Therefore, we should clear the OBJEXTS_ALLOC_FAIL flag first when freeing a slab. > + */ > + objexts_clear_alloc_fail(slab); > + > obj_exts = slab_obj_exts(slab); > if (!obj_exts) > return; It should be enough that this return path does "slab->obj_exts = 0;" no?