From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D1F52EEF30A for ; Thu, 5 Mar 2026 06:54:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 05E916B0089; Thu, 5 Mar 2026 01:54:24 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 00C326B008C; Thu, 5 Mar 2026 01:54:23 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E234F6B0092; Thu, 5 Mar 2026 01:54:23 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id CCB8C6B0089 for ; Thu, 5 Mar 2026 01:54:23 -0500 (EST) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 76A581608AE for ; Thu, 5 Mar 2026 06:54:23 +0000 (UTC) X-FDA: 84511095606.14.EBC2EA6 Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) by imf18.hostedemail.com (Postfix) with ESMTP id 0AC871C0014 for ; Thu, 5 Mar 2026 06:54:20 +0000 (UTC) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=ibm.com header.s=pp1 header.b=Lb8mSwG0; spf=pass (imf18.hostedemail.com: domain of venkat88@linux.ibm.com designates 148.163.158.5 as permitted sender) smtp.mailfrom=venkat88@linux.ibm.com; dmarc=pass (policy=none) header.from=ibm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1772693661; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=IqkJ2SnGytr5NhIc5m1uD9NLdn1cuaxB3p1uelmS6og=; b=fj+HTyOVopkRINSSOlHc30XWEL0/GaWuOJOhEwXDDVAPg9JyTLk4XnMd/l5u7dkzhSrDLG Yv6zcyrKrXYmvp1WqvGAFiFedhvCbLNWzy8bH2SI4nc/23fUb444yNFT8dyK9qmgz1tmb5 ouKV3KPlTPJrQO0H/YDiDSkuF+DNWaM= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=ibm.com header.s=pp1 header.b=Lb8mSwG0; spf=pass (imf18.hostedemail.com: domain of venkat88@linux.ibm.com designates 148.163.158.5 as permitted sender) smtp.mailfrom=venkat88@linux.ibm.com; dmarc=pass (policy=none) header.from=ibm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1772693661; a=rsa-sha256; cv=none; b=MxLUBz+RoEYpS4SACofux6fV0BjkiDNiCs+55fId2+KBjMzMtigh6O3wLe8PaO0uFgwary MzcNi6yuWn+jVCAEjnp/pUlbEZ5e57LwXt1AEkfd+bGsIsf0bbUSsjFrZoVaJT5MyOeaNV hnKkem1GQSKDs4nFPRDyMueP5zeXV5o= Received: from pps.filterd (m0353725.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 6254XZ632072521; Thu, 5 Mar 2026 06:54:16 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s=pp1; bh=IqkJ2S nGytr5NhIc5m1uD9NLdn1cuaxB3p1uelmS6og=; b=Lb8mSwG0hv/tOw4e4N0X15 t91VEISBErkjRnHriB0P9LSLmAxsaKrlVHW2Gs08AFEjPWNYm7een830K+D1ZC0P /1pT2C9zyPoTXonRw7QHSxMJsGphdEA9oWhMn0AoV4uwythI9Em5Tuip/glSxrfc RquTeEHQkZhaVoMylvKd/d9/VWG6PDg3pKOGgY/Z8BZWM8psodRtfk8Cztx/fSKE xAn+FcorZgYdtZ5So7JEksJYGhf6fjp/4nACcc8B5TUdHAeD/BZG/CMyZFFnsFvO 2C4gBxkXbNh4bt9IxG2sD/TcbXpAN+tTtzXe19zM7BVUf5Io8b1c7L/fQBiLJv7A == Received: from ppma11.dal12v.mail.ibm.com (db.9e.1632.ip4.static.sl-reverse.com [50.22.158.219]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4ckskc21h9-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 05 Mar 2026 06:54:15 +0000 (GMT) Received: from pps.filterd (ppma11.dal12v.mail.ibm.com [127.0.0.1]) by ppma11.dal12v.mail.ibm.com (8.18.1.2/8.18.1.2) with ESMTP id 6256m368008796; Thu, 5 Mar 2026 06:54:15 GMT Received: from smtprelay05.wdc07v.mail.ibm.com ([172.16.1.72]) by ppma11.dal12v.mail.ibm.com (PPS) with ESMTPS id 4cmdd1hpke-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 05 Mar 2026 06:54:15 +0000 Received: from smtpav06.dal12v.mail.ibm.com (smtpav06.dal12v.mail.ibm.com [10.241.53.105]) by smtprelay05.wdc07v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 6256sERl44171634 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 5 Mar 2026 06:54:14 GMT Received: from smtpav06.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id F09415805D; Thu, 5 Mar 2026 06:54:13 +0000 (GMT) Received: from smtpav06.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 81D5458060; Thu, 5 Mar 2026 06:54:09 +0000 (GMT) Received: from [9.61.242.165] (unknown [9.61.242.165]) by smtpav06.dal12v.mail.ibm.com (Postfix) with ESMTP; Thu, 5 Mar 2026 06:54:09 +0000 (GMT) Message-ID: <41f1c856-2c41-4d11-96e6-079d95d8efbb@linux.ibm.com> Date: Thu, 5 Mar 2026 12:24:08 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/slab: change stride type from unsigned short to unsigned int Content-Language: en-GB To: Harry Yoo , vbabka@suse.cz, akpm@linux-foundation.org Cc: cgroups@vger.kernel.org, cl@gentwo.org, hannes@cmpxchg.org, hao.li@linux.dev, linux-mm@kvack.org, mhocko@kernel.org, muchun.song@linux.dev, rientjes@google.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, surenb@google.com, pfalcato@suse.de References: <20260303135722.2680521-1-harry.yoo@oracle.com> From: Venkat Rao Bagalkote In-Reply-To: <20260303135722.2680521-1-harry.yoo@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: HFkeM0vPrecV2G65vZG5gISihM6chEbD X-Authority-Analysis: v=2.4 cv=b66/I9Gx c=1 sm=1 tr=0 ts=69a92898 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=yPCof4ZbAAAA:8 a=ZXp7wYQzh5jS1JEQpmwA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzA1MDA1MCBTYWx0ZWRfX+Z2K5HmLzXaC F02tV8z29yBlj5PhSJE5KfpeOnNmlb7i382qXDKASr1rjExM7TymMQtS3qjgrvS6HVIhXP81Eqw 5B+UqgBIkHqGf9OMkiImul/ibT/LxQS9g72Nvaeks+ASDGFU9HVxqDXFDEZZ12QA6L7KwyNyKDw ks2hdxYNhl3OT4YdaZAVzLxZWQryUr8FAe5u1z7mnQues1H0r+omsFymy8iwy+m/M4KlZlf+7kS ATh4+cK58Le6Qmb77BInOt7sV8MvPpqvWlXHjv+rNsrI+I4MFqPJkc2DNbLGIJTM/DAoZNJj202 lyZDja4znVtsk69Iudp5YnIxwpI2BgaoCUhKlpiZ0073s/FpWThJR7C+5l6evlJ8b7wPZShLPAh LVqd5LMjZQ0XO5PPqgAWXSG2AjLMcW/AxKV49anckXUOTit00TzjKFg5M7lbswWaVvY9RoUFCeQ lwZzMTbOQbjRFi2eo/Q== X-Proofpoint-GUID: 62c-SeErd2EMGGc8_z-jTovrtdJ-cWjz X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-05_01,2026-03-04_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 lowpriorityscore=0 phishscore=0 clxscore=1011 adultscore=0 bulkscore=0 impostorscore=0 malwarescore=0 spamscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2603050050 X-Rspamd-Queue-Id: 0AC871C0014 X-Stat-Signature: 4ywfeo5d3sxejsm48x8sy486nbrh8pk1 X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1772693660-167209 X-HE-Meta: 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 vWcdS/DG MkUwclf1cgSy/IFG0HQTz60GtxrbEPFXxYf5VczcDsTkp65kqVKbKmp+YpYRM6IQWluaugwxXBdtvuG0MGj+O7YqQHltzCOg1J91rWf9X85jnGizFhAaoTMz7W8V0debvuLeEHSmYStddIimEPJunTFrY/ujmbQIypMnqqdBc4rpJgGVVNjgiB8wjmkcIgNDVM1EeddD8+tVa11//1YMKntAx/ieqxFJvFyC0oEPRHtdF/VP9mX+s/4cOl4cyD0H3T0Snuf+TtpedFL99eBHvsD/e7AMNBh3hTSB7mnalU2Hj0Xvg5ipEyDvWGsxgYFbnyTfW5iYAugI5VeTu/zpdUpO6hFvCE4yPoyvyTTdTJHIQEW1/6ezuBr8g6cSYzisaQKg5HTNnqcE/0VM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 03/03/26 7:27 pm, Harry Yoo wrote: > Commit 7a8e71bc619d ("mm/slab: use stride to access slabobj_ext") > defined the type of slab->stride as unsigned short, because the author > initially planned to store stride within the lower 16 bits of the > page_type field, but later stored it in unused bits in the counters > field instead. > > However, the idea of having only 2-byte stride turned out to be a > serious mistake. On systems with 64k pages, order-1 pages are 128k, > which is larger than USHRT_MAX. It triggers a debug warning because > s->size is 128k while stride, truncated to 2 bytes, becomes zero: > > ------------[ cut here ]------------ > Warning! stride (0) != s->size (131072) > WARNING: mm/slub.c:2231 at alloc_slab_obj_exts_early.constprop.0+0x524/0x534, CPU#6: systemd-sysctl/307 > Modules linked in: > CPU: 6 UID: 0 PID: 307 Comm: systemd-sysctl Not tainted 7.0.0-rc1+ #6 PREEMPTLAZY > Hardware name: IBM,9009-22A POWER9 (architected) 0x4e0202 0xf000005 of:IBM,FW950.E0 (VL950_179) hv:phyp pSeries > NIP: c0000000008a9ac0 LR: c0000000008a9abc CTR: 0000000000000000 > REGS: c0000000141f7390 TRAP: 0700 Not tainted (7.0.0-rc1+) > MSR: 8000000000029033 CR: 28004400 XER: 00000005 > CFAR: c000000000279318 IRQMASK: 0 > GPR00: c0000000008a9abc c0000000141f7630 c00000000252a300 c00000001427b200 > GPR04: 0000000000000004 0000000000000000 c000000000278fd0 0000000000000000 > GPR08: fffffffffffe0000 0000000000000000 0000000000000000 0000000022004400 > GPR12: c000000000f644b0 c000000017ff8f00 0000000000000000 0000000000000000 > GPR16: 0000000000000000 c0000000141f7aa0 0000000000000000 c0000000141f7a88 > GPR20: 0000000000000000 0000000000400cc0 ffffffffffffffff c00000001427b180 > GPR24: 0000000000000004 00000000000c0cc0 c000000004e89a20 c00000005de90011 > GPR28: 0000000000010010 c00000005df00000 c000000006017f80 c00c000000177a00 > NIP [c0000000008a9ac0] alloc_slab_obj_exts_early.constprop.0+0x524/0x534 > LR [c0000000008a9abc] alloc_slab_obj_exts_early.constprop.0+0x520/0x534 > Call Trace: > [c0000000141f7630] [c0000000008a9abc] alloc_slab_obj_exts_early.constprop.0+0x520/0x534 (unreliable) > [c0000000141f76c0] [c0000000008aafbc] allocate_slab+0x154/0x94c > [c0000000141f7760] [c0000000008b41c0] refill_objects+0x124/0x16c > [c0000000141f77c0] [c0000000008b4be0] __pcs_replace_empty_main+0x2b0/0x444 > [c0000000141f7810] [c0000000008b9600] __kvmalloc_node_noprof+0x840/0x914 > [c0000000141f7900] [c000000000a3dd40] seq_read_iter+0x60c/0xb00 > [c0000000141f7a10] [c000000000b36b24] proc_reg_read_iter+0x154/0x1fc > [c0000000141f7a50] [c0000000009cee7c] vfs_read+0x39c/0x4e4 > [c0000000141f7b30] [c0000000009d0214] ksys_read+0x9c/0x180 > [c0000000141f7b90] [c00000000003a8d0] system_call_exception+0x1e0/0x4b0 > [c0000000141f7e50] [c00000000000d05c] system_call_vectored_common+0x15c/0x2ec > > This leads to slab_obj_ext() returning the first slabobj_ext or all > objects and confuses the reference counting of object cgroups [1] and > memory (un)charging for memory cgroups [2]. > > Fortunately, the counters field has 32 unused bits instead of 16 > on 64-bit CPUs, which is wide enough to hold any value of s->size. > Change the type to unsigned int. > > Reported-by: Venkat Rao Bagalkote > Closes: https://lore.kernel.org/lkml/ca241daa-e7e7-4604-a48d-de91ec9184a5@linux.ibm.com [1] > Closes: https://lore.kernel.org/all/ddff7c7d-c0c3-4780-808f-9a83268bbf0c@linux.ibm.com [2] > Fixes: 7a8e71bc619d ("mm/slab: use stride to access slabobj_ext") > Signed-off-by: Harry Yoo > --- > > Hi Venkat, could you please test this on top of 7.0-rc2 (instead of > 7.0-rc1) and see if the bugs [1] [2] are reproduced on your machine? Hello Harry, Apologizes for delayed response, I was out sick. I have tested this patch on top of 7.0-rc2, and confirm, this patch fixes both the reported issue. Tested-by: Venkat Rao Bagalkote Regards, Venkat. > > I reproduced a debug warning on a ppc machine and fixed it. > The bugs are expected to be resolved by this fix. > > p.s. After more debugging, I saw stride appeared as 0 even on the CPU > that wrote it, which likely rules out a memory ordering issue... > and I discovered this while decoding ppc assembly suspecting memory > corruption or a compiler bug, which came down to: > > "Hmm... why is the size truncated to 2 bytes?... OH WAIT!" > > mm/slab.h | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/mm/slab.h b/mm/slab.h > index f6ef862b60ef..e9ab292acd22 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -59,7 +59,7 @@ struct freelist_counters { > * to save memory. In case ->stride field is not available, > * such optimizations are disabled. > */ > - unsigned short stride; > + unsigned int stride; > #endif > }; > }; > @@ -559,20 +559,20 @@ static inline void put_slab_obj_exts(unsigned long obj_exts) > } > > #ifdef CONFIG_64BIT > -static inline void slab_set_stride(struct slab *slab, unsigned short stride) > +static inline void slab_set_stride(struct slab *slab, unsigned int stride) > { > slab->stride = stride; > } > -static inline unsigned short slab_get_stride(struct slab *slab) > +static inline unsigned int slab_get_stride(struct slab *slab) > { > return slab->stride; > } > #else > -static inline void slab_set_stride(struct slab *slab, unsigned short stride) > +static inline void slab_set_stride(struct slab *slab, unsigned int stride) > { > VM_WARN_ON_ONCE(stride != sizeof(struct slabobj_ext)); > } > -static inline unsigned short slab_get_stride(struct slab *slab) > +static inline unsigned int slab_get_stride(struct slab *slab) > { > return sizeof(struct slabobj_ext); > }