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Commit7a8e71bc61("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 <SF,EE,ME,IR,DR,RI,LE> 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 <venkat88@linux.ibm.com> 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:7a8e71bc61("mm/slab: use stride to access slabobj_ext") Signed-off-by: Harry Yoo <harry.yoo@oracle.com> Link: https://patch.msgid.link/20260303135722.2680521-1-harry.yoo@oracle.com Reviewed-by: Hao Li <hao.li@linux.dev> Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com> Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst
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