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With PREEMPT_RT as potential configuration option, spinlock_t is now considered as a sleeping lock, and thus might cause issues when used in an atomic context. But even with PREEMPT_RT as potential configuration option, raw_spinlock_t remains as a true spinning lock/atomic context. This creates potential issues with the s390 debug/tracing feature. The functions to trace errors are called in various contexts, including under lock of raw_spinlock_t, and thus the used spinlock_t in each debug area is in violation of the locking semantics. Here are two examples involving failing PCI Read accesses that are traced while holding `pci_lock` in `drivers/pci/access.c`: ============================= [ BUG: Invalid wait context ] 6.19.0-devel #18 Not tainted ----------------------------- bash/3833 is trying to lock: 0000027790baee30 (&rc->lock){-.-.}-{3:3}, at: debug_event_common+0xfc/0x300 other info that might help us debug this: context-{5:5} 5 locks held by bash/3833: #0: 0000027efbb29450 (sb_writers#3){.+.+}-{0:0}, at: ksys_write+0x7c/0xf0 #1: 00000277f0504a90 (&of->mutex#2){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x13e/0x260 #2: 00000277beed8c18 (kn->active#339){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x164/0x260 #3: 00000277e9859190 (&dev->mutex){....}-{4:4}, at: pci_dev_lock+0x2e/0x40 #4: 00000383068a7708 (pci_lock){....}-{2:2}, at: pci_bus_read_config_dword+0x4a/0xb0 stack backtrace: CPU: 6 UID: 0 PID: 3833 Comm: bash Kdump: loaded Not tainted 6.19.0-devel #18 PREEMPTLAZY Hardware name: IBM 9175 ME1 701 (LPAR) Call Trace: [<00000383048afec2>] dump_stack_lvl+0xa2/0xe8 [<00000383049ba166>] __lock_acquire+0x816/0x1660 [<00000383049bb1fa>] lock_acquire+0x24a/0x370 [<00000383059e3860>] _raw_spin_lock_irqsave+0x70/0xc0 [<00000383048bbb6c>] debug_event_common+0xfc/0x300 [<0000038304900b0a>] __zpci_load+0x17a/0x1f0 [<00000383048fad88>] pci_read+0x88/0xd0 [<00000383054cbce0>] pci_bus_read_config_dword+0x70/0xb0 [<00000383054d55e4>] pci_dev_wait+0x174/0x290 [<00000383054d5a3e>] __pci_reset_function_locked+0xfe/0x170 [<00000383054d9b30>] pci_reset_function+0xd0/0x100 [<00000383054ee21a>] reset_store+0x5a/0x80 [<0000038304e98758>] kernfs_fop_write_iter+0x1e8/0x260 [<0000038304d995da>] new_sync_write+0x13a/0x180 [<0000038304d9c5d0>] vfs_write+0x200/0x330 [<0000038304d9c88c>] ksys_write+0x7c/0xf0 [<00000383059cfa80>] __do_syscall+0x210/0x500 [<00000383059e4c06>] system_call+0x6e/0x90 INFO: lockdep is turned off. ============================= [ BUG: Invalid wait context ] 6.19.0-devel #3 Not tainted ----------------------------- bash/6861 is trying to lock: 0000009da05c7430 (&rc->lock){-.-.}-{3:3}, at: debug_event_common+0xfc/0x300 other info that might help us debug this: context-{5:5} 5 locks held by bash/6861: #0: 000000acff404450 (sb_writers#3){.+.+}-{0:0}, at: ksys_write+0x7c/0xf0 #1: 000000acff41c490 (&of->mutex#2){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x13e/0x260 #2: 0000009da36937d8 (kn->active#75){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x164/0x260 #3: 0000009dd15250d0 (&zdev->state_lock){+.+.}-{4:4}, at: enable_slot+0x2e/0xc0 #4: 000001a19682f708 (pci_lock){....}-{2:2}, at: pci_bus_read_config_byte+0x42/0xa0 stack backtrace: CPU: 16 UID: 0 PID: 6861 Comm: bash Kdump: loaded Not tainted 6.19.0-devel #3 PREEMPTLAZY Hardware name: IBM 9175 ME1 701 (LPAR) Call Trace: [<000001a194837ec2>] dump_stack_lvl+0xa2/0xe8 [<000001a194942166>] __lock_acquire+0x816/0x1660 [<000001a1949431fa>] lock_acquire+0x24a/0x370 [<000001a19596b810>] _raw_spin_lock_irqsave+0x70/0xc0 [<000001a194843b6c>] debug_event_common+0xfc/0x300 [<000001a194888b0a>] __zpci_load+0x17a/0x1f0 [<000001a194882d88>] pci_read+0x88/0xd0 [<000001a195453b88>] pci_bus_read_config_byte+0x68/0xa0 [<000001a195457bc2>] pci_setup_device+0x62/0xad0 [<000001a195458e70>] pci_scan_single_device+0x90/0xe0 [<000001a19488a0f6>] zpci_bus_scan_device+0x46/0x80 [<000001a19547f958>] enable_slot+0x98/0xc0 [<000001a19547f134>] power_write_file+0xc4/0x110 [<000001a194e20758>] kernfs_fop_write_iter+0x1e8/0x260 [<000001a194d215da>] new_sync_write+0x13a/0x180 [<000001a194d245d0>] vfs_write+0x200/0x330 [<000001a194d2488c>] ksys_write+0x7c/0xf0 [<000001a195957a30>] __do_syscall+0x210/0x500 [<000001a19596cbb6>] system_call+0x6e/0x90 INFO: lockdep is turned off. Since it is desired to keep it possible to create trace records in most situations, including this particular case (failing PCI config space accesses are relevant), convert the used spinlock_t in `struct debug_info` to raw_spinlock_t. The impact is small, as the debug area lock only protects bounded memory access without external dependencies, apart from one function debug_set_size() where kfree() is implicitly called with the lock held. Move debug_info_free() out of this lock, to keep remove this external dependency. Acked-by: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: Benjamin Block <bblock@linux.ibm.com> Signed-off-by: Heiko Carstens <hca@linux.ibm.com> |
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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