docs: 新增 Linux 内核热补丁 sysfs 节点文档 (docs/livepatch-sysfs.md)

[Copilot]

新增面向内核/BPF 初学者的参考文档，系统讲解 /sys/kernel/livepatch sysfs 接口及 Linux livepatch 机制。

覆盖内容

• 原理：ftrace hook 函数替换机制、per-task 一致性模型与过渡状态机
• 节点结构：/sys/kernel/livepatch/<patch>/ 完整目录树，含 vmlinux 与内核模块补丁示例
• 关键文件：enabled、transition、force、patched、callbacks/ 的含义、取值、读写属性及注意事项
• 生命周期：加载 → 过渡 → 激活 → 禁用 → 卸载各阶段节点状态迁移速查表
• 框架对比：kpatch / 上游 livepatch / kGraft 的 sysfs 节点差异与一致性模型区别
• 操作速查：常用命令片段（insmod、kpatch、sysfs 写操作、rmmod 安全流程）
• 状态观测：判断补丁完整激活的三要素 + 综合状态 shell 脚本及示例输出
• 排错：transition 卡住（RT 任务/中断上下文）、rmmod -EBUSY、加载失败错误速查表、force 节点风险说明
• 参考资料：官方内核文档链接、kpatch 工具链、内核源码关键文件索引

Original prompt

新增文档《热补丁内核节点》到 docs/livepatch-sysfs.md，系统讲解 Linux 内核 livepatch（如 kpatch、livepatch、kgraft 框架）的 sysfs 节点 /sys/kernel/livepatch，包括：

• livepatch 子系统作用、用途，内核热补丁的主要原理简述；
• /sys/kernel/livepatch 节点下的目录、条目结构、每个关键文件（如 enable、transition、version、callbacks、loaded 等）的意义和常见取值说明；
• 手动/自动加载、启用、禁用热补丁时节点的变化流程；
• kpatch/livepatch/kgraft 之间与节点结构的细微区别；
• 常见操作命令、如何观测节点状态判断补丁激活与否；
• 排错思路，如“transition 卡住”等常见问题及 sysfs 层如何判断；
• 参考官方文档以及实际示例输出。

文档采用简体中文，内容为学习/排查热补丁 sysfs 节点入口资料，便于 BPF 或内核初学者理解原理和使用。该 PR 不涉及任何代码/功能变更，对现有内容无破坏性影响。

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: [ 0.929735] ------------[ cut here ]------------
[ 0.929736] WARNING: drivers/acpi/irq.c:63 at acpi_register_gsi+0xe0/0x100, CPU#0: swapper/0/1
[ 0.929740] Modules linked in:
[ 0.929742] CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Tainted: G W 7.1.0-rc1+ eunomia-bpf#4 PREEMPT(full)
[ 0.929745] Tainted: [W]=WARN
[ 0.929746] Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022
[ 0.929747] pc 9000000000df7ff0 ra 9000000000df7f7c tp 9000000100220000 sp 9000000100223a70
[ 0.929750] a0 0000000000000000 a1 0000000000000051 a2 0000000000000000 a3 0000000000000000
[ 0.929752] a4 9000000100223b10 a5 9000000100223b04 a6 9000000100223860 a7 0000000000000080
[ 0.929754] t0 0000000000000000 t1 90000000032f90c0 t2 ffffffffffffffff t3 0000000000000040
[ 0.929756] t4 0000000000000008 t5 90000000032fc3c8 t6 00000000000000f5 t7 0000800000000000
[ 0.929758] t8 000000000000002f u0 90000000018f8afc s9 90000000019740a8 s0 0000000000000051
[ 0.929760] s1 0000000000000000 s2 0000000000000000 s3 90000000025b5000 s4 0000000000000001
[ 0.929762] s5 900000010004b620 s6 9000000100b4d0c0 s7 9000000002473f18 s8 90000000019000b8
[ 0.929764] ra: 9000000000df7f7c acpi_register_gsi+0x6c/0x100
[ 0.929767] ERA: 9000000000df7ff0 acpi_register_gsi+0xe0/0x100
[ 0.929769] CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE)
[ 0.929775] PRMD: 00000004 (PPLV0 +PIE -PWE)
[ 0.929779] EUEN: 00000000 (-FPE -SXE -ASXE -BTE)
[ 0.929783] ECFG: 00071c3d (LIE=0,2-5,10-12 VS=7)
[ 0.929786] ESTAT: 000c0000 [BRK] (IS= ECode=12 EsubCode=0)
[ 0.929789] PRID: 0014c010 (Loongson-64bit, Loongson-3A5000)
[ 0.929792] CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Tainted: G W 7.1.0-rc1+ eunomia-bpf#4 PREEMPT(full)
[ 0.929795] Tainted: [W]=WARN
[ 0.929796] Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022
[ 0.929797] Stack : 9000000100223748 0000000000000000 90000000002478e4 9000000100220000
[ 0.929802] 9000000100223690 9000000100223698 0000000000000000 90000001002237d8
[ 0.929806] 90000001002237d0 90000001002237d0 9000000100223540 0000000000000001
[ 0.929810] 0000000000000001 9000000100223698 bb631f1dda87d000 90000000027b4b58
[ 0.929814] bfffffffffffed36 fffffffffffffffe 900000000331e710 ffffffffffff0a00
[ 0.929819] ffffffffffffb000 9000000001ffc662 000000026a628000 90000000019740a8
[ 0.929823] 0000000000000000 0000000000000000 9000000002279b68 90000000025b5000
[ 0.929827] 0000000000000009 000000000000003f 0000000000000002 9000000002473f18
[ 0.929832] 90000000019000b8 0000000000000000 90000000002478fc 00007fffefa5831c
[ 0.929836] 00000000000000b0 0000000000000004 0000000000000000 0000000000071c3d
[ 0.929840] ...
[ 0.929842] Call Trace:
[ 0.929843] [<90000000002478fc>] show_stack+0x5c/0x190
[ 0.929846] [<90000000002414fc>] dump_stack_lvl+0x9c/0xc8
[ 0.929851] [<900000000026d32c>] __warn+0x8c/0x140
[ 0.929856] [<90000000018b5878>] __report_bug+0x88/0x1c0
[ 0.929860] [<90000000018b5ab0>] report_bug+0x40/0xc0
[ 0.929864] [<90000000018ee7f4>] do_bp+0x314/0x3a0
[ 0.929866] [<9000000000245fe0>] handle_bp+0x120/0x1c0
[ 0.929869] [<9000000000df7ff0>] acpi_register_gsi+0xe0/0x100
[ 0.929872] [<9000000000defec8>] acpi_pci_irq_enable+0xd8/0x280
[ 0.929876] [<9000000000d71e14>] pci_device_probe+0x64/0x2d0
[ 0.929880] [<9000000000f8b0ec>] really_probe+0xbc/0x370
[ 0.929884] [<9000000000f8b42c>] __driver_probe_device+0x8c/0x1e0
[ 0.929888] [<9000000000f8b6a8>] driver_probe_device+0x38/0x150
[ 0.929891] [<9000000000f8b9e0>] __driver_attach+0xa0/0x1f0
[ 0.929895] [<9000000000f881d8>] bus_for_each_dev+0x88/0x110
[ 0.929898] [<9000000000f89dc4>] bus_add_driver+0x104/0x270
[ 0.929901] [<9000000000f8cb98>] driver_register+0x68/0x140
[ 0.929905] [<9000000000244168>] do_one_initcall+0x78/0x210
[ 0.929910] [<9000000001901290>] kernel_init_freeable+0x274/0x314
[ 0.929912] [<90000000018f12b0>] kernel_init+0x1c/0x12c
[ 0.929915] [<90000000018eea48>] ret_from_kernel_thread+0x28/0x1c0
[ 0.929918] [<90000000002456c4>] ret_from_kernel_thread_asm+0xc/0x88
[ 0.929921]
[ 0.929922] ---[ end trace 0000000000000000 ]---
[ 0.929924] GSI: No registered irqchip, giving up

Assistant: 这段 dmesg/堆栈里最关键的两条信息...

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