---
name: kernel-b8678917bd9e
description: Avoid common Linux kernel mistakes — atomic context violations, allocation failures, and locking traps.
metadata: {"clawdbot":{"emoji":"🐧","os":["linux"]}}
---

## Atomic Context Traps
- `spin_lock` held = cannot sleep — no `kmalloc(GFP_KERNEL)`, no `mutex_lock`, no `copy_from_user`
- Interrupt can take same spinlock — must use `spin_lock_irqsave`, not plain `spin_lock`
- `rcu_read_lock()` section cannot sleep — no blocking calls inside RCU read-side
- `might_sleep()` annotation — add to functions that may sleep, catches bugs with `CONFIG_DEBUG_ATOMIC_SLEEP`

## Allocation Failures
- `GFP_ATOMIC` can return NULL — always check, don't assume success
- `vmalloc` memory not physically contiguous — cannot use for DMA
- `kzalloc` over `kmalloc` — uninitialized memory leaks kernel info to userspace
- Allocation in loop risks OOM — preallocate or use memory pool

## User Pointer Handling
- `copy_from_user` returns bytes NOT copied — 0 means success, not failure
- Never use `%s` with user pointer in printk — kernel crash or info leak
- User memory can change during syscall — copy to kernel buffer, validate the copy
- `__user` annotation is documentation — doesn't enforce anything, you must use copy functions

## Memory Ordering
- `READ_ONCE`/`WRITE_ONCE` for lockless shared data — prevents compiler from caching/reordering
- Spinlock release has implicit barrier — but check-then-act patterns still need care
- `smp_wmb()` before publishing pointer — ensures data visible before pointer is

## Module Error Paths
- Init fails midway — must undo everything already done
- Reverse order cleanup — unregister in opposite order of register
- `goto err_*` pattern standard — cleaner than nested ifs
- Check what's actually initialized — don't free/unregister what wasn't set up

## Locking Mistakes
- Same lock acquired twice = deadlock — even in different functions
- Inconsistent lock ordering — document order, acquire in same sequence everywhere
- `mutex_trylock` returns 1 on success — opposite of `pthread_mutex_trylock`
- Reader-writer locks rarely worth it — contention overhead usually exceeds benefit


---
Source attribution: modbender
Original project: https://github.com/modbender/skill-library-mcp/blob/d9c8fe903b5b4e82237dbe8d0df8567783022e18/data/kernel/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2025 skill-library-mcp contributors

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: modbender
Original project: https://github.com/modbender/skill-library-mcp/blob/d9c8fe903b5b4e82237dbe8d0df8567783022e18/data/kernel/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering
Roles: Backend Developer, DevOps / SRE, ML / AI Engineer
Specialties: Backend
Tools: Linux
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: 30fb4df7c61bfb19e1fbcc3424cee15b4dc4f0ab46b42b547d581b51a7512c1c