Re: [PATCH v4 00/35] Compiler-Based Context- and Locking-Analysis

[Marco Elver <elver@google.com>]

All,

On Thu, Nov 20, 2025 at 03:49PM +0100, Marco Elver wrote:
> Context Analysis is a language extension, which enables statically
> checking that required contexts are active (or inactive) by acquiring
> and releasing user-definable "context guards". An obvious application is
> lock-safety checking for the kernel's various synchronization primitives
> (each of which represents a "context guard"), and checking that locking
> rules are not violated.
[...] 
> A Clang version that supports `-Wthread-safety-pointer` and the new
> alias-analysis of context-guard pointers is required (from this version
> onwards):
> 
> 	https://github.com/llvm/llvm-project/commit/7ccb5c08f0685d4787f12c3224a72f0650c5865e
> 
> The minimum required release version will be Clang 22.
> 
> This series is also available at this Git tree:
> 
> 	https://git.kernel.org/pub/scm/linux/kernel/git/melver/linux.git/log/?h=ctx-analysis/dev
[...] 

I realize that I sent this series at the end of the last release cycle,
and now we're in the merge window, along with LPC going on -- so it
wasn't the best timing (however, it might be something to discuss at
LPC, too :-) .. I'm attending virtually, however :-/).

How to proceed?

I'll be preparing a rebased and retested version of all this when
v6.19-rc1 is out. One outstanding recommendation from Linus was to
investigate compile-times, but as-is, it's unclear there's any notable
overhead per brief investigation: https://lore.kernel.org/all/aR-plHrWDMqRRlcI@elver.google.com/

From what I can tell most of this has to go through the locking tree,
given the potential for conflict there. However, it is possible to split
this up as follows:

Batch 1:

>   compiler_types: Move lock checking attributes to
>     compiler-context-analysis.h
>   compiler-context-analysis: Add infrastructure for Context Analysis
>     with Clang
>   compiler-context-analysis: Add test stub
>   Documentation: Add documentation for Compiler-Based Context Analysis
>   checkpatch: Warn about context_unsafe() without comment
>   cleanup: Basic compatibility with context analysis
>   lockdep: Annotate lockdep assertions for context analysis
>   locking/rwlock, spinlock: Support Clang's context analysis
>   compiler-context-analysis: Change __cond_acquires to take return value
>   locking/mutex: Support Clang's context analysis
>   locking/seqlock: Support Clang's context analysis
>   bit_spinlock: Include missing <asm/processor.h>
>   bit_spinlock: Support Clang's context analysis
>   rcu: Support Clang's context analysis
>   srcu: Support Clang's context analysis
>   kref: Add context-analysis annotations
>   locking/rwsem: Support Clang's context analysis
>   locking/local_lock: Include missing headers
>   locking/local_lock: Support Clang's context analysis
>   locking/ww_mutex: Support Clang's context analysis
>   debugfs: Make debugfs_cancellation a context guard struct
>   compiler-context-analysis: Remove Sparse support
>   compiler-context-analysis: Remove __cond_lock() function-like helper
>   compiler-context-analysis: Introduce header suppressions
>   compiler: Let data_race() imply disabled context analysis
>   MAINTAINERS: Add entry for Context Analysis

Batch 2: Everything below this can wait for the initial support in
mainline, at which point subsystem maintainers can pick them up if
deemed appropriate.

>   kfence: Enable context analysis
>   kcov: Enable context analysis
>   kcsan: Enable context analysis
>   stackdepot: Enable context analysis
>   rhashtable: Enable context analysis
>   printk: Move locking annotation to printk.c
>   security/tomoyo: Enable context analysis
>   crypto: Enable context analysis
>   sched: Enable context analysis for core.c and fair.c

Thanks,
	-- Marco