Merge tag 'locking-core-2026-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking updates from Ingo Molnar:
 "Lock debugging:

   - Implement compiler-driven static analysis locking context checking,
     using the upcoming Clang 22 compiler's context analysis features
     (Marco Elver)

     We removed Sparse context analysis support, because prior to
     removal even a defconfig kernel produced 1,700+ context tracking
     Sparse warnings, the overwhelming majority of which are false
     positives. On an allmodconfig kernel the number of false positive
     context tracking Sparse warnings grows to over 5,200... On the plus
     side of the balance actual locking bugs found by Sparse context
     analysis is also rather ... sparse: I found only 3 such commits in
     the last 3 years. So the rate of false positives and the
     maintenance overhead is rather high and there appears to be no
     active policy in place to achieve a zero-warnings baseline to move
     the annotations & fixers to developers who introduce new code.

     Clang context analysis is more complete and more aggressive in
     trying to find bugs, at least in principle. Plus it has a different
     model to enabling it: it's enabled subsystem by subsystem, which
     results in zero warnings on all relevant kernel builds (as far as
     our testing managed to cover it). Which allowed us to enable it by
     default, similar to other compiler warnings, with the expectation
     that there are no warnings going forward. This enforces a
     zero-warnings baseline on clang-22+ builds (Which are still limited
     in distribution, admittedly)

     Hopefully the Clang approach can lead to a more maintainable
     zero-warnings status quo and policy, with more and more subsystems
     and drivers enabling the feature. Context tracking can be enabled
     for all kernel code via WARN_CONTEXT_ANALYSIS_ALL=y (default
     disabled), but this will generate a lot of false positives.

     ( Having said that, Sparse support could still be added back,
       if anyone is interested - the removal patch is still
       relatively straightforward to revert at this stage. )

  Rust integration updates: (Alice Ryhl, Fujita Tomonori, Boqun Feng)

    - Add support for Atomic<i8/i16/bool> and replace most Rust native
      AtomicBool usages with Atomic<bool>

    - Clean up LockClassKey and improve its documentation

    - Add missing Send and Sync trait implementation for SetOnce

    - Make ARef Unpin as it is supposed to be

    - Add __rust_helper to a few Rust helpers as a preparation for
      helper LTO

    - Inline various lock related functions to avoid additional function
      calls

  WW mutexes:

    - Extend ww_mutex tests and other test-ww_mutex updates (John
      Stultz)

  Misc fixes and cleanups:

    - rcu: Mark lockdep_assert_rcu_helper() __always_inline (Arnd
      Bergmann)

    - locking/local_lock: Include more missing headers (Peter Zijlstra)

    - seqlock: fix scoped_seqlock_read kernel-doc (Randy Dunlap)

    - rust: sync: Replace `kernel::c_str!` with C-Strings (Tamir
      Duberstein)"

* tag 'locking-core-2026-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (90 commits)
  locking/rwlock: Fix write_trylock_irqsave() with CONFIG_INLINE_WRITE_TRYLOCK
  rcu: Mark lockdep_assert_rcu_helper() __always_inline
  compiler-context-analysis: Remove __assume_ctx_lock from initializers
  tomoyo: Use scoped init guard
  crypto: Use scoped init guard
  kcov: Use scoped init guard
  compiler-context-analysis: Introduce scoped init guards
  cleanup: Make __DEFINE_LOCK_GUARD handle commas in initializers
  seqlock: fix scoped_seqlock_read kernel-doc
  tools: Update context analysis macros in compiler_types.h
  rust: sync: Replace `kernel::c_str!` with C-Strings
  rust: sync: Inline various lock related methods
  rust: helpers: Move #define __rust_helper out of atomic.c
  rust: wait: Add __rust_helper to helpers
  rust: time: Add __rust_helper to helpers
  rust: task: Add __rust_helper to helpers
  rust: sync: Add __rust_helper to helpers
  rust: refcount: Add __rust_helper to helpers
  rust: rcu: Add __rust_helper to helpers
  rust: processor: Add __rust_helper to helpers
  ...

3 files changed, 170 insertions, 19 deletions

diff --git a/Documentation/dev-tools/context-analysis.rst b/Documentation/dev-tools/context-analysis.rst
new file mode 100644
index 000000000000..54d9ee28de98
--- /dev/null
+++ b/Documentation/dev-tools/context-analysis.rst
@@ -0,0 +1,169 @@
+.. SPDX-License-Identifier: GPL-2.0
+.. Copyright (C) 2025, Google LLC.
+
+.. _context-analysis:
+
+Compiler-Based Context Analysis
+===============================
+
+Context Analysis is a language extension, which enables statically checking
+that required contexts are active (or inactive) by acquiring and releasing
+user-definable "context locks". An obvious application is lock-safety checking
+for the kernel's various synchronization primitives (each of which represents a
+"context lock"), and checking that locking rules are not violated.
+
+The Clang compiler currently supports the full set of context analysis
+features. To enable for Clang, configure the kernel with::
+
+    CONFIG_WARN_CONTEXT_ANALYSIS=y
+
+The feature requires Clang 22 or later.
+
+The analysis is *opt-in by default*, and requires declaring which modules and
+subsystems should be analyzed in the respective `Makefile`::
+
+    CONTEXT_ANALYSIS_mymodule.o := y
+
+Or for all translation units in the directory::
+
+    CONTEXT_ANALYSIS := y
+
+It is possible to enable the analysis tree-wide, however, which will result in
+numerous false positive warnings currently and is *not* generally recommended::
+
+    CONFIG_WARN_CONTEXT_ANALYSIS_ALL=y
+
+Programming Model
+-----------------
+
+The below describes the programming model around using context lock types.
+
+.. note::
+   Enabling context analysis can be seen as enabling a dialect of Linux C with
+   a Context System. Some valid patterns involving complex control-flow are
+   constrained (such as conditional acquisition and later conditional release
+   in the same function).
+
+Context analysis is a way to specify permissibility of operations to depend on
+context locks being held (or not held). Typically we are interested in
+protecting data and code in a critical section by requiring a specific context
+to be active, for example by holding a specific lock. The analysis ensures that
+callers cannot perform an operation without the required context being active.
+
+Context locks are associated with named structs, along with functions that
+operate on struct instances to acquire and release the associated context lock.
+
+Context locks can be held either exclusively or shared. This mechanism allows
+assigning more precise privileges when a context is active, typically to
+distinguish where a thread may only read (shared) or also write (exclusive) to
+data guarded within a context.
+
+The set of contexts that are actually active in a given thread at a given point
+in program execution is a run-time concept. The static analysis works by
+calculating an approximation of that set, called the context environment. The
+context environment is calculated for every program point, and describes the
+set of contexts that are statically known to be active, or inactive, at that
+particular point. This environment is a conservative approximation of the full
+set of contexts that will actually be active in a thread at run-time.
+
+More details are also documented `here
+<https://clang.llvm.org/docs/ThreadSafetyAnalysis.html>`_.
+
+.. note::
+   Clang's analysis explicitly does not infer context locks acquired or
+   released by inline functions. It requires explicit annotations to (a) assert
+   that it's not a bug if a context lock is released or acquired, and (b) to
+   retain consistency between inline and non-inline function declarations.
+
+Supported Kernel Primitives
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Currently the following synchronization primitives are supported:
+`raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`, `seqlock_t`,
+`bit_spinlock`, RCU, SRCU (`srcu_struct`), `rw_semaphore`, `local_lock_t`,
+`ww_mutex`.
+
+To initialize variables guarded by a context lock with an initialization
+function (``type_init(&lock)``), prefer using ``guard(type_init)(&lock)`` or
+``scoped_guard(type_init, &lock) { ... }`` to initialize such guarded members
+or globals in the enclosing scope. This initializes the context lock and treats
+the context as active within the initialization scope (initialization implies
+exclusive access to the underlying object).
+
+For example::
+
+    struct my_data {
+            spinlock_t lock;
+            int counter __guarded_by(&lock);
+    };
+
+    void init_my_data(struct my_data *d)
+    {
+            ...
+            guard(spinlock_init)(&d->lock);
+            d->counter = 0;
+            ...
+    }
+
+Alternatively, initializing guarded variables can be done with context analysis
+disabled, preferably in the smallest possible scope (due to lack of any other
+checking): either with a ``context_unsafe(var = init)`` expression, or by
+marking small initialization functions with the ``__context_unsafe(init)``
+attribute.
+
+Lockdep assertions, such as `lockdep_assert_held()`, inform the compiler's
+context analysis that the associated synchronization primitive is held after
+the assertion. This avoids false positives in complex control-flow scenarios
+and encourages the use of Lockdep where static analysis is limited. For
+example, this is useful when a function doesn't *always* require a lock, making
+`__must_hold()` inappropriate.
+
+Keywords
+~~~~~~~~
+
+.. kernel-doc:: include/linux/compiler-context-analysis.h
+   :identifiers: context_lock_struct
+                 token_context_lock token_context_lock_instance
+                 __guarded_by __pt_guarded_by
+                 __must_hold
+                 __must_not_hold
+                 __acquires
+                 __cond_acquires
+                 __releases
+                 __must_hold_shared
+                 __acquires_shared
+                 __cond_acquires_shared
+                 __releases_shared
+                 __acquire
+                 __release
+                 __acquire_shared
+                 __release_shared
+                 __acquire_ret
+                 __acquire_shared_ret
+                 context_unsafe
+                 __context_unsafe
+                 disable_context_analysis enable_context_analysis
+
+.. note::
+   The function attribute `__no_context_analysis` is reserved for internal
+   implementation of context lock types, and should be avoided in normal code.
+
+Background
+----------
+
+Clang originally called the feature `Thread Safety Analysis
+<https://clang.llvm.org/docs/ThreadSafetyAnalysis.html>`_, with some keywords
+and documentation still using the thread-safety-analysis-only terminology. This
+was later changed and the feature became more flexible, gaining the ability to
+define custom "capabilities". Its foundations can be found in `Capability
+Systems <https://www.cs.cornell.edu/talc/papers/capabilities.pdf>`_, used to
+specify the permissibility of operations to depend on some "capability" being
+held (or not held).
+
+Because the feature is not just able to express capabilities related to
+synchronization primitives, and "capability" is already overloaded in the
+kernel, the naming chosen for the kernel departs from Clang's initial "Thread
+Safety" and "capability" nomenclature; we refer to the feature as "Context
+Analysis" to avoid confusion. The internal implementation still makes
+references to Clang's terminology in a few places, such as `-Wthread-safety`
+being the warning option that also still appears in diagnostic messages.
diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
index 4fc9d15f91d0..1477c10e1356 100644
--- a/Documentation/dev-tools/index.rst
+++ b/Documentation/dev-tools/index.rst
@@ -21,6 +21,7 @@ Documentation/process/debugging/index.rst
    checkpatch
    clang-format
    coccinelle
+   context-analysis
    sparse
    kcov
    gcov
diff --git a/Documentation/dev-tools/sparse.rst b/Documentation/dev-tools/sparse.rst
index dc791c8d84d1..37b20170835d 100644
--- a/Documentation/dev-tools/sparse.rst
+++ b/Documentation/dev-tools/sparse.rst
@@ -53,25 +53,6 @@ sure that bitwise types don't get mixed up (little-endian vs big-endian
 vs cpu-endian vs whatever), and there the constant "0" really _is_
 special.
 
-Using sparse for lock checking
-------------------------------
-
-The following macros are undefined for gcc and defined during a sparse
-run to use the "context" tracking feature of sparse, applied to
-locking.  These annotations tell sparse when a lock is held, with
-regard to the annotated function's entry and exit.
-
-__must_hold - The specified lock is held on function entry and exit.
-
-__acquires - The specified lock is held on function exit, but not entry.
-
-__releases - The specified lock is held on function entry, but not exit.
-
-If the function enters and exits without the lock held, acquiring and
-releasing the lock inside the function in a balanced way, no
-annotation is needed.  The three annotations above are for cases where
-sparse would otherwise report a context imbalance.
-
 Getting sparse
 --------------