[PATCH v4 20/35] locking/ww_mutex: Support Clang's context analysis

[Marco Elver <elver@google.com>]

Add support for Clang's context analysis for ww_mutex.

The programming model for ww_mutex is subtly more complex than other
locking primitives when using ww_acquire_ctx. Encoding the respective
pre-conditions for ww_mutex lock/unlock based on ww_acquire_ctx state
using Clang's context analysis makes incorrect use of the API harder.

Signed-off-by: Marco Elver <elver@google.com>
---
v4:
* Rename capability -> context analysis.

v3:
* __assert -> __assume rename

v2:
* New patch.
---
 Documentation/dev-tools/context-analysis.rst |  3 +-
 include/linux/ww_mutex.h                     | 22 +++++--
 lib/test_context-analysis.c                  | 69 ++++++++++++++++++++
 3 files changed, 87 insertions(+), 7 deletions(-)

diff --git a/Documentation/dev-tools/context-analysis.rst b/Documentation/dev-tools/context-analysis.rst
index 8737de63a707..2936666651f3 100644
--- a/Documentation/dev-tools/context-analysis.rst
+++ b/Documentation/dev-tools/context-analysis.rst
@@ -81,7 +81,8 @@ 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`.
+`bit_spinlock`, RCU, SRCU (`srcu_struct`), `rw_semaphore`, `local_lock_t`,
+`ww_mutex`.
 
 For context guards with an initialization function (e.g., `spin_lock_init()`),
 calling this function before initializing any guarded members or globals
diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
index 45ff6f7a872b..f6253e8ba9af 100644
--- a/include/linux/ww_mutex.h
+++ b/include/linux/ww_mutex.h
@@ -44,7 +44,7 @@ struct ww_class {
 	unsigned int is_wait_die;
 };
 
-struct ww_mutex {
+context_guard_struct(ww_mutex) {
 	struct WW_MUTEX_BASE base;
 	struct ww_acquire_ctx *ctx;
 #ifdef DEBUG_WW_MUTEXES
@@ -52,7 +52,7 @@ struct ww_mutex {
 #endif
 };
 
-struct ww_acquire_ctx {
+context_guard_struct(ww_acquire_ctx) {
 	struct task_struct *task;
 	unsigned long stamp;
 	unsigned int acquired;
@@ -107,6 +107,7 @@ struct ww_acquire_ctx {
  */
 static inline void ww_mutex_init(struct ww_mutex *lock,
 				 struct ww_class *ww_class)
+	__assumes_ctx_guard(lock)
 {
 	ww_mutex_base_init(&lock->base, ww_class->mutex_name, &ww_class->mutex_key);
 	lock->ctx = NULL;
@@ -141,6 +142,7 @@ static inline void ww_mutex_init(struct ww_mutex *lock,
  */
 static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
 				   struct ww_class *ww_class)
+	__acquires(ctx) __no_context_analysis
 {
 	ctx->task = current;
 	ctx->stamp = atomic_long_inc_return_relaxed(&ww_class->stamp);
@@ -179,6 +181,7 @@ static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
  * data structures.
  */
 static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
+	__releases(ctx) __acquires_shared(ctx) __no_context_analysis
 {
 #ifdef DEBUG_WW_MUTEXES
 	lockdep_assert_held(ctx);
@@ -196,6 +199,7 @@ static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
  * mutexes have been released with ww_mutex_unlock.
  */
 static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
+	__releases_shared(ctx) __no_context_analysis
 {
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	mutex_release(&ctx->first_lock_dep_map, _THIS_IP_);
@@ -245,7 +249,8 @@ static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
  *
  * A mutex acquired with this function must be released with ww_mutex_unlock.
  */
-extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx);
+extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+	__cond_acquires(0, lock) __must_hold(ctx);
 
 /**
  * ww_mutex_lock_interruptible - acquire the w/w mutex, interruptible
@@ -278,7 +283,8 @@ extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acq
  * A mutex acquired with this function must be released with ww_mutex_unlock.
  */
 extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
-						    struct ww_acquire_ctx *ctx);
+						    struct ww_acquire_ctx *ctx)
+	__cond_acquires(0, lock) __must_hold(ctx);
 
 /**
  * ww_mutex_lock_slow - slowpath acquiring of the w/w mutex
@@ -305,6 +311,7 @@ extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
  */
 static inline void
 ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+	__acquires(lock) __must_hold(ctx) __no_context_analysis
 {
 	int ret;
 #ifdef DEBUG_WW_MUTEXES
@@ -342,6 +349,7 @@ ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 static inline int __must_check
 ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,
 				 struct ww_acquire_ctx *ctx)
+	__cond_acquires(0, lock) __must_hold(ctx)
 {
 #ifdef DEBUG_WW_MUTEXES
 	DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
@@ -349,10 +357,11 @@ ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,
 	return ww_mutex_lock_interruptible(lock, ctx);
 }
 
-extern void ww_mutex_unlock(struct ww_mutex *lock);
+extern void ww_mutex_unlock(struct ww_mutex *lock) __releases(lock);
 
 extern int __must_check ww_mutex_trylock(struct ww_mutex *lock,
-					 struct ww_acquire_ctx *ctx);
+					 struct ww_acquire_ctx *ctx)
+	__cond_acquires(true, lock) __must_hold(ctx);
 
 /***
  * ww_mutex_destroy - mark a w/w mutex unusable
@@ -363,6 +372,7 @@ extern int __must_check ww_mutex_trylock(struct ww_mutex *lock,
  * this function is called.
  */
 static inline void ww_mutex_destroy(struct ww_mutex *lock)
+	__must_not_hold(lock)
 {
 #ifndef CONFIG_PREEMPT_RT
 	mutex_destroy(&lock->base);
diff --git a/lib/test_context-analysis.c b/lib/test_context-analysis.c
index 74eca21f7aaa..522769c9586d 100644
--- a/lib/test_context-analysis.c
+++ b/lib/test_context-analysis.c
@@ -14,6 +14,7 @@
 #include <linux/seqlock.h>
 #include <linux/spinlock.h>
 #include <linux/srcu.h>
+#include <linux/ww_mutex.h>
 
 /*
  * Test that helper macros work as expected.
@@ -523,3 +524,71 @@ static void __used test_local_trylock(void)
 		local_unlock(&test_local_trylock_data.lock);
 	}
 }
+
+static DEFINE_WD_CLASS(ww_class);
+
+struct test_ww_mutex_data {
+	struct ww_mutex mtx;
+	int counter __guarded_by(&mtx);
+};
+
+static void __used test_ww_mutex_init(struct test_ww_mutex_data *d)
+{
+	ww_mutex_init(&d->mtx, &ww_class);
+	d->counter = 0;
+}
+
+static void __used test_ww_mutex_lock_noctx(struct test_ww_mutex_data *d)
+{
+	if (!ww_mutex_lock(&d->mtx, NULL)) {
+		d->counter++;
+		ww_mutex_unlock(&d->mtx);
+	}
+
+	if (!ww_mutex_lock_interruptible(&d->mtx, NULL)) {
+		d->counter++;
+		ww_mutex_unlock(&d->mtx);
+	}
+
+	if (ww_mutex_trylock(&d->mtx, NULL)) {
+		d->counter++;
+		ww_mutex_unlock(&d->mtx);
+	}
+
+	ww_mutex_lock_slow(&d->mtx, NULL);
+	d->counter++;
+	ww_mutex_unlock(&d->mtx);
+
+	ww_mutex_destroy(&d->mtx);
+}
+
+static void __used test_ww_mutex_lock_ctx(struct test_ww_mutex_data *d)
+{
+	struct ww_acquire_ctx ctx;
+
+	ww_acquire_init(&ctx, &ww_class);
+
+	if (!ww_mutex_lock(&d->mtx, &ctx)) {
+		d->counter++;
+		ww_mutex_unlock(&d->mtx);
+	}
+
+	if (!ww_mutex_lock_interruptible(&d->mtx, &ctx)) {
+		d->counter++;
+		ww_mutex_unlock(&d->mtx);
+	}
+
+	if (ww_mutex_trylock(&d->mtx, &ctx)) {
+		d->counter++;
+		ww_mutex_unlock(&d->mtx);
+	}
+
+	ww_mutex_lock_slow(&d->mtx, &ctx);
+	d->counter++;
+	ww_mutex_unlock(&d->mtx);
+
+	ww_acquire_done(&ctx);
+	ww_acquire_fini(&ctx);
+
+	ww_mutex_destroy(&d->mtx);
+}
-- 
2.52.0.rc1.455.g30608eb744-goog