mutex: Add support for wound/wait style locks

Wound/wait mutexes are used when other multiple lock
acquisitions of a similar type can be done in an arbitrary
order. The deadlock handling used here is called wait/wound in
the RDBMS literature: The older tasks waits until it can acquire
the contended lock. The younger tasks needs to back off and drop
all the locks it is currently holding, i.e. the younger task is
wounded.

For full documentation please read Documentation/ww-mutex-design.txt.

References: https://lwn.net/Articles/548909/
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Rob Clark <robdclark@gmail.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org
Cc: rostedt@goodmis.org
Cc: daniel@ffwll.ch
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/51C8038C.9000106@canonical.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 355 insertions, 1 deletions

diff --git a/include/linux/mutex-debug.h b/include/linux/mutex-debug.h
index 731d77d6e15..4ac8b1977b7 100644
--- a/include/linux/mutex-debug.h
+++ b/include/linux/mutex-debug.h
@@ -3,6 +3,7 @@
 
 #include <linux/linkage.h>
 #include <linux/lockdep.h>
+#include <linux/debug_locks.h>
 
 /*
  * Mutexes - debugging helpers:
diff --git a/include/linux/mutex.h b/include/linux/mutex.h
index 433da8a1a42..a56b0ccc8a6 100644
--- a/include/linux/mutex.h
+++ b/include/linux/mutex.h
@@ -10,6 +10,7 @@
 #ifndef __LINUX_MUTEX_H
 #define __LINUX_MUTEX_H
 
+#include <asm/current.h>
 #include <linux/list.h>
 #include <linux/spinlock_types.h>
 #include <linux/linkage.h>
@@ -77,6 +78,36 @@ struct mutex_waiter {
 #endif
 };
 
+struct ww_class {
+	atomic_long_t stamp;
+	struct lock_class_key acquire_key;
+	struct lock_class_key mutex_key;
+	const char *acquire_name;
+	const char *mutex_name;
+};
+
+struct ww_acquire_ctx {
+	struct task_struct *task;
+	unsigned long stamp;
+	unsigned acquired;
+#ifdef CONFIG_DEBUG_MUTEXES
+	unsigned done_acquire;
+	struct ww_class *ww_class;
+	struct ww_mutex *contending_lock;
+#endif
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map dep_map;
+#endif
+};
+
+struct ww_mutex {
+	struct mutex base;
+	struct ww_acquire_ctx *ctx;
+#ifdef CONFIG_DEBUG_MUTEXES
+	struct ww_class *ww_class;
+#endif
+};
+
 #ifdef CONFIG_DEBUG_MUTEXES
 # include <linux/mutex-debug.h>
 #else
@@ -101,8 +132,11 @@ static inline void mutex_destroy(struct mutex *lock) {}
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
 		, .dep_map = { .name = #lockname }
+# define __WW_CLASS_MUTEX_INITIALIZER(lockname, ww_class) \
+		, .ww_class = &ww_class
 #else
 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
+# define __WW_CLASS_MUTEX_INITIALIZER(lockname, ww_class)
 #endif
 
 #define __MUTEX_INITIALIZER(lockname) \
@@ -112,13 +146,49 @@ static inline void mutex_destroy(struct mutex *lock) {}
 		__DEBUG_MUTEX_INITIALIZER(lockname) \
 		__DEP_MAP_MUTEX_INITIALIZER(lockname) }
 
+#define __WW_CLASS_INITIALIZER(ww_class) \
+		{ .stamp = ATOMIC_LONG_INIT(0) \
+		, .acquire_name = #ww_class "_acquire" \
+		, .mutex_name = #ww_class "_mutex" }
+
+#define __WW_MUTEX_INITIALIZER(lockname, class) \
+		{ .base = { \__MUTEX_INITIALIZER(lockname) } \
+		__WW_CLASS_MUTEX_INITIALIZER(lockname, class) }
+
 #define DEFINE_MUTEX(mutexname) \
 	struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
 
+#define DEFINE_WW_CLASS(classname) \
+	struct ww_class classname = __WW_CLASS_INITIALIZER(classname)
+
+#define DEFINE_WW_MUTEX(mutexname, ww_class) \
+	struct ww_mutex mutexname = __WW_MUTEX_INITIALIZER(mutexname, ww_class)
+
+
 extern void __mutex_init(struct mutex *lock, const char *name,
 			 struct lock_class_key *key);
 
 /**
+ * ww_mutex_init - initialize the w/w mutex
+ * @lock: the mutex to be initialized
+ * @ww_class: the w/w class the mutex should belong to
+ *
+ * Initialize the w/w mutex to unlocked state and associate it with the given
+ * class.
+ *
+ * It is not allowed to initialize an already locked mutex.
+ */
+static inline void ww_mutex_init(struct ww_mutex *lock,
+				 struct ww_class *ww_class)
+{
+	__mutex_init(&lock->base, ww_class->mutex_name, &ww_class->mutex_key);
+	lock->ctx = NULL;
+#ifdef CONFIG_DEBUG_MUTEXES
+	lock->ww_class = ww_class;
+#endif
+}
+
+/**
  * mutex_is_locked - is the mutex locked
  * @lock: the mutex to be queried
  *
@@ -136,6 +206,7 @@ static inline int mutex_is_locked(struct mutex *lock)
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
 extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
+
 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
 					unsigned int subclass);
 extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
@@ -147,7 +218,7 @@ extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
 
 #define mutex_lock_nest_lock(lock, nest_lock)				\
 do {									\
-	typecheck(struct lockdep_map *, &(nest_lock)->dep_map);		\
+	typecheck(struct lockdep_map *, &(nest_lock)->dep_map);	\
 	_mutex_lock_nest_lock(lock, &(nest_lock)->dep_map);		\
 } while (0)
 
@@ -170,6 +241,288 @@ extern int __must_check mutex_lock_killable(struct mutex *lock);
  */
 extern int mutex_trylock(struct mutex *lock);
 extern void mutex_unlock(struct mutex *lock);
+
+/**
+ * ww_acquire_init - initialize a w/w acquire context
+ * @ctx: w/w acquire context to initialize
+ * @ww_class: w/w class of the context
+ *
+ * Initializes an context to acquire multiple mutexes of the given w/w class.
+ *
+ * Context-based w/w mutex acquiring can be done in any order whatsoever within
+ * a given lock class. Deadlocks will be detected and handled with the
+ * wait/wound logic.
+ *
+ * Mixing of context-based w/w mutex acquiring and single w/w mutex locking can
+ * result in undetected deadlocks and is so forbidden. Mixing different contexts
+ * for the same w/w class when acquiring mutexes can also result in undetected
+ * deadlocks, and is hence also forbidden. Both types of abuse will be caught by
+ * enabling CONFIG_PROVE_LOCKING.
+ *
+ * Nesting of acquire contexts for _different_ w/w classes is possible, subject
+ * to the usual locking rules between different lock classes.
+ *
+ * An acquire context must be released with ww_acquire_fini by the same task
+ * before the memory is freed. It is recommended to allocate the context itself
+ * on the stack.
+ */
+static inline void ww_acquire_init(struct ww_acquire_ctx *ctx,
+				   struct ww_class *ww_class)
+{
+	ctx->task = current;
+	ctx->stamp = atomic_long_inc_return(&ww_class->stamp);
+	ctx->acquired = 0;
+#ifdef CONFIG_DEBUG_MUTEXES
+	ctx->ww_class = ww_class;
+	ctx->done_acquire = 0;
+	ctx->contending_lock = NULL;
+#endif
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	debug_check_no_locks_freed((void *)ctx, sizeof(*ctx));
+	lockdep_init_map(&ctx->dep_map, ww_class->acquire_name,
+			 &ww_class->acquire_key, 0);
+	mutex_acquire(&ctx->dep_map, 0, 0, _RET_IP_);
+#endif
+}
+
+/**
+ * ww_acquire_done - marks the end of the acquire phase
+ * @ctx: the acquire context
+ *
+ * Marks the end of the acquire phase, any further w/w mutex lock calls using
+ * this context are forbidden.
+ *
+ * Calling this function is optional, it is just useful to document w/w mutex
+ * code and clearly designated the acquire phase from actually using the locked
+ * data structures.
+ */
+static inline void ww_acquire_done(struct ww_acquire_ctx *ctx)
+{
+#ifdef CONFIG_DEBUG_MUTEXES
+	lockdep_assert_held(ctx);
+
+	DEBUG_LOCKS_WARN_ON(ctx->done_acquire);
+	ctx->done_acquire = 1;
+#endif
+}
+
+/**
+ * ww_acquire_fini - releases a w/w acquire context
+ * @ctx: the acquire context to free
+ *
+ * Releases a w/w acquire context. This must be called _after_ all acquired w/w
+ * mutexes have been released with ww_mutex_unlock.
+ */
+static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
+{
+#ifdef CONFIG_DEBUG_MUTEXES
+	mutex_release(&ctx->dep_map, 0, _THIS_IP_);
+
+	DEBUG_LOCKS_WARN_ON(ctx->acquired);
+	if (!config_enabled(CONFIG_PROVE_LOCKING))
+		/*
+		 * lockdep will normally handle this,
+		 * but fail without anyway
+		 */
+		ctx->done_acquire = 1;
+
+	if (!config_enabled(CONFIG_DEBUG_LOCK_ALLOC))
+		/* ensure ww_acquire_fini will still fail if called twice */
+		ctx->acquired = ~0U;
+#endif
+}
+
+extern int __must_check __ww_mutex_lock(struct ww_mutex *lock,
+					struct ww_acquire_ctx *ctx);
+extern int __must_check __ww_mutex_lock_interruptible(struct ww_mutex *lock,
+						      struct ww_acquire_ctx *ctx);
+
+/**
+ * ww_mutex_lock - acquire the w/w mutex
+ * @lock: the mutex to be acquired
+ * @ctx: w/w acquire context, or NULL to acquire only a single lock.
+ *
+ * Lock the w/w mutex exclusively for this task.
+ *
+ * Deadlocks within a given w/w class of locks are detected and handled with the
+ * wait/wound algorithm. If the lock isn't immediately avaiable this function
+ * will either sleep until it is (wait case). Or it selects the current context
+ * for backing off by returning -EDEADLK (wound case). Trying to acquire the
+ * same lock with the same context twice is also detected and signalled by
+ * returning -EALREADY. Returns 0 if the mutex was successfully acquired.
+ *
+ * In the wound case the caller must release all currently held w/w mutexes for
+ * the given context and then wait for this contending lock to be available by
+ * calling ww_mutex_lock_slow. Alternatively callers can opt to not acquire this
+ * lock and proceed with trying to acquire further w/w mutexes (e.g. when
+ * scanning through lru lists trying to free resources).
+ *
+ * The mutex must later on be released by the same task that
+ * acquired it. The task may not exit without first unlocking the mutex. Also,
+ * kernel memory where the mutex resides must not be freed with the mutex still
+ * locked. The mutex must first be initialized (or statically defined) before it
+ * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
+ * of the same w/w lock class as was used to initialize the acquire context.
+ *
+ * A mutex acquired with this function must be released with ww_mutex_unlock.
+ */
+static inline int ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+{
+	if (ctx)
+		return __ww_mutex_lock(lock, ctx);
+	else {
+		mutex_lock(&lock->base);
+		return 0;
+	}
+}
+
+/**
+ * ww_mutex_lock_interruptible - acquire the w/w mutex, interruptible
+ * @lock: the mutex to be acquired
+ * @ctx: w/w acquire context
+ *
+ * Lock the w/w mutex exclusively for this task.
+ *
+ * Deadlocks within a given w/w class of locks are detected and handled with the
+ * wait/wound algorithm. If the lock isn't immediately avaiable this function
+ * will either sleep until it is (wait case). Or it selects the current context
+ * for backing off by returning -EDEADLK (wound case). Trying to acquire the
+ * same lock with the same context twice is also detected and signalled by
+ * returning -EALREADY. Returns 0 if the mutex was successfully acquired. If a
+ * signal arrives while waiting for the lock then this function returns -EINTR.
+ *
+ * In the wound case the caller must release all currently held w/w mutexes for
+ * the given context and then wait for this contending lock to be available by
+ * calling ww_mutex_lock_slow_interruptible. Alternatively callers can opt to
+ * not acquire this lock and proceed with trying to acquire further w/w mutexes
+ * (e.g. when scanning through lru lists trying to free resources).
+ *
+ * The mutex must later on be released by the same task that
+ * acquired it. The task may not exit without first unlocking the mutex. Also,
+ * kernel memory where the mutex resides must not be freed with the mutex still
+ * locked. The mutex must first be initialized (or statically defined) before it
+ * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
+ * of the same w/w lock class as was used to initialize the acquire context.
+ *
+ * A mutex acquired with this function must be released with ww_mutex_unlock.
+ */
+static inline int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
+							   struct ww_acquire_ctx *ctx)
+{
+	if (ctx)
+		return __ww_mutex_lock_interruptible(lock, ctx);
+	else
+		return mutex_lock_interruptible(&lock->base);
+}
+
+/**
+ * ww_mutex_lock_slow - slowpath acquiring of the w/w mutex
+ * @lock: the mutex to be acquired
+ * @ctx: w/w acquire context
+ *
+ * Acquires a w/w mutex with the given context after a wound case. This function
+ * will sleep until the lock becomes available.
+ *
+ * The caller must have released all w/w mutexes already acquired with the
+ * context and then call this function on the contended lock.
+ *
+ * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
+ * needs with ww_mutex_lock. Note that the -EALREADY return code from
+ * ww_mutex_lock can be used to avoid locking this contended mutex twice.
+ *
+ * It is forbidden to call this function with any other w/w mutexes associated
+ * with the context held. It is forbidden to call this on anything else than the
+ * contending mutex.
+ *
+ * Note that the slowpath lock acquiring can also be done by calling
+ * ww_mutex_lock directly. This function here is simply to help w/w mutex
+ * locking code readability by clearly denoting the slowpath.
+ */
+static inline void
+ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+{
+	int ret;
+#ifdef CONFIG_DEBUG_MUTEXES
+	DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
+#endif
+	ret = ww_mutex_lock(lock, ctx);
+	(void)ret;
+}
+
+/**
+ * ww_mutex_lock_slow_interruptible - slowpath acquiring of the w/w mutex,
+ * 				      interruptible
+ * @lock: the mutex to be acquired
+ * @ctx: w/w acquire context
+ *
+ * Acquires a w/w mutex with the given context after a wound case. This function
+ * will sleep until the lock becomes available and returns 0 when the lock has
+ * been acquired. If a signal arrives while waiting for the lock then this
+ * function returns -EINTR.
+ *
+ * The caller must have released all w/w mutexes already acquired with the
+ * context and then call this function on the contended lock.
+ *
+ * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
+ * needs with ww_mutex_lock. Note that the -EALREADY return code from
+ * ww_mutex_lock can be used to avoid locking this contended mutex twice.
+ *
+ * It is forbidden to call this function with any other w/w mutexes associated
+ * with the given context held. It is forbidden to call this on anything else
+ * than the contending mutex.
+ *
+ * Note that the slowpath lock acquiring can also be done by calling
+ * ww_mutex_lock_interruptible directly. This function here is simply to help
+ * w/w mutex locking code readability by clearly denoting the slowpath.
+ */
+static inline int __must_check
+ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,
+				 struct ww_acquire_ctx *ctx)
+{
+#ifdef CONFIG_DEBUG_MUTEXES
+	DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);
+#endif
+	return ww_mutex_lock_interruptible(lock, ctx);
+}
+
+extern void ww_mutex_unlock(struct ww_mutex *lock);
+
+/**
+ * ww_mutex_trylock - tries to acquire the w/w mutex without acquire context
+ * @lock: mutex to lock
+ *
+ * Trylocks a mutex without acquire context, so no deadlock detection is
+ * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
+ */
+static inline int __must_check ww_mutex_trylock(struct ww_mutex *lock)
+{
+	return mutex_trylock(&lock->base);
+}
+
+/***
+ * ww_mutex_destroy - mark a w/w mutex unusable
+ * @lock: the mutex to be destroyed
+ *
+ * This function marks the mutex uninitialized, and any subsequent
+ * use of the mutex is forbidden. The mutex must not be locked when
+ * this function is called.
+ */
+static inline void ww_mutex_destroy(struct ww_mutex *lock)
+{
+	mutex_destroy(&lock->base);
+}
+
+/**
+ * ww_mutex_is_locked - is the w/w mutex locked
+ * @lock: the mutex to be queried
+ *
+ * Returns 1 if the mutex is locked, 0 if unlocked.
+ */
+static inline bool ww_mutex_is_locked(struct ww_mutex *lock)
+{
+	return mutex_is_locked(&lock->base);
+}
+
 extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 
 #ifndef CONFIG_HAVE_ARCH_MUTEX_CPU_RELAX