2 files changed, 355 insertions, 1 deletions

diff --git a/include/linux/mutex-debug.h b/include/linux/mutex-debug.h
index 731d77d6e155..4ac8b1977b73 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 433da8a1a426..a56b0ccc8a6c 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