[PATCH] mutex subsystem, core

mutex implementation, core files: just the basic subsystem, no users of it.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@infradead.org>

3 files changed, 361 insertions, 1 deletions

diff --git a/kernel/Makefile b/kernel/Makefile
index 4f5a1453093..de580b4d54a 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -7,7 +7,7 @@ obj-y     = sched.o fork.o exec_domain.o panic.o printk.o profile.o \
             sysctl.o capability.o ptrace.o timer.o user.o \
             signal.o sys.o kmod.o workqueue.o pid.o \
             rcupdate.o intermodule.o extable.o params.o posix-timers.o \
-            kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o
+            kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o
 
 obj-$(CONFIG_FUTEX) += futex.o
 obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o
diff --git a/kernel/mutex.c b/kernel/mutex.c
new file mode 100644
index 00000000000..7eb96066144
--- /dev/null
+++ b/kernel/mutex.c
@@ -0,0 +1,325 @@
+/*
+ * kernel/mutex.c
+ *
+ * Mutexes: blocking mutual exclusion locks
+ *
+ * Started by Ingo Molnar:
+ *
+ *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
+ *
+ * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
+ * David Howells for suggestions and improvements.
+ *
+ * Also see Documentation/mutex-design.txt.
+ */
+#include <linux/mutex.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+#include <linux/spinlock.h>
+#include <linux/interrupt.h>
+
+/*
+ * In the DEBUG case we are using the "NULL fastpath" for mutexes,
+ * which forces all calls into the slowpath:
+ */
+#ifdef CONFIG_DEBUG_MUTEXES
+# include "mutex-debug.h"
+# include <asm-generic/mutex-null.h>
+#else
+# include "mutex.h"
+# include <asm/mutex.h>
+#endif
+
+/***
+ * mutex_init - initialize the mutex
+ * @lock: the mutex to be initialized
+ *
+ * Initialize the mutex to unlocked state.
+ *
+ * It is not allowed to initialize an already locked mutex.
+ */
+void fastcall __mutex_init(struct mutex *lock, const char *name)
+{
+        atomic_set(&lock->count, 1);
+        spin_lock_init(&lock->wait_lock);
+        INIT_LIST_HEAD(&lock->wait_list);
+
+        debug_mutex_init(lock, name);
+}
+
+EXPORT_SYMBOL(__mutex_init);
+
+/*
+ * We split the mutex lock/unlock logic into separate fastpath and
+ * slowpath functions, to reduce the register pressure on the fastpath.
+ * We also put the fastpath first in the kernel image, to make sure the
+ * branch is predicted by the CPU as default-untaken.
+ */
+static void fastcall noinline __sched
+__mutex_lock_slowpath(atomic_t *lock_count __IP_DECL__);
+
+/***
+ * mutex_lock - acquire the mutex
+ * @lock: the mutex to be acquired
+ *
+ * Lock the mutex exclusively for this task. If the mutex is not
+ * available right now, it will sleep until it can get it.
+ *
+ * The mutex must later on be released by the same task that
+ * acquired it. Recursive locking is not allowed. The task
+ * may not exit without first unlocking the mutex. Also, kernel
+ * memory where the mutex resides mutex 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 CONFIG_DEBUG_MUTEXES .config option turns on debugging
+ *   checks that will enforce the restrictions and will also do
+ *   deadlock debugging. )
+ *
+ * This function is similar to (but not equivalent to) down().
+ */
+void fastcall __sched mutex_lock(struct mutex *lock)
+{
+        /*
+         * The locking fastpath is the 1->0 transition from
+         * 'unlocked' into 'locked' state.
+         *
+         * NOTE: if asm/mutex.h is included, then some architectures
+         * rely on mutex_lock() having _no other code_ here but this
+         * fastpath. That allows the assembly fastpath to do
+         * tail-merging optimizations. (If you want to put testcode
+         * here, do it under #ifndef CONFIG_MUTEX_DEBUG.)
+         */
+        __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
+}
+
+EXPORT_SYMBOL(mutex_lock);
+
+static void fastcall noinline __sched
+__mutex_unlock_slowpath(atomic_t *lock_count __IP_DECL__);
+
+/***
+ * mutex_unlock - release the mutex
+ * @lock: the mutex to be released
+ *
+ * Unlock a mutex that has been locked by this task previously.
+ *
+ * This function must not be used in interrupt context. Unlocking
+ * of a not locked mutex is not allowed.
+ *
+ * This function is similar to (but not equivalent to) up().
+ */
+void fastcall __sched mutex_unlock(struct mutex *lock)
+{
+        /*
+         * The unlocking fastpath is the 0->1 transition from 'locked'
+         * into 'unlocked' state:
+         *
+         * NOTE: no other code must be here - see mutex_lock() .
+         */
+        __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
+}
+
+EXPORT_SYMBOL(mutex_unlock);
+
+/*
+ * Lock a mutex (possibly interruptible), slowpath:
+ */
+static inline int __sched
+__mutex_lock_common(struct mutex *lock, long state __IP_DECL__)
+{
+        struct task_struct *task = current;
+        struct mutex_waiter waiter;
+        unsigned int old_val;
+
+        debug_mutex_init_waiter(&waiter);
+
+        spin_lock_mutex(&lock->wait_lock);
+
+        debug_mutex_add_waiter(lock, &waiter, task->thread_info, ip);
+
+        /* add waiting tasks to the end of the waitqueue (FIFO): */
+        list_add_tail(&waiter.list, &lock->wait_list);
+        waiter.task = task;
+
+        for (;;) {
+                /*
+                 * Lets try to take the lock again - this is needed even if
+                 * we get here for the first time (shortly after failing to
+                 * acquire the lock), to make sure that we get a wakeup once
+                 * it's unlocked. Later on, if we sleep, this is the
+                 * operation that gives us the lock. We xchg it to -1, so
+                 * that when we release the lock, we properly wake up the
+                 * other waiters:
+                 */
+                old_val = atomic_xchg(&lock->count, -1);
+                if (old_val == 1)
+                        break;
+
+                /*
+                 * got a signal? (This code gets eliminated in the
+                 * TASK_UNINTERRUPTIBLE case.)
+                 */
+                if (unlikely(state == TASK_INTERRUPTIBLE &&
+                                                signal_pending(task))) {
+                        mutex_remove_waiter(lock, &waiter, task->thread_info);
+                        spin_unlock_mutex(&lock->wait_lock);
+
+                        debug_mutex_free_waiter(&waiter);
+                        return -EINTR;
+                }
+                __set_task_state(task, state);
+
+                /* didnt get the lock, go to sleep: */
+                spin_unlock_mutex(&lock->wait_lock);
+                schedule();
+                spin_lock_mutex(&lock->wait_lock);
+        }
+
+        /* got the lock - rejoice! */
+        mutex_remove_waiter(lock, &waiter, task->thread_info);
+        debug_mutex_set_owner(lock, task->thread_info __IP__);
+
+        /* set it to 0 if there are no waiters left: */
+        if (likely(list_empty(&lock->wait_list)))
+                atomic_set(&lock->count, 0);
+
+        spin_unlock_mutex(&lock->wait_lock);
+
+        debug_mutex_free_waiter(&waiter);
+
+        DEBUG_WARN_ON(list_empty(&lock->held_list));
+        DEBUG_WARN_ON(lock->owner != task->thread_info);
+
+        return 0;
+}
+
+static void fastcall noinline __sched
+__mutex_lock_slowpath(atomic_t *lock_count __IP_DECL__)
+{
+        struct mutex *lock = container_of(lock_count, struct mutex, count);
+
+        __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE __IP__);
+}
+
+/*
+ * Release the lock, slowpath:
+ */
+static fastcall noinline void
+__mutex_unlock_slowpath(atomic_t *lock_count __IP_DECL__)
+{
+        struct mutex *lock = container_of(lock_count, struct mutex, count);
+
+        DEBUG_WARN_ON(lock->owner != current_thread_info());
+
+        spin_lock_mutex(&lock->wait_lock);
+
+        /*
+         * some architectures leave the lock unlocked in the fastpath failure
+         * case, others need to leave it locked. In the later case we have to
+         * unlock it here
+         */
+        if (__mutex_slowpath_needs_to_unlock())
+                atomic_set(&lock->count, 1);
+
+        debug_mutex_unlock(lock);
+
+        if (!list_empty(&lock->wait_list)) {
+                /* get the first entry from the wait-list: */
+                struct mutex_waiter *waiter =
+                                list_entry(lock->wait_list.next,
+                                           struct mutex_waiter, list);
+
+                debug_mutex_wake_waiter(lock, waiter);
+
+                wake_up_process(waiter->task);
+        }
+
+        debug_mutex_clear_owner(lock);
+
+        spin_unlock_mutex(&lock->wait_lock);
+}
+
+/*
+ * Here come the less common (and hence less performance-critical) APIs:
+ * mutex_lock_interruptible() and mutex_trylock().
+ */
+static int fastcall noinline __sched
+__mutex_lock_interruptible_slowpath(atomic_t *lock_count __IP_DECL__);
+
+/***
+ * mutex_lock_interruptible - acquire the mutex, interruptable
+ * @lock: the mutex to be acquired
+ *
+ * Lock the mutex like mutex_lock(), and return 0 if the mutex has
+ * been acquired or sleep until the mutex becomes available. If a
+ * signal arrives while waiting for the lock then this function
+ * returns -EINTR.
+ *
+ * This function is similar to (but not equivalent to) down_interruptible().
+ */
+int fastcall __sched mutex_lock_interruptible(struct mutex *lock)
+{
+        /* NOTE: no other code must be here - see mutex_lock() */
+        return __mutex_fastpath_lock_retval
+                        (&lock->count, __mutex_lock_interruptible_slowpath);
+}
+
+EXPORT_SYMBOL(mutex_lock_interruptible);
+
+static int fastcall noinline __sched
+__mutex_lock_interruptible_slowpath(atomic_t *lock_count __IP_DECL__)
+{
+        struct mutex *lock = container_of(lock_count, struct mutex, count);
+
+        return __mutex_lock_common(lock, TASK_INTERRUPTIBLE __IP__);
+}
+
+/*
+ * Spinlock based trylock, we take the spinlock and check whether we
+ * can get the lock:
+ */
+static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
+{
+        struct mutex *lock = container_of(lock_count, struct mutex, count);
+        int prev;
+
+        spin_lock_mutex(&lock->wait_lock);
+
+        prev = atomic_xchg(&lock->count, -1);
+        if (likely(prev == 1))
+                debug_mutex_set_owner(lock, current_thread_info() __RET_IP__);
+        /* Set it back to 0 if there are no waiters: */
+        if (likely(list_empty(&lock->wait_list)))
+                atomic_set(&lock->count, 0);
+
+        spin_unlock_mutex(&lock->wait_lock);
+
+        return prev == 1;
+}
+
+/***
+ * mutex_trylock - try acquire the mutex, without waiting
+ * @lock: the mutex to be acquired
+ *
+ * Try to acquire the mutex atomically. Returns 1 if the mutex
+ * has been acquired successfully, and 0 on contention.
+ *
+ * NOTE: this function follows the spin_trylock() convention, so
+ * it is negated to the down_trylock() return values! Be careful
+ * about this when converting semaphore users to mutexes.
+ *
+ * This function must not be used in interrupt context. The
+ * mutex must be released by the same task that acquired it.
+ */
+int fastcall mutex_trylock(struct mutex *lock)
+{
+        return __mutex_fastpath_trylock(&lock->count,
+                                        __mutex_trylock_slowpath);
+}
+
+EXPORT_SYMBOL(mutex_trylock);
+
+
+
diff --git a/kernel/mutex.h b/kernel/mutex.h
new file mode 100644
index 00000000000..00fe84e7b67
--- /dev/null
+++ b/kernel/mutex.h
@@ -0,0 +1,35 @@
+/*
+ * Mutexes: blocking mutual exclusion locks
+ *
+ * started by Ingo Molnar:
+ *
+ *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
+ *
+ * This file contains mutex debugging related internal prototypes, for the
+ * !CONFIG_DEBUG_MUTEXES case. Most of them are NOPs:
+ */
+
+#define spin_lock_mutex(lock)                   spin_lock(lock)
+#define spin_unlock_mutex(lock)                 spin_unlock(lock)
+#define mutex_remove_waiter(lock, waiter, ti) \
+                __list_del((waiter)->list.prev, (waiter)->list.next)
+
+#define DEBUG_WARN_ON(c)                                do { } while (0)
+#define debug_mutex_set_owner(lock, new_owner)          do { } while (0)
+#define debug_mutex_clear_owner(lock)                   do { } while (0)
+#define debug_mutex_init_waiter(waiter)                 do { } while (0)
+#define debug_mutex_wake_waiter(lock, waiter)           do { } while (0)
+#define debug_mutex_free_waiter(waiter)                 do { } while (0)
+#define debug_mutex_add_waiter(lock, waiter, ti, ip)    do { } while (0)
+#define debug_mutex_unlock(lock)                        do { } while (0)
+#define debug_mutex_init(lock, name)                    do { } while (0)
+
+/*
+ * Return-address parameters/declarations. They are very useful for
+ * debugging, but add overhead in the !DEBUG case - so we go the
+ * trouble of using this not too elegant but zero-cost solution:
+ */
+#define __IP_DECL__
+#define __IP__
+#define __RET_IP__
+