backlight: atmel-pwm-bl: refactor gpio_on handling

[linux-2.6.git] / drivers / md / bcache / closure.h

#ifndef _LINUX_CLOSURE_H
#define _LINUX_CLOSURE_H

#include <linux/llist.h>
#include <linux/sched.h>
#include <linux/workqueue.h>

/*
 * Closure is perhaps the most overused and abused term in computer science, but
 * since I've been unable to come up with anything better you're stuck with it
 * again.
 *
 * What are closures?
 *
 * They embed a refcount. The basic idea is they count "things that are in
 * progress" - in flight bios, some other thread that's doing something else -
 * anything you might want to wait on.
 *
 * The refcount may be manipulated with closure_get() and closure_put().
 * closure_put() is where many of the interesting things happen, when it causes
 * the refcount to go to 0.
 *
 * Closures can be used to wait on things both synchronously and asynchronously,
 * and synchronous and asynchronous use can be mixed without restriction. To
 * wait synchronously, use closure_sync() - you will sleep until your closure's
 * refcount hits 1.
 *
 * To wait asynchronously, use
 *   continue_at(cl, next_function, workqueue);
 *
 * passing it, as you might expect, the function to run when nothing is pending
 * and the workqueue to run that function out of.
 *
 * continue_at() also, critically, is a macro that returns the calling function.
 * There's good reason for this.
 *
 * To use safely closures asynchronously, they must always have a refcount while
 * they are running owned by the thread that is running them. Otherwise, suppose
 * you submit some bios and wish to have a function run when they all complete:
 *
 * foo_endio(struct bio *bio, int error)
 * {
 *      closure_put(cl);
 * }
 *
 * closure_init(cl);
 *
 * do_stuff();
 * closure_get(cl);
 * bio1->bi_endio = foo_endio;
 * bio_submit(bio1);
 *
 * do_more_stuff();
 * closure_get(cl);
 * bio2->bi_endio = foo_endio;
 * bio_submit(bio2);
 *
 * continue_at(cl, complete_some_read, system_wq);
 *
 * If closure's refcount started at 0, complete_some_read() could run before the
 * second bio was submitted - which is almost always not what you want! More
 * importantly, it wouldn't be possible to say whether the original thread or
 * complete_some_read()'s thread owned the closure - and whatever state it was
 * associated with!
 *
 * So, closure_init() initializes a closure's refcount to 1 - and when a
 * closure_fn is run, the refcount will be reset to 1 first.
 *
 * Then, the rule is - if you got the refcount with closure_get(), release it
 * with closure_put() (i.e, in a bio->bi_endio function). If you have a refcount
 * on a closure because you called closure_init() or you were run out of a
 * closure - _always_ use continue_at(). Doing so consistently will help
 * eliminate an entire class of particularly pernicious races.
 *
 * For a closure to wait on an arbitrary event, we need to introduce waitlists:
 *
 * struct closure_waitlist list;
 * closure_wait_event(list, cl, condition);
 * closure_wake_up(wait_list);
 *
 * These work analagously to wait_event() and wake_up() - except that instead of
 * operating on the current thread (for wait_event()) and lists of threads, they
 * operate on an explicit closure and lists of closures.
 *
 * Because it's a closure we can now wait either synchronously or
 * asynchronously. closure_wait_event() returns the current value of the
 * condition, and if it returned false continue_at() or closure_sync() can be
 * used to wait for it to become true.
 *
 * It's useful for waiting on things when you can't sleep in the context in
 * which you must check the condition (perhaps a spinlock held, or you might be
 * beneath generic_make_request() - in which case you can't sleep on IO).
 *
 * closure_wait_event() will wait either synchronously or asynchronously,
 * depending on whether the closure is in blocking mode or not. You can pick a
 * mode explicitly with closure_wait_event_sync() and
 * closure_wait_event_async(), which do just what you might expect.
 *
 * Lastly, you might have a wait list dedicated to a specific event, and have no
 * need for specifying the condition - you just want to wait until someone runs
 * closure_wake_up() on the appropriate wait list. In that case, just use
 * closure_wait(). It will return either true or false, depending on whether the
 * closure was already on a wait list or not - a closure can only be on one wait
 * list at a time.
 *
 * Parents:
 *
 * closure_init() takes two arguments - it takes the closure to initialize, and
 * a (possibly null) parent.
 *
 * If parent is non null, the new closure will have a refcount for its lifetime;
 * a closure is considered to be "finished" when its refcount hits 0 and the
 * function to run is null. Hence
 *
 * continue_at(cl, NULL, NULL);
 *
 * returns up the (spaghetti) stack of closures, precisely like normal return
 * returns up the C stack. continue_at() with non null fn is better thought of
 * as doing a tail call.
 *
 * All this implies that a closure should typically be embedded in a particular
 * struct (which its refcount will normally control the lifetime of), and that
 * struct can very much be thought of as a stack frame.
 *
 * Locking:
 *
 * Closures are based on work items but they can be thought of as more like
 * threads - in that like threads and unlike work items they have a well
 * defined lifetime; they are created (with closure_init()) and eventually
 * complete after a continue_at(cl, NULL, NULL).
 *
 * Suppose you've got some larger structure with a closure embedded in it that's
 * used for periodically doing garbage collection. You only want one garbage
 * collection happening at a time, so the natural thing to do is protect it with
 * a lock. However, it's difficult to use a lock protecting a closure correctly
 * because the unlock should come after the last continue_to() (additionally, if
 * you're using the closure asynchronously a mutex won't work since a mutex has
 * to be unlocked by the same process that locked it).
 *
 * So to make it less error prone and more efficient, we also have the ability
 * to use closures as locks:
 *
 * closure_init_unlocked();
 * closure_trylock();
 *
 * That's all we need for trylock() - the last closure_put() implicitly unlocks
 * it for you.  But for closure_lock(), we also need a wait list:
 *
 * struct closure_with_waitlist frobnicator_cl;
 *
 * closure_init_unlocked(&frobnicator_cl);
 * closure_lock(&frobnicator_cl);
 *
 * A closure_with_waitlist embeds a closure and a wait list - much like struct
 * delayed_work embeds a work item and a timer_list. The important thing is, use
 * it exactly like you would a regular closure and closure_put() will magically
 * handle everything for you.
 *
 * We've got closures that embed timers, too. They're called, appropriately
 * enough:
 * struct closure_with_timer;
 *
 * This gives you access to closure_delay(). It takes a refcount for a specified
 * number of jiffies - you could then call closure_sync() (for a slightly
 * convoluted version of msleep()) or continue_at() - which gives you the same
 * effect as using a delayed work item, except you can reuse the work_struct
 * already embedded in struct closure.
 *
 * Lastly, there's struct closure_with_waitlist_and_timer. It does what you
 * probably expect, if you happen to need the features of both. (You don't
 * really want to know how all this is implemented, but if I've done my job
 * right you shouldn't have to care).
 */

struct closure;
typedef void (closure_fn) (struct closure *);

struct closure_waitlist {
        struct llist_head       list;
};

enum closure_type {
        TYPE_closure                            = 0,
        TYPE_closure_with_waitlist              = 1,
        TYPE_closure_with_timer                 = 2,
        TYPE_closure_with_waitlist_and_timer    = 3,
        MAX_CLOSURE_TYPE                        = 3,
};

enum closure_state {
        /*
         * CLOSURE_BLOCKING: Causes closure_wait_event() to block, instead of
         * waiting asynchronously
         *
         * CLOSURE_WAITING: Set iff the closure is on a waitlist. Must be set by
         * the thread that owns the closure, and cleared by the thread that's
         * waking up the closure.
         *
         * CLOSURE_SLEEPING: Must be set before a thread uses a closure to sleep
         * - indicates that cl->task is valid and closure_put() may wake it up.
         * Only set or cleared by the thread that owns the closure.
         *
         * CLOSURE_TIMER: Analagous to CLOSURE_WAITING, indicates that a closure
         * has an outstanding timer. Must be set by the thread that owns the
         * closure, and cleared by the timer function when the timer goes off.
         *
         * The rest are for debugging and don't affect behaviour:
         *
         * CLOSURE_RUNNING: Set when a closure is running (i.e. by
         * closure_init() and when closure_put() runs then next function), and
         * must be cleared before remaining hits 0. Primarily to help guard
         * against incorrect usage and accidentally transferring references.
         * continue_at() and closure_return() clear it for you, if you're doing
         * something unusual you can use closure_set_dead() which also helps
         * annotate where references are being transferred.
         *
         * CLOSURE_STACK: Sanity check - remaining should never hit 0 on a
         * closure with this flag set
         */

        CLOSURE_BITS_START      = (1 << 19),
        CLOSURE_DESTRUCTOR      = (1 << 19),
        CLOSURE_BLOCKING        = (1 << 21),
        CLOSURE_WAITING         = (1 << 23),
        CLOSURE_SLEEPING        = (1 << 25),
        CLOSURE_TIMER           = (1 << 27),
        CLOSURE_RUNNING         = (1 << 29),
        CLOSURE_STACK           = (1 << 31),
};

#define CLOSURE_GUARD_MASK                                      \
        ((CLOSURE_DESTRUCTOR|CLOSURE_BLOCKING|CLOSURE_WAITING|  \
          CLOSURE_SLEEPING|CLOSURE_TIMER|CLOSURE_RUNNING|CLOSURE_STACK) << 1)

#define CLOSURE_REMAINING_MASK          (CLOSURE_BITS_START - 1)
#define CLOSURE_REMAINING_INITIALIZER   (1|CLOSURE_RUNNING)

struct closure {
        union {
                struct {
                        struct workqueue_struct *wq;
                        struct task_struct      *task;
                        struct llist_node       list;
                        closure_fn              *fn;
                };
                struct work_struct      work;
        };

        struct closure          *parent;

        atomic_t                remaining;

        enum closure_type       type;

#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
#define CLOSURE_MAGIC_DEAD      0xc054dead
#define CLOSURE_MAGIC_ALIVE     0xc054a11e

        unsigned                magic;
        struct list_head        all;
        unsigned long           ip;
        unsigned long           waiting_on;
#endif
};

struct closure_with_waitlist {
        struct closure          cl;
        struct closure_waitlist wait;
};

struct closure_with_timer {
        struct closure          cl;
        struct timer_list       timer;
};

struct closure_with_waitlist_and_timer {
        struct closure          cl;
        struct closure_waitlist wait;
        struct timer_list       timer;
};

extern unsigned invalid_closure_type(void);

#define __CLOSURE_TYPE(cl, _t)                                          \
          __builtin_types_compatible_p(typeof(cl), struct _t)           \
                ? TYPE_ ## _t :                                         \

#define __closure_type(cl)                                              \
(                                                                       \
        __CLOSURE_TYPE(cl, closure)                                     \
        __CLOSURE_TYPE(cl, closure_with_waitlist)                       \
        __CLOSURE_TYPE(cl, closure_with_timer)                          \
        __CLOSURE_TYPE(cl, closure_with_waitlist_and_timer)             \
        invalid_closure_type()                                          \
)

void closure_sub(struct closure *cl, int v);
void closure_put(struct closure *cl);
void closure_queue(struct closure *cl);
void __closure_wake_up(struct closure_waitlist *list);
bool closure_wait(struct closure_waitlist *list, struct closure *cl);
void closure_sync(struct closure *cl);

bool closure_trylock(struct closure *cl, struct closure *parent);
void __closure_lock(struct closure *cl, struct closure *parent,
                    struct closure_waitlist *wait_list);

void do_closure_timer_init(struct closure *cl);
bool __closure_delay(struct closure *cl, unsigned long delay,
                     struct timer_list *timer);
void __closure_flush(struct closure *cl, struct timer_list *timer);
void __closure_flush_sync(struct closure *cl, struct timer_list *timer);

#ifdef CONFIG_BCACHE_CLOSURES_DEBUG

void closure_debug_init(void);
void closure_debug_create(struct closure *cl);
void closure_debug_destroy(struct closure *cl);

#else

static inline void closure_debug_init(void) {}
static inline void closure_debug_create(struct closure *cl) {}
static inline void closure_debug_destroy(struct closure *cl) {}

#endif

static inline void closure_set_ip(struct closure *cl)
{
#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
        cl->ip = _THIS_IP_;
#endif
}

static inline void closure_set_ret_ip(struct closure *cl)
{
#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
        cl->ip = _RET_IP_;
#endif
}

static inline void closure_get(struct closure *cl)
{
#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
        BUG_ON((atomic_inc_return(&cl->remaining) &
                CLOSURE_REMAINING_MASK) <= 1);
#else
        atomic_inc(&cl->remaining);
#endif
}

static inline void closure_set_stopped(struct closure *cl)
{
        atomic_sub(CLOSURE_RUNNING, &cl->remaining);
}

static inline bool closure_is_stopped(struct closure *cl)
{
        return !(atomic_read(&cl->remaining) & CLOSURE_RUNNING);
}

static inline bool closure_is_unlocked(struct closure *cl)
{
        return atomic_read(&cl->remaining) == -1;
}

static inline void do_closure_init(struct closure *cl, struct closure *parent,
                                   bool running)
{
        switch (cl->type) {
        case TYPE_closure_with_timer:
        case TYPE_closure_with_waitlist_and_timer:
                do_closure_timer_init(cl);
        default:
                break;
        }

        cl->parent = parent;
        if (parent)
                closure_get(parent);

        if (running) {
                closure_debug_create(cl);
                atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
        } else
                atomic_set(&cl->remaining, -1);

        closure_set_ip(cl);
}

/*
 * Hack to get at the embedded closure if there is one, by doing an unsafe cast:
 * the result of __closure_type() is thrown away, it's used merely for type
 * checking.
 */
#define __to_internal_closure(cl)                               \
({                                                              \
        BUILD_BUG_ON(__closure_type(*cl) > MAX_CLOSURE_TYPE);   \
        (struct closure *) cl;                                  \
})

#define closure_init_type(cl, parent, running)                  \
do {                                                            \
        struct closure *_cl = __to_internal_closure(cl);        \
        _cl->type = __closure_type(*(cl));                      \
        do_closure_init(_cl, parent, running);                  \
} while (0)

/**
 * __closure_init() - Initialize a closure, skipping the memset()
 *
 * May be used instead of closure_init() when memory has already been zeroed.
 */
#define __closure_init(cl, parent)                              \
        closure_init_type(cl, parent, true)

/**
 * closure_init() - Initialize a closure, setting the refcount to 1
 * @cl:         closure to initialize
 * @parent:     parent of the new closure. cl will take a refcount on it for its
 *              lifetime; may be NULL.
 */
#define closure_init(cl, parent)                                \
do {                                                            \
        memset((cl), 0, sizeof(*(cl)));                         \
        __closure_init(cl, parent);                             \
} while (0)

static inline void closure_init_stack(struct closure *cl)
{
        memset(cl, 0, sizeof(struct closure));
        atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER|
                   CLOSURE_BLOCKING|CLOSURE_STACK);
}

/**
 * closure_init_unlocked() - Initialize a closure but leave it unlocked.
 * @cl:         closure to initialize
 *
 * For when the closure will be used as a lock. The closure may not be used
 * until after a closure_lock() or closure_trylock().
 */
#define closure_init_unlocked(cl)                               \
do {                                                            \
        memset((cl), 0, sizeof(*(cl)));                         \
        closure_init_type(cl, NULL, false);                     \
} while (0)

/**
 * closure_lock() - lock and initialize a closure.
 * @cl:         the closure to lock
 * @parent:     the new parent for this closure
 *
 * The closure must be of one of the types that has a waitlist (otherwise we
 * wouldn't be able to sleep on contention).
 *
 * @parent has exactly the same meaning as in closure_init(); if non null, the
 * closure will take a reference on @parent which will be released when it is
 * unlocked.
 */
#define closure_lock(cl, parent)                                \
        __closure_lock(__to_internal_closure(cl), parent, &(cl)->wait)

/**
 * closure_delay() - delay some number of jiffies
 * @cl:         the closure that will sleep
 * @delay:      the delay in jiffies
 *
 * Takes a refcount on @cl which will be released after @delay jiffies; this may
 * be used to have a function run after a delay with continue_at(), or
 * closure_sync() may be used for a convoluted version of msleep().
 */
#define closure_delay(cl, delay)                        \
        __closure_delay(__to_internal_closure(cl), delay, &(cl)->timer)

#define closure_flush(cl)                               \
        __closure_flush(__to_internal_closure(cl), &(cl)->timer)

#define closure_flush_sync(cl)                          \
        __closure_flush_sync(__to_internal_closure(cl), &(cl)->timer)

static inline void __closure_end_sleep(struct closure *cl)
{
        __set_current_state(TASK_RUNNING);

        if (atomic_read(&cl->remaining) & CLOSURE_SLEEPING)
                atomic_sub(CLOSURE_SLEEPING, &cl->remaining);
}

static inline void __closure_start_sleep(struct closure *cl)
{
        closure_set_ip(cl);
        cl->task = current;
        set_current_state(TASK_UNINTERRUPTIBLE);

        if (!(atomic_read(&cl->remaining) & CLOSURE_SLEEPING))
                atomic_add(CLOSURE_SLEEPING, &cl->remaining);
}

/**
 * closure_blocking() - returns true if the closure is in blocking mode.
 *
 * If a closure is in blocking mode, closure_wait_event() will sleep until the
 * condition is true instead of waiting asynchronously.
 */
static inline bool closure_blocking(struct closure *cl)
{
        return atomic_read(&cl->remaining) & CLOSURE_BLOCKING;
}

/**
 * set_closure_blocking() - put a closure in blocking mode.
 *
 * If a closure is in blocking mode, closure_wait_event() will sleep until the
 * condition is true instead of waiting asynchronously.
 *
 * Not thread safe - can only be called by the thread running the closure.
 */
static inline void set_closure_blocking(struct closure *cl)
{
        if (!closure_blocking(cl))
                atomic_add(CLOSURE_BLOCKING, &cl->remaining);
}

/*
 * Not thread safe - can only be called by the thread running the closure.
 */
static inline void clear_closure_blocking(struct closure *cl)
{
        if (closure_blocking(cl))
                atomic_sub(CLOSURE_BLOCKING, &cl->remaining);
}

/**
 * closure_wake_up() - wake up all closures on a wait list.
 */
static inline void closure_wake_up(struct closure_waitlist *list)
{
        smp_mb();
        __closure_wake_up(list);
}

/*
 * Wait on an event, synchronously or asynchronously - analogous to wait_event()
 * but for closures.
 *
 * The loop is oddly structured so as to avoid a race; we must check the
 * condition again after we've added ourself to the waitlist. We know if we were
 * already on the waitlist because closure_wait() returns false; thus, we only
 * schedule or break if closure_wait() returns false. If it returns true, we
 * just loop again - rechecking the condition.
 *
 * The __closure_wake_up() is necessary because we may race with the event
 * becoming true; i.e. we see event false -> wait -> recheck condition, but the
 * thread that made the event true may have called closure_wake_up() before we
 * added ourself to the wait list.
 *
 * We have to call closure_sync() at the end instead of just
 * __closure_end_sleep() because a different thread might've called
 * closure_wake_up() before us and gotten preempted before they dropped the
 * refcount on our closure. If this was a stack allocated closure, that would be
 * bad.
 */
#define __closure_wait_event(list, cl, condition, _block)               \
({                                                                      \
        bool block = _block;                                            \
        typeof(condition) ret;                                          \
                                                                        \
        while (1) {                                                     \
                ret = (condition);                                      \
                if (ret) {                                              \
                        __closure_wake_up(list);                        \
                        if (block)                                      \
                                closure_sync(cl);                       \
                                                                        \
                        break;                                          \
                }                                                       \
                                                                        \
                if (block)                                              \
                        __closure_start_sleep(cl);                      \
                                                                        \
                if (!closure_wait(list, cl)) {                          \
                        if (!block)                                     \
                                break;                                  \
                                                                        \
                        schedule();                                     \
                }                                                       \
        }                                                               \
                                                                        \
        ret;                                                            \
})

/**
 * closure_wait_event() - wait on a condition, synchronously or asynchronously.
 * @list:       the wait list to wait on
 * @cl:         the closure that is doing the waiting
 * @condition:  a C expression for the event to wait for
 *
 * If the closure is in blocking mode, sleeps until the @condition evaluates to
 * true - exactly like wait_event().
 *
 * If the closure is not in blocking mode, waits asynchronously; if the
 * condition is currently false the @cl is put onto @list and returns. @list
 * owns a refcount on @cl; closure_sync() or continue_at() may be used later to
 * wait for another thread to wake up @list, which drops the refcount on @cl.
 *
 * Returns the value of @condition; @cl will be on @list iff @condition was
 * false.
 *
 * closure_wake_up(@list) must be called after changing any variable that could
 * cause @condition to become true.
 */
#define closure_wait_event(list, cl, condition)                         \
        __closure_wait_event(list, cl, condition, closure_blocking(cl))

#define closure_wait_event_async(list, cl, condition)                   \
        __closure_wait_event(list, cl, condition, false)

#define closure_wait_event_sync(list, cl, condition)                    \
        __closure_wait_event(list, cl, condition, true)

static inline void set_closure_fn(struct closure *cl, closure_fn *fn,
                                  struct workqueue_struct *wq)
{
        BUG_ON(object_is_on_stack(cl));
        closure_set_ip(cl);
        cl->fn = fn;
        cl->wq = wq;
        /* between atomic_dec() in closure_put() */
        smp_mb__before_atomic_dec();
}

#define continue_at(_cl, _fn, _wq)                                      \
do {                                                                    \
        set_closure_fn(_cl, _fn, _wq);                                  \
        closure_sub(_cl, CLOSURE_RUNNING + 1);                          \
        return;                                                         \
} while (0)

#define closure_return(_cl)     continue_at((_cl), NULL, NULL)

#define continue_at_nobarrier(_cl, _fn, _wq)                            \
do {                                                                    \
        set_closure_fn(_cl, _fn, _wq);                                  \
        closure_queue(cl);                                              \
        return;                                                         \
} while (0)

#define closure_return_with_destructor(_cl, _destructor)                \
do {                                                                    \
        set_closure_fn(_cl, _destructor, NULL);                         \
        closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1);     \
        return;                                                         \
} while (0)

static inline void closure_call(struct closure *cl, closure_fn fn,
                                struct workqueue_struct *wq,
                                struct closure *parent)
{
        closure_init(cl, parent);
        continue_at_nobarrier(cl, fn, wq);
}

static inline void closure_trylock_call(struct closure *cl, closure_fn fn,
                                        struct workqueue_struct *wq,
                                        struct closure *parent)
{
        if (closure_trylock(cl, parent))
                continue_at_nobarrier(cl, fn, wq);
}

#endif /* _LINUX_CLOSURE_H */