#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 */
