/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_CLOSURE_H
#define _LINUX_CLOSURE_H
#include <linux/llist.h>
#include <linux/sched.h>
#include <linux/sched/task_stack.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, requires a 'return' immediately following the
* location where this macro is referenced, to return to 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)
* {
* 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.
*
* 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.
*/
struct closure;
struct closure_syncer;
typedef void (closure_fn) (struct closure *);
extern struct dentry *bcache_debug;
struct closure_waitlist {
struct llist_head list;
};
enum closure_state {
/*
* 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.
*
* 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_BITS_START = (1U << 26),
CLOSURE_DESTRUCTOR = (1U << 26),
CLOSURE_WAITING = (1U << 28),
CLOSURE_RUNNING = (1U << 30),
};
#define CLOSURE_GUARD_MASK \
((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_RUNNING) << 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 closure_syncer *s;
struct llist_node list;
closure_fn *fn;
};
struct work_struct work;
};
struct closure *parent;
atomic_t remaining;
#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
#define CLOSURE_MAGIC_DEAD 0xc054dead
#define CLOSURE_MAGIC_ALIVE 0xc054a11e
unsigned int magic;
struct list_head all;
unsigned long ip;
unsigned long waiting_on;
#endif
};
void closure_sub(struct closure *cl, int v);
void closure_put(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);
/**
* closure_sync - sleep until a closure a closure has nothing left to wait on
*
* Sleeps until the refcount hits 1 - the thread that's running the closure owns
* the last refcount.
*/
static inline void closure_sync(struct closure *cl)
{
if ((atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK) != 1)
__closure_sync(cl);
}
#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_set_waiting(struct closure *cl, unsigned long f)
{
#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
cl->waiting_on = f;
#endif
}
static inline void closure_set_stopped(struct closure *cl)
{
atomic_sub(CLOSURE_RUNNING, &cl->remaining);
}
static inline void set_closure_fn(struct closure *cl, closure_fn *fn,
struct workqueue_struct *wq)
{
closure_set_ip(cl);
cl->fn = fn;
cl->wq = wq;
/* between atomic_dec() in closure_put() */
smp_mb__before_atomic();
}
static inline void closure_queue(struct closure *cl)
{
struct workqueue_struct *wq = cl->wq;
/**
* Changes made to closure, work_struct, or a couple of other structs
* may cause work.func not pointing to the right location.
*/
BUILD_BUG_ON(offsetof(struct closure, fn)
!= offsetof(struct work_struct, func));
if (wq) {
INIT_WORK(&cl->work, cl->work.func);
BUG_ON(!queue_work(wq, &cl->work));
} else
cl->fn(cl);
}
/**
* closure_get - increment a closure's refcount
*/
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
}
/**
* 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.
*/
static inline void closure_init(struct closure *cl, struct closure *parent)
{
memset(cl, 0, sizeof(struct closure));
cl->parent = parent;
if (parent)
closure_get(parent);
atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
closure_debug_create(cl);
closure_set_ip(cl);
}
static inline void closure_init_stack(struct closure *cl)
{
memset(cl, 0, sizeof(struct closure));
atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
}
/**
* closure_wake_up - wake up all closures on a wait list,
* with memory barrier
*/
static inline void closure_wake_up(struct closure_waitlist *list)
{
/* Memory barrier for the wait list */
smp_mb();
__closure_wake_up(list);
}
/**
* continue_at - jump to another function with barrier
*
* After @cl is no longer waiting on anything (i.e. all outstanding refs have
* been dropped with closure_put()), it will resume execution at @fn running out
* of @wq (or, if @wq is NULL, @fn will be called by closure_put() directly).
*
* This is because after calling continue_at() you no longer have a ref on @cl,
* and whatever @cl owns may be freed out from under you - a running closure fn
* has a ref on its own closure which continue_at() drops.
*
* Note you are expected to immediately return after using this macro.
*/
#define continue_at(_cl, _fn, _wq) \
do { \
set_closure_fn(_cl, _fn, _wq); \
closure_sub(_cl, CLOSURE_RUNNING + 1); \
} while (0)
/**
* closure_return - finish execution of a closure
*
* This is used to indicate that @cl is finished: when all outstanding refs on
* @cl have been dropped @cl's ref on its parent closure (as passed to
* closure_init()) will be dropped, if one was specified - thus this can be
* thought of as returning to the parent closure.
*/
#define closure_return(_cl) continue_at((_cl), NULL, NULL)
/**
* continue_at_nobarrier - jump to another function without barrier
*
* Causes @fn to be executed out of @cl, in @wq context (or called directly if
* @wq is NULL).
*
* The ref the caller of continue_at_nobarrier() had on @cl is now owned by @fn,
* thus it's not safe to touch anything protected by @cl after a
* continue_at_nobarrier().
*/
#define continue_at_nobarrier(_cl, _fn, _wq) \
do { \
set_closure_fn(_cl, _fn, _wq); \
closure_queue(_cl); \
} while (0)
/**
* closure_return_with_destructor - finish execution of a closure,
* with destructor
*
* Works like closure_return(), except @destructor will be called when all
* outstanding refs on @cl have been dropped; @destructor may be used to safely
* free the memory occupied by @cl, and it is called with the ref on the parent
* closure still held - so @destructor could safely return an item to a
* freelist protected by @cl's parent.
*/
#define closure_return_with_destructor(_cl, _destructor) \
do { \
set_closure_fn(_cl, _destructor, NULL); \
closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1); \
} while (0)
/**
* closure_call - execute @fn out of a new, uninitialized closure
*
* Typically used when running out of one closure, and we want to run @fn
* asynchronously out of a new closure - @parent will then wait for @cl to
* finish.
*/
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);
}
#endif /* _LINUX_CLOSURE_H */
