cregit-Linux how code gets into the kernel

Release 4.7 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)
 * {
 *      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;

typedef void (closure_fn) (struct closure *);


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.
         *
         * 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.
         *
         * 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 << 23),
	
CLOSURE_DESTRUCTOR	= (1 << 23),
	
CLOSURE_WAITING		= (1 << 25),
	
CLOSURE_SLEEPING	= (1 << 27),
	
CLOSURE_RUNNING		= (1 << 29),
	
CLOSURE_STACK		= (1 << 31),
};


#define CLOSURE_GUARD_MASK					\
	((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_SLEEPING|  \
          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;

#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
};

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);

#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) {}

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

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

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

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

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static inline void closure_set_waiting(struct closure *cl, unsigned long f) { #ifdef CONFIG_BCACHE_CLOSURES_DEBUG cl->waiting_on = f; #endif }

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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); }

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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); }

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

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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(); }

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static inline void closure_queue(struct closure *cl) { struct workqueue_struct *wq = cl->wq; if (wq) { INIT_WORK(&cl->work, cl->work.func); BUG_ON(!queue_work(wq, &cl->work)); } else cl->fn(cl); }

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/** * 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 }

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/** * 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); }

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

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/** * 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); }

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/** * 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). * * NOTE: This macro expands to a return in the calling function! * * 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. */ #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). * * NOTE: like continue_at(), this macro expands to a return in the caller! * * 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 - 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); }

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#endif /* _LINUX_CLOSURE_H */

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