1 #ifndef _LINUX_CLOSURE_H
2 #define _LINUX_CLOSURE_H
4 #include <linux/llist.h>
5 #include <linux/sched.h>
6 #include <linux/workqueue.h>
9 * Closure is perhaps the most overused and abused term in computer science, but
10 * since I've been unable to come up with anything better you're stuck with it
15 * They embed a refcount. The basic idea is they count "things that are in
16 * progress" - in flight bios, some other thread that's doing something else -
17 * anything you might want to wait on.
19 * The refcount may be manipulated with closure_get() and closure_put().
20 * closure_put() is where many of the interesting things happen, when it causes
21 * the refcount to go to 0.
23 * Closures can be used to wait on things both synchronously and asynchronously,
24 * and synchronous and asynchronous use can be mixed without restriction. To
25 * wait synchronously, use closure_sync() - you will sleep until your closure's
28 * To wait asynchronously, use
29 * continue_at(cl, next_function, workqueue);
31 * passing it, as you might expect, the function to run when nothing is pending
32 * and the workqueue to run that function out of.
34 * continue_at() also, critically, requires a 'return' immediately following the
35 * location where this macro is referenced, to return to the calling function.
36 * There's good reason for this.
38 * To use safely closures asynchronously, they must always have a refcount while
39 * they are running owned by the thread that is running them. Otherwise, suppose
40 * you submit some bios and wish to have a function run when they all complete:
42 * foo_endio(struct bio *bio)
51 * bio1->bi_endio = foo_endio;
56 * bio2->bi_endio = foo_endio;
59 * continue_at(cl, complete_some_read, system_wq);
61 * If closure's refcount started at 0, complete_some_read() could run before the
62 * second bio was submitted - which is almost always not what you want! More
63 * importantly, it wouldn't be possible to say whether the original thread or
64 * complete_some_read()'s thread owned the closure - and whatever state it was
67 * So, closure_init() initializes a closure's refcount to 1 - and when a
68 * closure_fn is run, the refcount will be reset to 1 first.
70 * Then, the rule is - if you got the refcount with closure_get(), release it
71 * with closure_put() (i.e, in a bio->bi_endio function). If you have a refcount
72 * on a closure because you called closure_init() or you were run out of a
73 * closure - _always_ use continue_at(). Doing so consistently will help
74 * eliminate an entire class of particularly pernicious races.
76 * Lastly, you might have a wait list dedicated to a specific event, and have no
77 * need for specifying the condition - you just want to wait until someone runs
78 * closure_wake_up() on the appropriate wait list. In that case, just use
79 * closure_wait(). It will return either true or false, depending on whether the
80 * closure was already on a wait list or not - a closure can only be on one wait
85 * closure_init() takes two arguments - it takes the closure to initialize, and
86 * a (possibly null) parent.
88 * If parent is non null, the new closure will have a refcount for its lifetime;
89 * a closure is considered to be "finished" when its refcount hits 0 and the
90 * function to run is null. Hence
92 * continue_at(cl, NULL, NULL);
94 * returns up the (spaghetti) stack of closures, precisely like normal return
95 * returns up the C stack. continue_at() with non null fn is better thought of
96 * as doing a tail call.
98 * All this implies that a closure should typically be embedded in a particular
99 * struct (which its refcount will normally control the lifetime of), and that
100 * struct can very much be thought of as a stack frame.
104 struct closure_syncer;
105 typedef void (closure_fn) (struct closure *);
107 struct closure_waitlist {
108 struct llist_head list;
113 * CLOSURE_WAITING: Set iff the closure is on a waitlist. Must be set by
114 * the thread that owns the closure, and cleared by the thread that's
115 * waking up the closure.
117 * The rest are for debugging and don't affect behaviour:
119 * CLOSURE_RUNNING: Set when a closure is running (i.e. by
120 * closure_init() and when closure_put() runs then next function), and
121 * must be cleared before remaining hits 0. Primarily to help guard
122 * against incorrect usage and accidentally transferring references.
123 * continue_at() and closure_return() clear it for you, if you're doing
124 * something unusual you can use closure_set_dead() which also helps
125 * annotate where references are being transferred.
128 CLOSURE_BITS_START = (1U << 27),
129 CLOSURE_DESTRUCTOR = (1U << 27),
130 CLOSURE_WAITING = (1U << 29),
131 CLOSURE_RUNNING = (1U << 31),
134 #define CLOSURE_GUARD_MASK \
135 ((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_RUNNING) << 1)
137 #define CLOSURE_REMAINING_MASK (CLOSURE_BITS_START - 1)
138 #define CLOSURE_REMAINING_INITIALIZER (1|CLOSURE_RUNNING)
143 struct workqueue_struct *wq;
144 struct closure_syncer *s;
145 struct llist_node list;
148 struct work_struct work;
151 struct closure *parent;
155 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG
156 #define CLOSURE_MAGIC_DEAD 0xc054dead
157 #define CLOSURE_MAGIC_ALIVE 0xc054a11e
160 struct list_head all;
162 unsigned long waiting_on;
166 void closure_sub(struct closure *cl, int v);
167 void closure_put(struct closure *cl);
168 void __closure_wake_up(struct closure_waitlist *list);
169 bool closure_wait(struct closure_waitlist *list, struct closure *cl);
170 void __closure_sync(struct closure *cl);
173 * closure_sync - sleep until a closure a closure has nothing left to wait on
175 * Sleeps until the refcount hits 1 - the thread that's running the closure owns
178 static inline void closure_sync(struct closure *cl)
180 if ((atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK) != 1)
184 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG
186 void closure_debug_init(void);
187 void closure_debug_create(struct closure *cl);
188 void closure_debug_destroy(struct closure *cl);
192 static inline void closure_debug_init(void) {}
193 static inline void closure_debug_create(struct closure *cl) {}
194 static inline void closure_debug_destroy(struct closure *cl) {}
198 static inline void closure_set_ip(struct closure *cl)
200 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG
205 static inline void closure_set_ret_ip(struct closure *cl)
207 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG
212 static inline void closure_set_waiting(struct closure *cl, unsigned long f)
214 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG
219 static inline void closure_set_stopped(struct closure *cl)
221 atomic_sub(CLOSURE_RUNNING, &cl->remaining);
224 static inline void set_closure_fn(struct closure *cl, closure_fn *fn,
225 struct workqueue_struct *wq)
230 /* between atomic_dec() in closure_put() */
231 smp_mb__before_atomic();
234 static inline void closure_queue(struct closure *cl)
236 struct workqueue_struct *wq = cl->wq;
239 INIT_WORK(&cl->work, cl->work.func);
240 queue_work(wq, &cl->work);
246 * closure_get - increment a closure's refcount
248 static inline void closure_get(struct closure *cl)
250 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG
251 BUG_ON((atomic_inc_return(&cl->remaining) &
252 CLOSURE_REMAINING_MASK) <= 1);
254 atomic_inc(&cl->remaining);
259 * closure_init - Initialize a closure, setting the refcount to 1
260 * @cl: closure to initialize
261 * @parent: parent of the new closure. cl will take a refcount on it for its
262 * lifetime; may be NULL.
264 static inline void closure_init(struct closure *cl, struct closure *parent)
271 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
273 closure_debug_create(cl);
277 static inline void closure_init_stack(struct closure *cl)
279 memset(cl, 0, sizeof(struct closure));
280 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
284 * closure_wake_up - wake up all closures on a wait list.
286 static inline void closure_wake_up(struct closure_waitlist *list)
289 __closure_wake_up(list);
292 #define continue_at_noreturn(_cl, _fn, _wq) \
294 set_closure_fn(_cl, _fn, _wq); \
295 closure_sub(_cl, CLOSURE_RUNNING + 1); \
299 * continue_at - jump to another function with barrier
301 * After @cl is no longer waiting on anything (i.e. all outstanding refs have
302 * been dropped with closure_put()), it will resume execution at @fn running out
303 * of @wq (or, if @wq is NULL, @fn will be called by closure_put() directly).
305 * NOTE: This macro expands to a return in the calling function!
307 * This is because after calling continue_at() you no longer have a ref on @cl,
308 * and whatever @cl owns may be freed out from under you - a running closure fn
309 * has a ref on its own closure which continue_at() drops.
311 #define continue_at(_cl, _fn, _wq) \
313 continue_at_noreturn(_cl, _fn, _wq); \
318 * closure_return - finish execution of a closure
320 * This is used to indicate that @cl is finished: when all outstanding refs on
321 * @cl have been dropped @cl's ref on its parent closure (as passed to
322 * closure_init()) will be dropped, if one was specified - thus this can be
323 * thought of as returning to the parent closure.
325 #define closure_return(_cl) continue_at((_cl), NULL, NULL)
328 * continue_at_nobarrier - jump to another function without barrier
330 * Causes @fn to be executed out of @cl, in @wq context (or called directly if
333 * NOTE: like continue_at(), this macro expands to a return in the caller!
335 * The ref the caller of continue_at_nobarrier() had on @cl is now owned by @fn,
336 * thus it's not safe to touch anything protected by @cl after a
337 * continue_at_nobarrier().
339 #define continue_at_nobarrier(_cl, _fn, _wq) \
341 closure_set_ip(cl); \
343 INIT_WORK(&(_cl)->work, (void *) _fn); \
344 queue_work((_wq), &(_cl)->work); \
351 #define closure_return_with_destructor_noreturn(_cl, _destructor) \
353 set_closure_fn(_cl, _destructor, NULL); \
354 closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1); \
358 * closure_return - finish execution of a closure, with destructor
360 * Works like closure_return(), except @destructor will be called when all
361 * outstanding refs on @cl have been dropped; @destructor may be used to safely
362 * free the memory occupied by @cl, and it is called with the ref on the parent
363 * closure still held - so @destructor could safely return an item to a
364 * freelist protected by @cl's parent.
366 #define closure_return_with_destructor(_cl, _destructor) \
368 closure_return_with_destructor_noreturn(_cl, _destructor); \
373 * closure_call - execute @fn out of a new, uninitialized closure
375 * Typically used when running out of one closure, and we want to run @fn
376 * asynchronously out of a new closure - @parent will then wait for @cl to
379 static inline void closure_call(struct closure *cl, closure_fn fn,
380 struct workqueue_struct *wq,
381 struct closure *parent)
383 closure_init(cl, parent);
384 continue_at_nobarrier(cl, fn, wq);
387 #endif /* _LINUX_CLOSURE_H */