1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_CLOSURE_H
3 #define _LINUX_CLOSURE_H
5 #include <linux/llist.h>
6 #include <linux/sched.h>
7 #include <linux/sched/task_stack.h>
8 #include <linux/workqueue.h>
11 * Closure is perhaps the most overused and abused term in computer science, but
12 * since I've been unable to come up with anything better you're stuck with it
17 * They embed a refcount. The basic idea is they count "things that are in
18 * progress" - in flight bios, some other thread that's doing something else -
19 * anything you might want to wait on.
21 * The refcount may be manipulated with closure_get() and closure_put().
22 * closure_put() is where many of the interesting things happen, when it causes
23 * the refcount to go to 0.
25 * Closures can be used to wait on things both synchronously and asynchronously,
26 * and synchronous and asynchronous use can be mixed without restriction. To
27 * wait synchronously, use closure_sync() - you will sleep until your closure's
30 * To wait asynchronously, use
31 * continue_at(cl, next_function, workqueue);
33 * passing it, as you might expect, the function to run when nothing is pending
34 * and the workqueue to run that function out of.
36 * continue_at() also, critically, requires a 'return' immediately following the
37 * location where this macro is referenced, to return to the calling function.
38 * There's good reason for this.
40 * To use safely closures asynchronously, they must always have a refcount while
41 * they are running owned by the thread that is running them. Otherwise, suppose
42 * you submit some bios and wish to have a function run when they all complete:
44 * foo_endio(struct bio *bio)
53 * bio1->bi_endio = foo_endio;
58 * bio2->bi_endio = foo_endio;
61 * continue_at(cl, complete_some_read, system_wq);
63 * If closure's refcount started at 0, complete_some_read() could run before the
64 * second bio was submitted - which is almost always not what you want! More
65 * importantly, it wouldn't be possible to say whether the original thread or
66 * complete_some_read()'s thread owned the closure - and whatever state it was
69 * So, closure_init() initializes a closure's refcount to 1 - and when a
70 * closure_fn is run, the refcount will be reset to 1 first.
72 * Then, the rule is - if you got the refcount with closure_get(), release it
73 * with closure_put() (i.e, in a bio->bi_endio function). If you have a refcount
74 * on a closure because you called closure_init() or you were run out of a
75 * closure - _always_ use continue_at(). Doing so consistently will help
76 * eliminate an entire class of particularly pernicious races.
78 * Lastly, you might have a wait list dedicated to a specific event, and have no
79 * need for specifying the condition - you just want to wait until someone runs
80 * closure_wake_up() on the appropriate wait list. In that case, just use
81 * closure_wait(). It will return either true or false, depending on whether the
82 * closure was already on a wait list or not - a closure can only be on one wait
87 * closure_init() takes two arguments - it takes the closure to initialize, and
88 * a (possibly null) parent.
90 * If parent is non null, the new closure will have a refcount for its lifetime;
91 * a closure is considered to be "finished" when its refcount hits 0 and the
92 * function to run is null. Hence
94 * continue_at(cl, NULL, NULL);
96 * returns up the (spaghetti) stack of closures, precisely like normal return
97 * returns up the C stack. continue_at() with non null fn is better thought of
98 * as doing a tail call.
100 * All this implies that a closure should typically be embedded in a particular
101 * struct (which its refcount will normally control the lifetime of), and that
102 * struct can very much be thought of as a stack frame.
106 struct closure_syncer;
107 typedef void (closure_fn) (struct work_struct *);
108 extern struct dentry *bcache_debug;
110 struct closure_waitlist {
111 struct llist_head list;
116 * CLOSURE_WAITING: Set iff the closure is on a waitlist. Must be set by
117 * the thread that owns the closure, and cleared by the thread that's
118 * waking up the closure.
120 * The rest are for debugging and don't affect behaviour:
122 * CLOSURE_RUNNING: Set when a closure is running (i.e. by
123 * closure_init() and when closure_put() runs then next function), and
124 * must be cleared before remaining hits 0. Primarily to help guard
125 * against incorrect usage and accidentally transferring references.
126 * continue_at() and closure_return() clear it for you, if you're doing
127 * something unusual you can use closure_set_dead() which also helps
128 * annotate where references are being transferred.
131 CLOSURE_BITS_START = (1U << 26),
132 CLOSURE_DESTRUCTOR = (1U << 26),
133 CLOSURE_WAITING = (1U << 28),
134 CLOSURE_RUNNING = (1U << 30),
137 #define CLOSURE_GUARD_MASK \
138 ((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_RUNNING) << 1)
140 #define CLOSURE_REMAINING_MASK (CLOSURE_BITS_START - 1)
141 #define CLOSURE_REMAINING_INITIALIZER (1|CLOSURE_RUNNING)
146 struct workqueue_struct *wq;
147 struct closure_syncer *s;
148 struct llist_node list;
151 struct work_struct work;
154 struct closure *parent;
157 bool closure_get_happened;
159 #ifdef CONFIG_DEBUG_CLOSURES
160 #define CLOSURE_MAGIC_DEAD 0xc054dead
161 #define CLOSURE_MAGIC_ALIVE 0xc054a11e
164 struct list_head all;
166 unsigned long waiting_on;
170 void closure_sub(struct closure *cl, int v);
171 void closure_put(struct closure *cl);
172 void __closure_wake_up(struct closure_waitlist *list);
173 bool closure_wait(struct closure_waitlist *list, struct closure *cl);
174 void __closure_sync(struct closure *cl);
176 static inline unsigned closure_nr_remaining(struct closure *cl)
178 return atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK;
182 * closure_sync - sleep until a closure a closure has nothing left to wait on
184 * Sleeps until the refcount hits 1 - the thread that's running the closure owns
187 static inline void closure_sync(struct closure *cl)
189 #ifdef CONFIG_DEBUG_CLOSURES
190 BUG_ON(closure_nr_remaining(cl) != 1 && !cl->closure_get_happened);
193 if (cl->closure_get_happened)
197 #ifdef CONFIG_DEBUG_CLOSURES
199 void closure_debug_create(struct closure *cl);
200 void closure_debug_destroy(struct closure *cl);
204 static inline void closure_debug_create(struct closure *cl) {}
205 static inline void closure_debug_destroy(struct closure *cl) {}
209 static inline void closure_set_ip(struct closure *cl)
211 #ifdef CONFIG_DEBUG_CLOSURES
216 static inline void closure_set_ret_ip(struct closure *cl)
218 #ifdef CONFIG_DEBUG_CLOSURES
223 static inline void closure_set_waiting(struct closure *cl, unsigned long f)
225 #ifdef CONFIG_DEBUG_CLOSURES
230 static inline void closure_set_stopped(struct closure *cl)
232 atomic_sub(CLOSURE_RUNNING, &cl->remaining);
235 static inline void set_closure_fn(struct closure *cl, closure_fn *fn,
236 struct workqueue_struct *wq)
243 static inline void closure_queue(struct closure *cl)
245 struct workqueue_struct *wq = cl->wq;
247 * Changes made to closure, work_struct, or a couple of other structs
248 * may cause work.func not pointing to the right location.
250 BUILD_BUG_ON(offsetof(struct closure, fn)
251 != offsetof(struct work_struct, func));
254 INIT_WORK(&cl->work, cl->work.func);
255 BUG_ON(!queue_work(wq, &cl->work));
261 * closure_get - increment a closure's refcount
263 static inline void closure_get(struct closure *cl)
265 cl->closure_get_happened = true;
267 #ifdef CONFIG_DEBUG_CLOSURES
268 BUG_ON((atomic_inc_return(&cl->remaining) &
269 CLOSURE_REMAINING_MASK) <= 1);
271 atomic_inc(&cl->remaining);
276 * closure_init - Initialize a closure, setting the refcount to 1
277 * @cl: closure to initialize
278 * @parent: parent of the new closure. cl will take a refcount on it for its
279 * lifetime; may be NULL.
281 static inline void closure_init(struct closure *cl, struct closure *parent)
288 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
289 cl->closure_get_happened = false;
291 closure_debug_create(cl);
295 static inline void closure_init_stack(struct closure *cl)
297 memset(cl, 0, sizeof(struct closure));
298 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
302 * closure_wake_up - wake up all closures on a wait list,
303 * with memory barrier
305 static inline void closure_wake_up(struct closure_waitlist *list)
307 /* Memory barrier for the wait list */
309 __closure_wake_up(list);
312 #define CLOSURE_CALLBACK(name) void name(struct work_struct *ws)
313 #define closure_type(name, type, member) \
314 struct closure *cl = container_of(ws, struct closure, work); \
315 type *name = container_of(cl, type, member)
318 * continue_at - jump to another function with barrier
320 * After @cl is no longer waiting on anything (i.e. all outstanding refs have
321 * been dropped with closure_put()), it will resume execution at @fn running out
322 * of @wq (or, if @wq is NULL, @fn will be called by closure_put() directly).
324 * This is because after calling continue_at() you no longer have a ref on @cl,
325 * and whatever @cl owns may be freed out from under you - a running closure fn
326 * has a ref on its own closure which continue_at() drops.
328 * Note you are expected to immediately return after using this macro.
330 #define continue_at(_cl, _fn, _wq) \
332 set_closure_fn(_cl, _fn, _wq); \
333 closure_sub(_cl, CLOSURE_RUNNING + 1); \
337 * closure_return - finish execution of a closure
339 * This is used to indicate that @cl is finished: when all outstanding refs on
340 * @cl have been dropped @cl's ref on its parent closure (as passed to
341 * closure_init()) will be dropped, if one was specified - thus this can be
342 * thought of as returning to the parent closure.
344 #define closure_return(_cl) continue_at((_cl), NULL, NULL)
347 * continue_at_nobarrier - jump to another function without barrier
349 * Causes @fn to be executed out of @cl, in @wq context (or called directly if
352 * The ref the caller of continue_at_nobarrier() had on @cl is now owned by @fn,
353 * thus it's not safe to touch anything protected by @cl after a
354 * continue_at_nobarrier().
356 #define continue_at_nobarrier(_cl, _fn, _wq) \
358 set_closure_fn(_cl, _fn, _wq); \
359 closure_queue(_cl); \
363 * closure_return_with_destructor - finish execution of a closure,
366 * Works like closure_return(), except @destructor will be called when all
367 * outstanding refs on @cl have been dropped; @destructor may be used to safely
368 * free the memory occupied by @cl, and it is called with the ref on the parent
369 * closure still held - so @destructor could safely return an item to a
370 * freelist protected by @cl's parent.
372 #define closure_return_with_destructor(_cl, _destructor) \
374 set_closure_fn(_cl, _destructor, NULL); \
375 closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1); \
379 * closure_call - execute @fn out of a new, uninitialized closure
381 * Typically used when running out of one closure, and we want to run @fn
382 * asynchronously out of a new closure - @parent will then wait for @cl to
385 static inline void closure_call(struct closure *cl, closure_fn fn,
386 struct workqueue_struct *wq,
387 struct closure *parent)
389 closure_init(cl, parent);
390 continue_at_nobarrier(cl, fn, wq);
393 #define __closure_wait_event(waitlist, _cond) \
397 closure_init_stack(&cl); \
400 closure_wait(waitlist, &cl); \
405 closure_wake_up(waitlist); \
409 #define closure_wait_event(waitlist, _cond) \
412 __closure_wait_event(waitlist, _cond); \
415 #endif /* _LINUX_CLOSURE_H */