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/rcupdate.h>
7 #include <linux/sched.h>
8 #include <linux/sched/task_stack.h>
9 #include <linux/workqueue.h>
12 * Closure is perhaps the most overused and abused term in computer science, but
13 * since I've been unable to come up with anything better you're stuck with it
18 * They embed a refcount. The basic idea is they count "things that are in
19 * progress" - in flight bios, some other thread that's doing something else -
20 * anything you might want to wait on.
22 * The refcount may be manipulated with closure_get() and closure_put().
23 * closure_put() is where many of the interesting things happen, when it causes
24 * the refcount to go to 0.
26 * Closures can be used to wait on things both synchronously and asynchronously,
27 * and synchronous and asynchronous use can be mixed without restriction. To
28 * wait synchronously, use closure_sync() - you will sleep until your closure's
31 * To wait asynchronously, use
32 * continue_at(cl, next_function, workqueue);
34 * passing it, as you might expect, the function to run when nothing is pending
35 * and the workqueue to run that function out of.
37 * continue_at() also, critically, requires a 'return' immediately following the
38 * location where this macro is referenced, to return to the calling function.
39 * There's good reason for this.
41 * To use safely closures asynchronously, they must always have a refcount while
42 * they are running owned by the thread that is running them. Otherwise, suppose
43 * you submit some bios and wish to have a function run when they all complete:
45 * foo_endio(struct bio *bio)
54 * bio1->bi_endio = foo_endio;
59 * bio2->bi_endio = foo_endio;
62 * continue_at(cl, complete_some_read, system_wq);
64 * If closure's refcount started at 0, complete_some_read() could run before the
65 * second bio was submitted - which is almost always not what you want! More
66 * importantly, it wouldn't be possible to say whether the original thread or
67 * complete_some_read()'s thread owned the closure - and whatever state it was
70 * So, closure_init() initializes a closure's refcount to 1 - and when a
71 * closure_fn is run, the refcount will be reset to 1 first.
73 * Then, the rule is - if you got the refcount with closure_get(), release it
74 * with closure_put() (i.e, in a bio->bi_endio function). If you have a refcount
75 * on a closure because you called closure_init() or you were run out of a
76 * closure - _always_ use continue_at(). Doing so consistently will help
77 * eliminate an entire class of particularly pernicious races.
79 * Lastly, you might have a wait list dedicated to a specific event, and have no
80 * need for specifying the condition - you just want to wait until someone runs
81 * closure_wake_up() on the appropriate wait list. In that case, just use
82 * closure_wait(). It will return either true or false, depending on whether the
83 * closure was already on a wait list or not - a closure can only be on one wait
88 * closure_init() takes two arguments - it takes the closure to initialize, and
89 * a (possibly null) parent.
91 * If parent is non null, the new closure will have a refcount for its lifetime;
92 * a closure is considered to be "finished" when its refcount hits 0 and the
93 * function to run is null. Hence
95 * continue_at(cl, NULL, NULL);
97 * returns up the (spaghetti) stack of closures, precisely like normal return
98 * returns up the C stack. continue_at() with non null fn is better thought of
99 * as doing a tail call.
101 * All this implies that a closure should typically be embedded in a particular
102 * struct (which its refcount will normally control the lifetime of), and that
103 * struct can very much be thought of as a stack frame.
107 struct closure_syncer;
108 typedef void (closure_fn) (struct closure *);
109 extern struct dentry *bcache_debug;
111 struct closure_waitlist {
112 struct llist_head list;
117 * CLOSURE_WAITING: Set iff the closure is on a waitlist. Must be set by
118 * the thread that owns the closure, and cleared by the thread that's
119 * waking up the closure.
121 * The rest are for debugging and don't affect behaviour:
123 * CLOSURE_RUNNING: Set when a closure is running (i.e. by
124 * closure_init() and when closure_put() runs then next function), and
125 * must be cleared before remaining hits 0. Primarily to help guard
126 * against incorrect usage and accidentally transferring references.
127 * continue_at() and closure_return() clear it for you, if you're doing
128 * something unusual you can use closure_set_dead() which also helps
129 * annotate where references are being transferred.
132 CLOSURE_BITS_START = (1U << 26),
133 CLOSURE_DESTRUCTOR = (1U << 26),
134 CLOSURE_WAITING = (1U << 28),
135 CLOSURE_RUNNING = (1U << 30),
138 #define CLOSURE_GUARD_MASK \
139 ((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_RUNNING) << 1)
141 #define CLOSURE_REMAINING_MASK (CLOSURE_BITS_START - 1)
142 #define CLOSURE_REMAINING_INITIALIZER (1|CLOSURE_RUNNING)
147 struct workqueue_struct *wq;
148 struct closure_syncer *s;
149 struct llist_node list;
152 struct work_struct work;
155 struct closure *parent;
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);
177 * closure_sync - sleep until a closure a closure has nothing left to wait on
179 * Sleeps until the refcount hits 1 - the thread that's running the closure owns
182 static inline void closure_sync(struct closure *cl)
184 if ((atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK) != 1)
188 #ifdef CONFIG_DEBUG_CLOSURES
190 void closure_debug_create(struct closure *cl);
191 void closure_debug_destroy(struct closure *cl);
195 static inline void closure_debug_create(struct closure *cl) {}
196 static inline void closure_debug_destroy(struct closure *cl) {}
200 static inline void closure_set_ip(struct closure *cl)
202 #ifdef CONFIG_DEBUG_CLOSURES
207 static inline void closure_set_ret_ip(struct closure *cl)
209 #ifdef CONFIG_DEBUG_CLOSURES
214 static inline void closure_set_waiting(struct closure *cl, unsigned long f)
216 #ifdef CONFIG_DEBUG_CLOSURES
221 static inline void closure_set_stopped(struct closure *cl)
223 atomic_sub(CLOSURE_RUNNING, &cl->remaining);
226 static inline void set_closure_fn(struct closure *cl, closure_fn *fn,
227 struct workqueue_struct *wq)
232 /* between atomic_dec() in closure_put() */
233 smp_mb__before_atomic();
236 static inline void closure_queue(struct closure *cl)
238 struct workqueue_struct *wq = cl->wq;
240 * Changes made to closure, work_struct, or a couple of other structs
241 * may cause work.func not pointing to the right location.
243 BUILD_BUG_ON(offsetof(struct closure, fn)
244 != offsetof(struct work_struct, func));
247 INIT_WORK(&cl->work, cl->work.func);
248 BUG_ON(!queue_work(wq, &cl->work));
254 * closure_get - increment a closure's refcount
256 static inline void closure_get(struct closure *cl)
258 #ifdef CONFIG_DEBUG_CLOSURES
259 BUG_ON((atomic_inc_return(&cl->remaining) &
260 CLOSURE_REMAINING_MASK) <= 1);
262 atomic_inc(&cl->remaining);
267 * closure_init - Initialize a closure, setting the refcount to 1
268 * @cl: closure to initialize
269 * @parent: parent of the new closure. cl will take a refcount on it for its
270 * lifetime; may be NULL.
272 static inline void closure_init(struct closure *cl, struct closure *parent)
279 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
281 closure_debug_create(cl);
285 static inline void closure_init_stack(struct closure *cl)
287 memset(cl, 0, sizeof(struct closure));
288 atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
292 * closure_wake_up - wake up all closures on a wait list,
293 * with memory barrier
295 static inline void closure_wake_up(struct closure_waitlist *list)
297 /* Memory barrier for the wait list */
299 __closure_wake_up(list);
303 * continue_at - jump to another function with barrier
305 * After @cl is no longer waiting on anything (i.e. all outstanding refs have
306 * been dropped with closure_put()), it will resume execution at @fn running out
307 * of @wq (or, if @wq is NULL, @fn will be called by closure_put() directly).
309 * This is because after calling continue_at() you no longer have a ref on @cl,
310 * and whatever @cl owns may be freed out from under you - a running closure fn
311 * has a ref on its own closure which continue_at() drops.
313 * Note you are expected to immediately return after using this macro.
315 #define continue_at(_cl, _fn, _wq) \
317 set_closure_fn(_cl, _fn, _wq); \
318 closure_sub(_cl, CLOSURE_RUNNING + 1); \
322 * closure_return - finish execution of a closure
324 * This is used to indicate that @cl is finished: when all outstanding refs on
325 * @cl have been dropped @cl's ref on its parent closure (as passed to
326 * closure_init()) will be dropped, if one was specified - thus this can be
327 * thought of as returning to the parent closure.
329 #define closure_return(_cl) continue_at((_cl), NULL, NULL)
332 * continue_at_nobarrier - jump to another function without barrier
334 * Causes @fn to be executed out of @cl, in @wq context (or called directly if
337 * The ref the caller of continue_at_nobarrier() had on @cl is now owned by @fn,
338 * thus it's not safe to touch anything protected by @cl after a
339 * continue_at_nobarrier().
341 #define continue_at_nobarrier(_cl, _fn, _wq) \
343 set_closure_fn(_cl, _fn, _wq); \
344 closure_queue(_cl); \
348 * closure_return_with_destructor - finish execution of a closure,
351 * Works like closure_return(), except @destructor will be called when all
352 * outstanding refs on @cl have been dropped; @destructor may be used to safely
353 * free the memory occupied by @cl, and it is called with the ref on the parent
354 * closure still held - so @destructor could safely return an item to a
355 * freelist protected by @cl's parent.
357 #define closure_return_with_destructor(_cl, _destructor) \
359 set_closure_fn(_cl, _destructor, NULL); \
360 closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1); \
364 * closure_call - execute @fn out of a new, uninitialized closure
366 * Typically used when running out of one closure, and we want to run @fn
367 * asynchronously out of a new closure - @parent will then wait for @cl to
370 static inline void closure_call(struct closure *cl, closure_fn fn,
371 struct workqueue_struct *wq,
372 struct closure *parent)
374 closure_init(cl, parent);
375 continue_at_nobarrier(cl, fn, wq);
378 #define __closure_wait_event(waitlist, _cond) \
382 closure_init_stack(&cl); \
385 closure_wait(waitlist, &cl); \
390 closure_wake_up(waitlist); \
394 #define closure_wait_event(waitlist, _cond) \
397 __closure_wait_event(waitlist, _cond); \
400 #endif /* _LINUX_CLOSURE_H */