/* 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; closure_fn; extern struct dentry *bcache_debug; struct closure_waitlist { … }; enum closure_state { … }; #define CLOSURE_GUARD_MASK … #define CLOSURE_REMAINING_MASK … #define CLOSURE_REMAINING_INITIALIZER … struct closure { … }; 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); static inline unsigned closure_nr_remaining(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) { … } int __closure_sync_timeout(struct closure *cl, unsigned long timeout); static inline int closure_sync_timeout(struct closure *cl, unsigned long timeout) { … } #ifdef CONFIG_DEBUG_CLOSURES void closure_debug_create(struct closure *cl); void closure_debug_destroy(struct closure *cl); #else 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) { … } static inline void closure_set_ret_ip(struct closure *cl) { … } static inline void closure_set_waiting(struct closure *cl, unsigned long f) { … } static inline void closure_set_stopped(struct closure *cl) { … } static inline void set_closure_fn(struct closure *cl, closure_fn *fn, struct workqueue_struct *wq) { … } static inline void closure_queue(struct closure *cl) { … } /** * closure_get - increment a closure's refcount */ static inline void closure_get(struct closure *cl) { … } /** * closure_get_not_zero */ static inline bool closure_get_not_zero(struct closure *cl) { … } /** * 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) { … } static inline void closure_init_stack(struct closure *cl) { … } static inline void closure_init_stack_release(struct closure *cl) { … } /** * closure_wake_up - wake up all closures on a wait list, * with memory barrier */ static inline void closure_wake_up(struct closure_waitlist *list) { … } #define CLOSURE_CALLBACK(name) … #define closure_type(name, type, member) … /** * 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) … /** * 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) … void closure_return_sync(struct closure *cl); /** * 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) … /** * 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) … /** * 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) { … } #define __closure_wait_event(waitlist, _cond) … #define closure_wait_event(waitlist, _cond) … #endif /* _LINUX_CLOSURE_H */
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