/* 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; typedef void (closure_fn) (struct work_struct *); extern struct dentry *bcache_debug; 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. * * 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_BITS_START = (1U << 26), CLOSURE_DESTRUCTOR = (1U << 26), CLOSURE_WAITING = (1U << 28), CLOSURE_RUNNING = (1U << 30), }; #define CLOSURE_GUARD_MASK \ ((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_RUNNING) << 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 closure_syncer *s; struct llist_node list; closure_fn *fn; }; struct work_struct work; }; struct closure *parent; atomic_t remaining; bool closure_get_happened; #ifdef CONFIG_DEBUG_CLOSURES #define CLOSURE_MAGIC_DEAD 0xc054dead #define CLOSURE_MAGIC_ALIVE 0xc054a11e #define CLOSURE_MAGIC_STACK 0xc05451cc unsigned int 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); static inline unsigned closure_nr_remaining(struct closure *cl) { return atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK; } /** * 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) { #ifdef CONFIG_DEBUG_CLOSURES BUG_ON(closure_nr_remaining(cl) != 1 && !cl->closure_get_happened); #endif if (cl->closure_get_happened) __closure_sync(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 BUG_ON(closure_nr_remaining(cl) != 1 && !cl->closure_get_happened); #endif return cl->closure_get_happened ? __closure_sync_timeout(cl, timeout) : 0; } #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) { #ifdef CONFIG_DEBUG_CLOSURES cl->ip = _THIS_IP_; #endif } static inline void closure_set_ret_ip(struct closure *cl) { #ifdef CONFIG_DEBUG_CLOSURES cl->ip = _RET_IP_; #endif } static inline void closure_set_waiting(struct closure *cl, unsigned long f) { #ifdef CONFIG_DEBUG_CLOSURES cl->waiting_on = f; #endif } static inline void closure_set_stopped(struct closure *cl) { atomic_sub(CLOSURE_RUNNING, &cl->remaining); } static inline void set_closure_fn(struct closure *cl, closure_fn *fn, struct workqueue_struct *wq) { closure_set_ip(cl); cl->fn = fn; cl->wq = wq; } static inline void closure_queue(struct closure *cl) { struct workqueue_struct *wq = cl->wq; /** * Changes made to closure, work_struct, or a couple of other structs * may cause work.func not pointing to the right location. */ BUILD_BUG_ON(offsetof(struct closure, fn) != offsetof(struct work_struct, func)); if (wq) { INIT_WORK(&cl->work, cl->work.func); BUG_ON(!queue_work(wq, &cl->work)); } else cl->fn(&cl->work); } /** * closure_get - increment a closure's refcount */ static inline void closure_get(struct closure *cl) { cl->closure_get_happened = true; #ifdef CONFIG_DEBUG_CLOSURES BUG_ON((atomic_inc_return(&cl->remaining) & CLOSURE_REMAINING_MASK) <= 1); #else atomic_inc(&cl->remaining); #endif } /** * closure_get_not_zero */ static inline bool closure_get_not_zero(struct closure *cl) { unsigned old = atomic_read(&cl->remaining); do { if (!(old & CLOSURE_REMAINING_MASK)) return false; } while (!atomic_try_cmpxchg_acquire(&cl->remaining, &old, old + 1)); return true; } /** * 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) { cl->fn = NULL; cl->parent = parent; if (parent) closure_get(parent); atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); cl->closure_get_happened = false; closure_debug_create(cl); closure_set_ip(cl); } static inline void closure_init_stack(struct closure *cl) { memset(cl, 0, sizeof(struct closure)); atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); #ifdef CONFIG_DEBUG_CLOSURES cl->magic = CLOSURE_MAGIC_STACK; #endif } static inline void closure_init_stack_release(struct closure *cl) { memset(cl, 0, sizeof(struct closure)); atomic_set_release(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); #ifdef CONFIG_DEBUG_CLOSURES cl->magic = CLOSURE_MAGIC_STACK; #endif } /** * closure_wake_up - wake up all closures on a wait list, * with memory barrier */ static inline void closure_wake_up(struct closure_waitlist *list) { /* Memory barrier for the wait list */ smp_mb(); __closure_wake_up(list); } #define CLOSURE_CALLBACK(name) void name(struct work_struct *ws) #define closure_type(name, type, member) \ struct closure *cl = container_of(ws, struct closure, work); \ type *name = container_of(cl, 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) \ 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) 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) \ do { \ set_closure_fn(_cl, _fn, _wq); \ closure_queue(_cl); \ } while (0) /** * 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) \ 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); } #define __closure_wait_event(waitlist, _cond) \ do { \ struct closure cl; \ \ closure_init_stack(&cl); \ \ while (1) { \ closure_wait(waitlist, &cl); \ if (_cond) \ break; \ closure_sync(&cl); \ } \ closure_wake_up(waitlist); \ closure_sync(&cl); \ } while (0) #define closure_wait_event(waitlist, _cond) \ do { \ if (!(_cond)) \ __closure_wait_event(waitlist, _cond); \ } while (0) #define __closure_wait_event_timeout(waitlist, _cond, _until) \ ({ \ struct closure cl; \ long _t; \ \ closure_init_stack(&cl); \ \ while (1) { \ closure_wait(waitlist, &cl); \ if (_cond) { \ _t = max_t(long, 1L, _until - jiffies); \ break; \ } \ _t = max_t(long, 0L, _until - jiffies); \ if (!_t) \ break; \ closure_sync_timeout(&cl, _t); \ } \ closure_wake_up(waitlist); \ closure_sync(&cl); \ _t; \ }) /* * Returns 0 if timeout expired, remaining time in jiffies (at least 1) if * condition became true */ #define closure_wait_event_timeout(waitlist, _cond, _timeout) \ ({ \ unsigned long _until = jiffies + _timeout; \ (_cond) \ ? max_t(long, 1L, _until - jiffies) \ : __closure_wait_event_timeout(waitlist, _cond, _until);\ }) #endif /* _LINUX_CLOSURE_H */
