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Diffstat (limited to 'drivers/md/bcache/closure.h')
| -rw-r--r-- | drivers/md/bcache/closure.h | 672 |
1 files changed, 672 insertions, 0 deletions
diff --git a/drivers/md/bcache/closure.h b/drivers/md/bcache/closure.h new file mode 100644 index 000000000000..00039924ea9d --- /dev/null +++ b/drivers/md/bcache/closure.h @@ -0,0 +1,672 @@ +#ifndef _LINUX_CLOSURE_H +#define _LINUX_CLOSURE_H + +#include <linux/llist.h> +#include <linux/sched.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, is a macro that returns 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, int error) + * { + * 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. + * + * For a closure to wait on an arbitrary event, we need to introduce waitlists: + * + * struct closure_waitlist list; + * closure_wait_event(list, cl, condition); + * closure_wake_up(wait_list); + * + * These work analagously to wait_event() and wake_up() - except that instead of + * operating on the current thread (for wait_event()) and lists of threads, they + * operate on an explicit closure and lists of closures. + * + * Because it's a closure we can now wait either synchronously or + * asynchronously. closure_wait_event() returns the current value of the + * condition, and if it returned false continue_at() or closure_sync() can be + * used to wait for it to become true. + * + * It's useful for waiting on things when you can't sleep in the context in + * which you must check the condition (perhaps a spinlock held, or you might be + * beneath generic_make_request() - in which case you can't sleep on IO). + * + * closure_wait_event() will wait either synchronously or asynchronously, + * depending on whether the closure is in blocking mode or not. You can pick a + * mode explicitly with closure_wait_event_sync() and + * closure_wait_event_async(), which do just what you might expect. + * + * 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. + * + * Locking: + * + * Closures are based on work items but they can be thought of as more like + * threads - in that like threads and unlike work items they have a well + * defined lifetime; they are created (with closure_init()) and eventually + * complete after a continue_at(cl, NULL, NULL). + * + * Suppose you've got some larger structure with a closure embedded in it that's + * used for periodically doing garbage collection. You only want one garbage + * collection happening at a time, so the natural thing to do is protect it with + * a lock. However, it's difficult to use a lock protecting a closure correctly + * because the unlock should come after the last continue_to() (additionally, if + * you're using the closure asynchronously a mutex won't work since a mutex has + * to be unlocked by the same process that locked it). + * + * So to make it less error prone and more efficient, we also have the ability + * to use closures as locks: + * + * closure_init_unlocked(); + * closure_trylock(); + * + * That's all we need for trylock() - the last closure_put() implicitly unlocks + * it for you. But for closure_lock(), we also need a wait list: + * + * struct closure_with_waitlist frobnicator_cl; + * + * closure_init_unlocked(&frobnicator_cl); + * closure_lock(&frobnicator_cl); + * + * A closure_with_waitlist embeds a closure and a wait list - much like struct + * delayed_work embeds a work item and a timer_list. The important thing is, use + * it exactly like you would a regular closure and closure_put() will magically + * handle everything for you. + * + * We've got closures that embed timers, too. They're called, appropriately + * enough: + * struct closure_with_timer; + * + * This gives you access to closure_delay(). It takes a refcount for a specified + * number of jiffies - you could then call closure_sync() (for a slightly + * convoluted version of msleep()) or continue_at() - which gives you the same + * effect as using a delayed work item, except you can reuse the work_struct + * already embedded in struct closure. + * + * Lastly, there's struct closure_with_waitlist_and_timer. It does what you + * probably expect, if you happen to need the features of both. (You don't + * really want to know how all this is implemented, but if I've done my job + * right you shouldn't have to care). + */ + +struct closure; +typedef void (closure_fn) (struct closure *); + +struct closure_waitlist { + struct llist_head list; +}; + +enum closure_type { + TYPE_closure = 0, + TYPE_closure_with_waitlist = 1, + TYPE_closure_with_timer = 2, + TYPE_closure_with_waitlist_and_timer = 3, + MAX_CLOSURE_TYPE = 3, +}; + +enum closure_state { + /* + * CLOSURE_BLOCKING: Causes closure_wait_event() to block, instead of + * waiting asynchronously + * + * 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. + * + * CLOSURE_SLEEPING: Must be set before a thread uses a closure to sleep + * - indicates that cl->task is valid and closure_put() may wake it up. + * Only set or cleared by the thread that owns the closure. + * + * CLOSURE_TIMER: Analagous to CLOSURE_WAITING, indicates that a closure + * has an outstanding timer. Must be set by the thread that owns the + * closure, and cleared by the timer function when the timer goes off. + * + * 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_STACK: Sanity check - remaining should never hit 0 on a + * closure with this flag set + */ + + CLOSURE_BITS_START = (1 << 19), + CLOSURE_DESTRUCTOR = (1 << 19), + CLOSURE_BLOCKING = (1 << 21), + CLOSURE_WAITING = (1 << 23), + CLOSURE_SLEEPING = (1 << 25), + CLOSURE_TIMER = (1 << 27), + CLOSURE_RUNNING = (1 << 29), + CLOSURE_STACK = (1 << 31), +}; + +#define CLOSURE_GUARD_MASK \ + ((CLOSURE_DESTRUCTOR|CLOSURE_BLOCKING|CLOSURE_WAITING| \ + CLOSURE_SLEEPING|CLOSURE_TIMER|CLOSURE_RUNNING|CLOSURE_STACK) << 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 task_struct *task; + struct llist_node list; + closure_fn *fn; + }; + struct work_struct work; + }; + + struct closure *parent; + + atomic_t remaining; + + enum closure_type type; + +#ifdef CONFIG_BCACHE_CLOSURES_DEBUG +#define CLOSURE_MAGIC_DEAD 0xc054dead +#define CLOSURE_MAGIC_ALIVE 0xc054a11e + + unsigned magic; + struct list_head all; + unsigned long ip; + unsigned long waiting_on; +#endif +}; + +struct closure_with_waitlist { + struct closure cl; + struct closure_waitlist wait; +}; + +struct closure_with_timer { + struct closure cl; + struct timer_list timer; +}; + +struct closure_with_waitlist_and_timer { + struct closure cl; + struct closure_waitlist wait; + struct timer_list timer; +}; + +extern unsigned invalid_closure_type(void); + +#define __CLOSURE_TYPE(cl, _t) \ + __builtin_types_compatible_p(typeof(cl), struct _t) \ + ? TYPE_ ## _t : \ + +#define __closure_type(cl) \ +( \ + __CLOSURE_TYPE(cl, closure) \ + __CLOSURE_TYPE(cl, closure_with_waitlist) \ + __CLOSURE_TYPE(cl, closure_with_timer) \ + __CLOSURE_TYPE(cl, closure_with_waitlist_and_timer) \ + invalid_closure_type() \ +) + +void closure_sub(struct closure *cl, int v); +void closure_put(struct closure *cl); +void closure_queue(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); + +bool closure_trylock(struct closure *cl, struct closure *parent); +void __closure_lock(struct closure *cl, struct closure *parent, + struct closure_waitlist *wait_list); + +void do_closure_timer_init(struct closure *cl); +bool __closure_delay(struct closure *cl, unsigned long delay, + struct timer_list *timer); +void __closure_flush(struct closure *cl, struct timer_list *timer); +void __closure_flush_sync(struct closure *cl, struct timer_list *timer); + +#ifdef CONFIG_BCACHE_CLOSURES_DEBUG + +void closure_debug_init(void); +void closure_debug_create(struct closure *cl); +void closure_debug_destroy(struct closure *cl); + +#else + +static inline void closure_debug_init(void) {} +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_BCACHE_CLOSURES_DEBUG + cl->ip = _THIS_IP_; +#endif +} + +static inline void closure_set_ret_ip(struct closure *cl) +{ +#ifdef CONFIG_BCACHE_CLOSURES_DEBUG + cl->ip = _RET_IP_; +#endif +} + +static inline void closure_get(struct closure *cl) +{ +#ifdef CONFIG_BCACHE_CLOSURES_DEBUG + BUG_ON((atomic_inc_return(&cl->remaining) & + CLOSURE_REMAINING_MASK) <= 1); +#else + atomic_inc(&cl->remaining); +#endif +} + +static inline void closure_set_stopped(struct closure *cl) +{ + atomic_sub(CLOSURE_RUNNING, &cl->remaining); +} + +static inline bool closure_is_stopped(struct closure *cl) +{ + return !(atomic_read(&cl->remaining) & CLOSURE_RUNNING); +} + +static inline bool closure_is_unlocked(struct closure *cl) +{ + return atomic_read(&cl->remaining) == -1; +} + +static inline void do_closure_init(struct closure *cl, struct closure *parent, + bool running) +{ + switch (cl->type) { + case TYPE_closure_with_timer: + case TYPE_closure_with_waitlist_and_timer: + do_closure_timer_init(cl); + default: + break; + } + + cl->parent = parent; + if (parent) + closure_get(parent); + + if (running) { + closure_debug_create(cl); + atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); + } else + atomic_set(&cl->remaining, -1); + + closure_set_ip(cl); +} + +/* + * Hack to get at the embedded closure if there is one, by doing an unsafe cast: + * the result of __closure_type() is thrown away, it's used merely for type + * checking. + */ +#define __to_internal_closure(cl) \ +({ \ + BUILD_BUG_ON(__closure_type(*cl) > MAX_CLOSURE_TYPE); \ + (struct closure *) cl; \ +}) + +#define closure_init_type(cl, parent, running) \ +do { \ + struct closure *_cl = __to_internal_closure(cl); \ + _cl->type = __closure_type(*(cl)); \ + do_closure_init(_cl, parent, running); \ +} while (0) + +/** + * __closure_init() - Initialize a closure, skipping the memset() + * + * May be used instead of closure_init() when memory has already been zeroed. + */ +#define __closure_init(cl, parent) \ + closure_init_type(cl, parent, 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. + */ +#define closure_init(cl, parent) \ +do { \ + memset((cl), 0, sizeof(*(cl))); \ + __closure_init(cl, parent); \ +} while (0) + +static inline void closure_init_stack(struct closure *cl) +{ + memset(cl, 0, sizeof(struct closure)); + atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER| + CLOSURE_BLOCKING|CLOSURE_STACK); +} + +/** + * closure_init_unlocked() - Initialize a closure but leave it unlocked. + * @cl: closure to initialize + * + * For when the closure will be used as a lock. The closure may not be used + * until after a closure_lock() or closure_trylock(). + */ +#define closure_init_unlocked(cl) \ +do { \ + memset((cl), 0, sizeof(*(cl))); \ + closure_init_type(cl, NULL, false); \ +} while (0) + +/** + * closure_lock() - lock and initialize a closure. + * @cl: the closure to lock + * @parent: the new parent for this closure + * + * The closure must be of one of the types that has a waitlist (otherwise we + * wouldn't be able to sleep on contention). + * + * @parent has exactly the same meaning as in closure_init(); if non null, the + * closure will take a reference on @parent which will be released when it is + * unlocked. + */ +#define closure_lock(cl, parent) \ + __closure_lock(__to_internal_closure(cl), parent, &(cl)->wait) + +/** + * closure_delay() - delay some number of jiffies + * @cl: the closure that will sleep + * @delay: the delay in jiffies + * + * Takes a refcount on @cl which will be released after @delay jiffies; this may + * be used to have a function run after a delay with continue_at(), or + * closure_sync() may be used for a convoluted version of msleep(). + */ +#define closure_delay(cl, delay) \ + __closure_delay(__to_internal_closure(cl), delay, &(cl)->timer) + +#define closure_flush(cl) \ + __closure_flush(__to_internal_closure(cl), &(cl)->timer) + +#define closure_flush_sync(cl) \ + __closure_flush_sync(__to_internal_closure(cl), &(cl)->timer) + +static inline void __closure_end_sleep(struct closure *cl) +{ + __set_current_state(TASK_RUNNING); + + if (atomic_read(&cl->remaining) & CLOSURE_SLEEPING) + atomic_sub(CLOSURE_SLEEPING, &cl->remaining); +} + +static inline void __closure_start_sleep(struct closure *cl) +{ + closure_set_ip(cl); + cl->task = current; + set_current_state(TASK_UNINTERRUPTIBLE); + + if (!(atomic_read(&cl->remaining) & CLOSURE_SLEEPING)) + atomic_add(CLOSURE_SLEEPING, &cl->remaining); +} + +/** + * closure_blocking() - returns true if the closure is in blocking mode. + * + * If a closure is in blocking mode, closure_wait_event() will sleep until the + * condition is true instead of waiting asynchronously. + */ +static inline bool closure_blocking(struct closure *cl) +{ + return atomic_read(&cl->remaining) & CLOSURE_BLOCKING; +} + +/** + * set_closure_blocking() - put a closure in blocking mode. + * + * If a closure is in blocking mode, closure_wait_event() will sleep until the + * condition is true instead of waiting asynchronously. + * + * Not thread safe - can only be called by the thread running the closure. + */ +static inline void set_closure_blocking(struct closure *cl) +{ + if (!closure_blocking(cl)) + atomic_add(CLOSURE_BLOCKING, &cl->remaining); +} + +/* + * Not thread safe - can only be called by the thread running the closure. + */ +static inline void clear_closure_blocking(struct closure *cl) +{ + if (closure_blocking(cl)) + atomic_sub(CLOSURE_BLOCKING, &cl->remaining); +} + +/** + * closure_wake_up() - wake up all closures on a wait list. + */ +static inline void closure_wake_up(struct closure_waitlist *list) +{ + smp_mb(); + __closure_wake_up(list); +} + +/* + * Wait on an event, synchronously or asynchronously - analogous to wait_event() + * but for closures. + * + * The loop is oddly structured so as to avoid a race; we must check the + * condition again after we've added ourself to the waitlist. We know if we were + * already on the waitlist because closure_wait() returns false; thus, we only + * schedule or break if closure_wait() returns false. If it returns true, we + * just loop again - rechecking the condition. + * + * The __closure_wake_up() is necessary because we may race with the event + * becoming true; i.e. we see event false -> wait -> recheck condition, but the + * thread that made the event true may have called closure_wake_up() before we + * added ourself to the wait list. + * + * We have to call closure_sync() at the end instead of just + * __closure_end_sleep() because a different thread might've called + * closure_wake_up() before us and gotten preempted before they dropped the + * refcount on our closure. If this was a stack allocated closure, that would be + * bad. + */ +#define __closure_wait_event(list, cl, condition, _block) \ +({ \ + bool block = _block; \ + typeof(condition) ret; \ + \ + while (1) { \ + ret = (condition); \ + if (ret) { \ + __closure_wake_up(list); \ + if (block) \ + closure_sync(cl); \ + \ + break; \ + } \ + \ + if (block) \ + __closure_start_sleep(cl); \ + \ + if (!closure_wait(list, cl)) { \ + if (!block) \ + break; \ + \ + schedule(); \ + } \ + } \ + \ + ret; \ +}) + +/** + * closure_wait_event() - wait on a condition, synchronously or asynchronously. + * @list: the wait list to wait on + * @cl: the closure that is doing the waiting + * @condition: a C expression for the event to wait for + * + * If the closure is in blocking mode, sleeps until the @condition evaluates to + * true - exactly like wait_event(). + * + * If the closure is not in blocking mode, waits asynchronously; if the + * condition is currently false the @cl is put onto @list and returns. @list + * owns a refcount on @cl; closure_sync() or continue_at() may be used later to + * wait for another thread to wake up @list, which drops the refcount on @cl. + * + * Returns the value of @condition; @cl will be on @list iff @condition was + * false. + * + * closure_wake_up(@list) must be called after changing any variable that could + * cause @condition to become true. + */ +#define closure_wait_event(list, cl, condition) \ + __closure_wait_event(list, cl, condition, closure_blocking(cl)) + +#define closure_wait_event_async(list, cl, condition) \ + __closure_wait_event(list, cl, condition, false) + +#define closure_wait_event_sync(list, cl, condition) \ + __closure_wait_event(list, cl, condition, true) + +static inline void set_closure_fn(struct closure *cl, closure_fn *fn, + struct workqueue_struct *wq) +{ + BUG_ON(object_is_on_stack(cl)); + closure_set_ip(cl); + cl->fn = fn; + cl->wq = wq; + /* between atomic_dec() in closure_put() */ + smp_mb__before_atomic_dec(); +} + +#define continue_at(_cl, _fn, _wq) \ +do { \ + set_closure_fn(_cl, _fn, _wq); \ + closure_sub(_cl, CLOSURE_RUNNING + 1); \ + return; \ +} while (0) + +#define closure_return(_cl) continue_at((_cl), NULL, NULL) + +#define continue_at_nobarrier(_cl, _fn, _wq) \ +do { \ + set_closure_fn(_cl, _fn, _wq); \ + closure_queue(cl); \ + return; \ +} while (0) + +#define closure_return_with_destructor(_cl, _destructor) \ +do { \ + set_closure_fn(_cl, _destructor, NULL); \ + closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1); \ + return; \ +} while (0) + +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); +} + +static inline void closure_trylock_call(struct closure *cl, closure_fn fn, + struct workqueue_struct *wq, + struct closure *parent) +{ + if (closure_trylock(cl, parent)) + continue_at_nobarrier(cl, fn, wq); +} + +#endif /* _LINUX_CLOSURE_H */ |