OSCL-LXR linux-6.0.1/​drivers/​md/​bcache/​closure.h	Source navigation Diff markup Identifier search General search
	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 /* 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 closure *);
 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;
 
 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG
 #define CLOSURE_MAGIC_DEAD  0xc054dead
 #define CLOSURE_MAGIC_ALIVE 0xc054a11e
 
     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);
 
 /**
  * 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)
 {
     if ((atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK) != 1)
         __closure_sync(cl);
 }
 
 #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_set_waiting(struct closure *cl, unsigned long f)
 {
 #ifdef CONFIG_BCACHE_CLOSURES_DEBUG
     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;
     /* between atomic_dec() in closure_put() */
     smp_mb__before_atomic();
 }
 
 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);
 }
 
 /**
  * closure_get - increment a closure's refcount
  */
 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
 }
 
 /**
  * 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)
 {
     memset(cl, 0, sizeof(struct closure));
     cl->parent = parent;
     if (parent)
         closure_get(parent);
 
     atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
 
     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);
 }
 
 /**
  * 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);
 }
 
 /**
  * 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)
 
 /**
  * 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);
 }
 
 #endif /* _LINUX_CLOSURE_H */

This page was automatically generated by the 2.1.0 LXR engine. The LXR team