379 lines
12 KiB
C
379 lines
12 KiB
C
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/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_CLOSURE_H
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#define _LINUX_CLOSURE_H
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#include <linux/llist.h>
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#include <linux/sched.h>
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#include <linux/sched/task_stack.h>
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#include <linux/workqueue.h>
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/*
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* Closure is perhaps the most overused and abused term in computer science, but
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* since I've been unable to come up with anything better you're stuck with it
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* again.
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*
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* What are closures?
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*
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* They embed a refcount. The basic idea is they count "things that are in
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* progress" - in flight bios, some other thread that's doing something else -
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* anything you might want to wait on.
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*
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* The refcount may be manipulated with closure_get() and closure_put().
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* closure_put() is where many of the interesting things happen, when it causes
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* the refcount to go to 0.
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*
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* Closures can be used to wait on things both synchronously and asynchronously,
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* and synchronous and asynchronous use can be mixed without restriction. To
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* wait synchronously, use closure_sync() - you will sleep until your closure's
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* refcount hits 1.
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*
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* To wait asynchronously, use
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* continue_at(cl, next_function, workqueue);
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*
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* passing it, as you might expect, the function to run when nothing is pending
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* and the workqueue to run that function out of.
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*
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* continue_at() also, critically, requires a 'return' immediately following the
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* location where this macro is referenced, to return to the calling function.
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* There's good reason for this.
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*
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* To use safely closures asynchronously, they must always have a refcount while
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* they are running owned by the thread that is running them. Otherwise, suppose
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* you submit some bios and wish to have a function run when they all complete:
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*
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* foo_endio(struct bio *bio)
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* {
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* closure_put(cl);
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* }
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*
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* closure_init(cl);
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*
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* do_stuff();
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* closure_get(cl);
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* bio1->bi_endio = foo_endio;
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* bio_submit(bio1);
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*
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* do_more_stuff();
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* closure_get(cl);
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* bio2->bi_endio = foo_endio;
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* bio_submit(bio2);
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*
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* continue_at(cl, complete_some_read, system_wq);
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*
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* If closure's refcount started at 0, complete_some_read() could run before the
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* second bio was submitted - which is almost always not what you want! More
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* importantly, it wouldn't be possible to say whether the original thread or
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* complete_some_read()'s thread owned the closure - and whatever state it was
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* associated with!
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*
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* So, closure_init() initializes a closure's refcount to 1 - and when a
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* closure_fn is run, the refcount will be reset to 1 first.
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*
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* Then, the rule is - if you got the refcount with closure_get(), release it
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* with closure_put() (i.e, in a bio->bi_endio function). If you have a refcount
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* on a closure because you called closure_init() or you were run out of a
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* closure - _always_ use continue_at(). Doing so consistently will help
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* eliminate an entire class of particularly pernicious races.
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*
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* Lastly, you might have a wait list dedicated to a specific event, and have no
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* need for specifying the condition - you just want to wait until someone runs
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* closure_wake_up() on the appropriate wait list. In that case, just use
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* closure_wait(). It will return either true or false, depending on whether the
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* closure was already on a wait list or not - a closure can only be on one wait
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* list at a time.
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*
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* Parents:
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*
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* closure_init() takes two arguments - it takes the closure to initialize, and
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* a (possibly null) parent.
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*
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* If parent is non null, the new closure will have a refcount for its lifetime;
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* a closure is considered to be "finished" when its refcount hits 0 and the
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* function to run is null. Hence
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*
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* continue_at(cl, NULL, NULL);
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*
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* returns up the (spaghetti) stack of closures, precisely like normal return
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* returns up the C stack. continue_at() with non null fn is better thought of
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* as doing a tail call.
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*
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* All this implies that a closure should typically be embedded in a particular
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* struct (which its refcount will normally control the lifetime of), and that
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* struct can very much be thought of as a stack frame.
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*/
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struct closure;
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struct closure_syncer;
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typedef void (closure_fn) (struct closure *);
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extern struct dentry *bcache_debug;
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struct closure_waitlist {
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struct llist_head list;
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};
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enum closure_state {
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/*
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* CLOSURE_WAITING: Set iff the closure is on a waitlist. Must be set by
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* the thread that owns the closure, and cleared by the thread that's
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* waking up the closure.
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*
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* The rest are for debugging and don't affect behaviour:
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*
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* CLOSURE_RUNNING: Set when a closure is running (i.e. by
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* closure_init() and when closure_put() runs then next function), and
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* must be cleared before remaining hits 0. Primarily to help guard
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* against incorrect usage and accidentally transferring references.
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* continue_at() and closure_return() clear it for you, if you're doing
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* something unusual you can use closure_set_dead() which also helps
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* annotate where references are being transferred.
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*/
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CLOSURE_BITS_START = (1U << 26),
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CLOSURE_DESTRUCTOR = (1U << 26),
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CLOSURE_WAITING = (1U << 28),
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CLOSURE_RUNNING = (1U << 30),
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};
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#define CLOSURE_GUARD_MASK \
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((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_RUNNING) << 1)
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#define CLOSURE_REMAINING_MASK (CLOSURE_BITS_START - 1)
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#define CLOSURE_REMAINING_INITIALIZER (1|CLOSURE_RUNNING)
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struct closure {
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union {
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struct {
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struct workqueue_struct *wq;
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struct closure_syncer *s;
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struct llist_node list;
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closure_fn *fn;
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};
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struct work_struct work;
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};
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struct closure *parent;
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atomic_t remaining;
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#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
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#define CLOSURE_MAGIC_DEAD 0xc054dead
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#define CLOSURE_MAGIC_ALIVE 0xc054a11e
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unsigned int magic;
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struct list_head all;
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unsigned long ip;
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unsigned long waiting_on;
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#endif
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};
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void closure_sub(struct closure *cl, int v);
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void closure_put(struct closure *cl);
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void __closure_wake_up(struct closure_waitlist *list);
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bool closure_wait(struct closure_waitlist *list, struct closure *cl);
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void __closure_sync(struct closure *cl);
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/**
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* closure_sync - sleep until a closure a closure has nothing left to wait on
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*
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* Sleeps until the refcount hits 1 - the thread that's running the closure owns
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* the last refcount.
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*/
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static inline void closure_sync(struct closure *cl)
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{
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if ((atomic_read(&cl->remaining) & CLOSURE_REMAINING_MASK) != 1)
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__closure_sync(cl);
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}
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#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
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void closure_debug_init(void);
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void closure_debug_create(struct closure *cl);
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void closure_debug_destroy(struct closure *cl);
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#else
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static inline void closure_debug_init(void) {}
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static inline void closure_debug_create(struct closure *cl) {}
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static inline void closure_debug_destroy(struct closure *cl) {}
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#endif
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static inline void closure_set_ip(struct closure *cl)
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{
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#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
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cl->ip = _THIS_IP_;
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#endif
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}
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static inline void closure_set_ret_ip(struct closure *cl)
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{
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#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
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cl->ip = _RET_IP_;
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#endif
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}
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static inline void closure_set_waiting(struct closure *cl, unsigned long f)
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{
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#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
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cl->waiting_on = f;
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#endif
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}
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static inline void closure_set_stopped(struct closure *cl)
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{
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atomic_sub(CLOSURE_RUNNING, &cl->remaining);
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}
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static inline void set_closure_fn(struct closure *cl, closure_fn *fn,
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struct workqueue_struct *wq)
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{
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closure_set_ip(cl);
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cl->fn = fn;
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cl->wq = wq;
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/* between atomic_dec() in closure_put() */
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smp_mb__before_atomic();
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}
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static inline void closure_queue(struct closure *cl)
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{
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struct workqueue_struct *wq = cl->wq;
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/**
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* Changes made to closure, work_struct, or a couple of other structs
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* may cause work.func not pointing to the right location.
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*/
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BUILD_BUG_ON(offsetof(struct closure, fn)
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!= offsetof(struct work_struct, func));
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if (wq) {
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INIT_WORK(&cl->work, cl->work.func);
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BUG_ON(!queue_work(wq, &cl->work));
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} else
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cl->fn(cl);
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}
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/**
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* closure_get - increment a closure's refcount
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*/
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static inline void closure_get(struct closure *cl)
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{
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#ifdef CONFIG_BCACHE_CLOSURES_DEBUG
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BUG_ON((atomic_inc_return(&cl->remaining) &
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CLOSURE_REMAINING_MASK) <= 1);
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#else
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atomic_inc(&cl->remaining);
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#endif
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}
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/**
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* closure_init - Initialize a closure, setting the refcount to 1
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* @cl: closure to initialize
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* @parent: parent of the new closure. cl will take a refcount on it for its
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* lifetime; may be NULL.
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*/
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static inline void closure_init(struct closure *cl, struct closure *parent)
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{
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memset(cl, 0, sizeof(struct closure));
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cl->parent = parent;
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if (parent)
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closure_get(parent);
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atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
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closure_debug_create(cl);
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closure_set_ip(cl);
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}
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static inline void closure_init_stack(struct closure *cl)
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{
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memset(cl, 0, sizeof(struct closure));
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atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
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}
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/**
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* closure_wake_up - wake up all closures on a wait list,
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* with memory barrier
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*/
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static inline void closure_wake_up(struct closure_waitlist *list)
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{
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/* Memory barrier for the wait list */
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smp_mb();
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__closure_wake_up(list);
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}
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/**
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* continue_at - jump to another function with barrier
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*
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* After @cl is no longer waiting on anything (i.e. all outstanding refs have
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* been dropped with closure_put()), it will resume execution at @fn running out
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* of @wq (or, if @wq is NULL, @fn will be called by closure_put() directly).
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*
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* This is because after calling continue_at() you no longer have a ref on @cl,
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* and whatever @cl owns may be freed out from under you - a running closure fn
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* has a ref on its own closure which continue_at() drops.
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*
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* Note you are expected to immediately return after using this macro.
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*/
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#define continue_at(_cl, _fn, _wq) \
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do { \
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set_closure_fn(_cl, _fn, _wq); \
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closure_sub(_cl, CLOSURE_RUNNING + 1); \
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} while (0)
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/**
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* closure_return - finish execution of a closure
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*
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* This is used to indicate that @cl is finished: when all outstanding refs on
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* @cl have been dropped @cl's ref on its parent closure (as passed to
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* closure_init()) will be dropped, if one was specified - thus this can be
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* thought of as returning to the parent closure.
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*/
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#define closure_return(_cl) continue_at((_cl), NULL, NULL)
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/**
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* continue_at_nobarrier - jump to another function without barrier
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*
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* Causes @fn to be executed out of @cl, in @wq context (or called directly if
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* @wq is NULL).
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*
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* The ref the caller of continue_at_nobarrier() had on @cl is now owned by @fn,
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* thus it's not safe to touch anything protected by @cl after a
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* continue_at_nobarrier().
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*/
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#define continue_at_nobarrier(_cl, _fn, _wq) \
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do { \
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set_closure_fn(_cl, _fn, _wq); \
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closure_queue(_cl); \
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} while (0)
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/**
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* closure_return_with_destructor - finish execution of a closure,
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* with destructor
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*
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* Works like closure_return(), except @destructor will be called when all
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* outstanding refs on @cl have been dropped; @destructor may be used to safely
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* free the memory occupied by @cl, and it is called with the ref on the parent
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* closure still held - so @destructor could safely return an item to a
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* freelist protected by @cl's parent.
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*/
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#define closure_return_with_destructor(_cl, _destructor) \
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do { \
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set_closure_fn(_cl, _destructor, NULL); \
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closure_sub(_cl, CLOSURE_RUNNING - CLOSURE_DESTRUCTOR + 1); \
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} while (0)
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/**
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* closure_call - execute @fn out of a new, uninitialized closure
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*
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* Typically used when running out of one closure, and we want to run @fn
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* asynchronously out of a new closure - @parent will then wait for @cl to
|
||
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|
* 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);
|
||
|
|
}
|
||
|
|
|
||
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|
#endif /* _LINUX_CLOSURE_H */
|