![Ingo Molnar](/assets/img/avatar_default.png)
We are going to split <linux/sched/task_stack.h> out of <linux/sched.h>, which will have to be picked up from other headers and a couple of .c files. Create a trivial placeholder <linux/sched/task_stack.h> file that just maps to <linux/sched.h> to make this patch obviously correct and bisectable. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
386 lines
12 KiB
C
386 lines
12 KiB
C
#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;
|
|
typedef void (closure_fn) (struct closure *);
|
|
|
|
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.
|
|
*
|
|
* 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.
|
|
*
|
|
* 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 << 23),
|
|
CLOSURE_DESTRUCTOR = (1 << 23),
|
|
CLOSURE_WAITING = (1 << 25),
|
|
CLOSURE_SLEEPING = (1 << 27),
|
|
CLOSURE_RUNNING = (1 << 29),
|
|
CLOSURE_STACK = (1 << 31),
|
|
};
|
|
|
|
#define CLOSURE_GUARD_MASK \
|
|
((CLOSURE_DESTRUCTOR|CLOSURE_WAITING|CLOSURE_SLEEPING| \
|
|
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;
|
|
|
|
#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
|
|
};
|
|
|
|
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);
|
|
|
|
#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_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);
|
|
}
|
|
|
|
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)
|
|
{
|
|
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();
|
|
}
|
|
|
|
static inline void closure_queue(struct closure *cl)
|
|
{
|
|
struct workqueue_struct *wq = cl->wq;
|
|
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_STACK);
|
|
}
|
|
|
|
/**
|
|
* 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);
|
|
}
|
|
|
|
/**
|
|
* 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).
|
|
*
|
|
* NOTE: This macro expands to a return in the calling function!
|
|
*
|
|
* 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.
|
|
*/
|
|
#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).
|
|
*
|
|
* NOTE: like continue_at(), this macro expands to a return in the caller!
|
|
*
|
|
* 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 - 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 */
|