Quelle closure.c Sprache: C

// SPDX-License-Identifier: GPL-2.0
/*
* Asynchronous refcounty things
*
* Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
* Copyright 2012 Google, Inc.
*/

#include <linux/closure.h>
#include <linux/debugfs.h>
#include <linux/export.h>
#include <linux/rcupdate.h>
#include <linux/seq_file.h>
#include <linux/sched/debug.h>

static inline void closure_put_after_sub_checks(int flags)
{
int r = flags & CLOSURE_REMAINING_MASK;

if (WARN(flags & CLOSURE_GUARD_MASK,
   "closure has guard bits set: %x (%u)",
   flags & CLOSURE_GUARD_MASK, (unsigned) __fls(r)))
  r &= ~CLOSURE_GUARD_MASK;

WARN(!r && (flags & ~CLOSURE_DESTRUCTOR),
      "closure ref hit 0 with incorrect flags set: %x (%u)",
      flags & ~CLOSURE_DESTRUCTOR, (unsigned) __fls(flags));
}

static inline void closure_put_after_sub(struct closure *cl, int flags)
{
closure_put_after_sub_checks(flags);

if (!(flags & CLOSURE_REMAINING_MASK)) {
  smp_acquire__after_ctrl_dep();

  cl->closure_get_happened = false;

  if (cl->fn && !(flags & CLOSURE_DESTRUCTOR)) {
   atomic_set(&cl->remaining,
       CLOSURE_REMAINING_INITIALIZER);
   closure_queue(cl);
  } else {
   struct closure *parent = cl->parent;
   closure_fn *destructor = cl->fn;

   closure_debug_destroy(cl);

   if (destructor)
    destructor(&cl->work);

   if (parent)
    closure_put(parent);
  }
}
}

/* For clearing flags with the same atomic op as a put */
void closure_sub(struct closure *cl, int v)
{
closure_put_after_sub(cl, atomic_sub_return_release(v, &cl->remaining));
}
EXPORT_SYMBOL(closure_sub);

/*
* closure_put - decrement a closure's refcount
*/
void closure_put(struct closure *cl)
{
closure_put_after_sub(cl, atomic_dec_return_release(&cl->remaining));
}
EXPORT_SYMBOL(closure_put);

/*
* closure_wake_up - wake up all closures on a wait list, without memory barrier
*/
void __closure_wake_up(struct closure_waitlist *wait_list)
{
struct llist_node *list;
struct closure *cl, *t;
struct llist_node *reverse = NULL;

list = llist_del_all(&wait_list->list);

/* We first reverse the list to preserve FIFO ordering and fairness */
reverse = llist_reverse_order(list);

/* Then do the wakeups */
llist_for_each_entry_safe(cl, t, reverse, list) {
  closure_set_waiting(cl, 0);
  closure_sub(cl, CLOSURE_WAITING + 1);
}
}
EXPORT_SYMBOL(__closure_wake_up);

/**
* closure_wait - add a closure to a waitlist
* @waitlist: will own a ref on @cl, which will be released when
* closure_wake_up() is called on @waitlist.
* @cl: closure pointer.
*
*/
bool closure_wait(struct closure_waitlist *waitlist, struct closure *cl)
{
if (atomic_read(&cl->remaining) & CLOSURE_WAITING)
  return false;

cl->closure_get_happened = true;
closure_set_waiting(cl, _RET_IP_);
atomic_add(CLOSURE_WAITING + 1, &cl->remaining);
llist_add(&cl->list, &waitlist->list);

return true;
}
EXPORT_SYMBOL(closure_wait);

struct closure_syncer {
struct task_struct *task;
int   done;
};

static CLOSURE_CALLBACK(closure_sync_fn)
{
struct closure *cl = container_of(ws, struct closure, work);
struct closure_syncer *s = cl->s;
struct task_struct *p;

rcu_read_lock();
p = READ_ONCE(s->task);
s->done = 1;
wake_up_process(p);
rcu_read_unlock();
}

void __sched __closure_sync(struct closure *cl)
{
struct closure_syncer s = { .task = current };

cl->s = &s;
continue_at(cl, closure_sync_fn, NULL);

while (1) {
  set_current_state(TASK_UNINTERRUPTIBLE);
  if (s.done)
   break;
  schedule();
}

__set_current_state(TASK_RUNNING);
}
EXPORT_SYMBOL(__closure_sync);

/*
* closure_return_sync - finish running a closure, synchronously (i.e. waiting
* for outstanding get()s to finish) and returning once closure refcount is 0.
*
* Unlike closure_sync() this doesn't reinit the ref to 1; subsequent
* closure_get_not_zero() calls waill fail.
*/
void __sched closure_return_sync(struct closure *cl)
{
struct closure_syncer s = { .task = current };

cl->s = &s;
set_closure_fn(cl, closure_sync_fn, NULL);

unsigned flags = atomic_sub_return_release(1 + CLOSURE_RUNNING - CLOSURE_DESTRUCTOR,
         &cl->remaining);

closure_put_after_sub_checks(flags);

if (unlikely(flags & CLOSURE_REMAINING_MASK)) {
  while (1) {
   set_current_state(TASK_UNINTERRUPTIBLE);
   if (s.done)
    break;
   schedule();
  }

  __set_current_state(TASK_RUNNING);
}

if (cl->parent)
  closure_put(cl->parent);
}
EXPORT_SYMBOL(closure_return_sync);

int __sched __closure_sync_timeout(struct closure *cl, unsigned long timeout)
{
struct closure_syncer s = { .task = current };
int ret = 0;

cl->s = &s;
continue_at(cl, closure_sync_fn, NULL);

while (1) {
  set_current_state(TASK_UNINTERRUPTIBLE);
  if (s.done)
   break;
  if (!timeout) {
   /*
* Carefully undo the continue_at() - but only if it
* hasn't completed, i.e. the final closure_put() hasn't
* happened yet:
*/
   unsigned old, new, v = atomic_read(&cl->remaining);
   do {
    old = v;
    if (!old || (old & CLOSURE_RUNNING))
     goto success;

    new = old + CLOSURE_REMAINING_INITIALIZER;
   } while ((v = atomic_cmpxchg(&cl->remaining, old, new)) != old);
   ret = -ETIME;
  }

  timeout = schedule_timeout(timeout);
}
success:
__set_current_state(TASK_RUNNING);
return ret;
}
EXPORT_SYMBOL(__closure_sync_timeout);

#ifdef CONFIG_DEBUG_CLOSURES

static LIST_HEAD(closure_list);
static DEFINE_SPINLOCK(closure_list_lock);

void closure_debug_create(struct closure *cl)
{
unsigned long flags;

BUG_ON(cl->magic == CLOSURE_MAGIC_ALIVE);
cl->magic = CLOSURE_MAGIC_ALIVE;

spin_lock_irqsave(&closure_list_lock, flags);
list_add(&cl->all, &closure_list);
spin_unlock_irqrestore(&closure_list_lock, flags);
}
EXPORT_SYMBOL(closure_debug_create);

void closure_debug_destroy(struct closure *cl)
{
unsigned long flags;

if (cl->magic == CLOSURE_MAGIC_STACK)
  return;

BUG_ON(cl->magic != CLOSURE_MAGIC_ALIVE);
cl->magic = CLOSURE_MAGIC_DEAD;

spin_lock_irqsave(&closure_list_lock, flags);
list_del(&cl->all);
spin_unlock_irqrestore(&closure_list_lock, flags);
}
EXPORT_SYMBOL(closure_debug_destroy);

static int debug_show(struct seq_file *f, void *data)
{
struct closure *cl;

spin_lock_irq(&closure_list_lock);

list_for_each_entry(cl, &closure_list, all) {
  int r = atomic_read(&cl->remaining);

  seq_printf(f, "%p: %pS -> %pS p %p r %i ",
      cl, (void *) cl->ip, cl->fn, cl->parent,
      r & CLOSURE_REMAINING_MASK);

  seq_printf(f, "%s%s\n",
      test_bit(WORK_STRUCT_PENDING_BIT,
        work_data_bits(&cl->work)) ? "Q" : "",
      r & CLOSURE_RUNNING ? "R" : "");

  if (r & CLOSURE_WAITING)
   seq_printf(f, " W %pS\n",
       (void *) cl->waiting_on);

  seq_putc(f, '\n');
}

spin_unlock_irq(&closure_list_lock);
return 0;
}

DEFINE_SHOW_ATTRIBUTE(debug);

static int __init closure_debug_init(void)
{
debugfs_create_file("closures", 0400, NULL, NULL, &debug_fops);
return 0;
}
late_initcall(closure_debug_init)

#endif

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