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As pointed out by Linus, closure_sync() was racy; we could skip blocking immediately after a get() and a put(), but then that would skip any barrier corresponding to the other thread's put() barrier. To fix this, always do the full __closure_sync() sequence whenever any get() has happened and the closure might have been used by other threads. Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
211 lines
4.6 KiB
C
211 lines
4.6 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Asynchronous refcounty things
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*
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* Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
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* Copyright 2012 Google, Inc.
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*/
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#include <linux/closure.h>
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#include <linux/debugfs.h>
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#include <linux/export.h>
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#include <linux/rcupdate.h>
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#include <linux/seq_file.h>
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#include <linux/sched/debug.h>
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static inline void closure_put_after_sub(struct closure *cl, int flags)
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{
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int r = flags & CLOSURE_REMAINING_MASK;
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BUG_ON(flags & CLOSURE_GUARD_MASK);
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BUG_ON(!r && (flags & ~CLOSURE_DESTRUCTOR));
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if (!r) {
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smp_acquire__after_ctrl_dep();
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cl->closure_get_happened = false;
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if (cl->fn && !(flags & CLOSURE_DESTRUCTOR)) {
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atomic_set(&cl->remaining,
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CLOSURE_REMAINING_INITIALIZER);
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closure_queue(cl);
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} else {
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struct closure *parent = cl->parent;
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closure_fn *destructor = cl->fn;
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closure_debug_destroy(cl);
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if (destructor)
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destructor(cl);
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if (parent)
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closure_put(parent);
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}
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}
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}
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/* For clearing flags with the same atomic op as a put */
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void closure_sub(struct closure *cl, int v)
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{
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closure_put_after_sub(cl, atomic_sub_return_release(v, &cl->remaining));
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}
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EXPORT_SYMBOL(closure_sub);
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/*
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* closure_put - decrement a closure's refcount
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*/
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void closure_put(struct closure *cl)
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{
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closure_put_after_sub(cl, atomic_dec_return_release(&cl->remaining));
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}
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EXPORT_SYMBOL(closure_put);
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/*
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* closure_wake_up - wake up all closures on a wait list, without memory barrier
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*/
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void __closure_wake_up(struct closure_waitlist *wait_list)
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{
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struct llist_node *list;
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struct closure *cl, *t;
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struct llist_node *reverse = NULL;
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list = llist_del_all(&wait_list->list);
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/* We first reverse the list to preserve FIFO ordering and fairness */
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reverse = llist_reverse_order(list);
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/* Then do the wakeups */
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llist_for_each_entry_safe(cl, t, reverse, list) {
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closure_set_waiting(cl, 0);
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closure_sub(cl, CLOSURE_WAITING + 1);
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}
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}
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EXPORT_SYMBOL(__closure_wake_up);
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/**
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* closure_wait - add a closure to a waitlist
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* @waitlist: will own a ref on @cl, which will be released when
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* closure_wake_up() is called on @waitlist.
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* @cl: closure pointer.
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*
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*/
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bool closure_wait(struct closure_waitlist *waitlist, struct closure *cl)
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{
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if (atomic_read(&cl->remaining) & CLOSURE_WAITING)
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return false;
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cl->closure_get_happened = true;
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closure_set_waiting(cl, _RET_IP_);
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atomic_add(CLOSURE_WAITING + 1, &cl->remaining);
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llist_add(&cl->list, &waitlist->list);
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return true;
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}
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EXPORT_SYMBOL(closure_wait);
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struct closure_syncer {
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struct task_struct *task;
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int done;
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};
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static void closure_sync_fn(struct closure *cl)
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{
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struct closure_syncer *s = cl->s;
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struct task_struct *p;
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rcu_read_lock();
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p = READ_ONCE(s->task);
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s->done = 1;
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wake_up_process(p);
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rcu_read_unlock();
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}
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void __sched __closure_sync(struct closure *cl)
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{
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struct closure_syncer s = { .task = current };
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cl->s = &s;
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continue_at(cl, closure_sync_fn, NULL);
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while (1) {
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set_current_state(TASK_UNINTERRUPTIBLE);
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if (s.done)
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break;
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schedule();
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}
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__set_current_state(TASK_RUNNING);
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}
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EXPORT_SYMBOL(__closure_sync);
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#ifdef CONFIG_DEBUG_CLOSURES
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static LIST_HEAD(closure_list);
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static DEFINE_SPINLOCK(closure_list_lock);
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void closure_debug_create(struct closure *cl)
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{
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unsigned long flags;
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BUG_ON(cl->magic == CLOSURE_MAGIC_ALIVE);
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cl->magic = CLOSURE_MAGIC_ALIVE;
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spin_lock_irqsave(&closure_list_lock, flags);
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list_add(&cl->all, &closure_list);
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spin_unlock_irqrestore(&closure_list_lock, flags);
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}
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EXPORT_SYMBOL(closure_debug_create);
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void closure_debug_destroy(struct closure *cl)
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{
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unsigned long flags;
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BUG_ON(cl->magic != CLOSURE_MAGIC_ALIVE);
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cl->magic = CLOSURE_MAGIC_DEAD;
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spin_lock_irqsave(&closure_list_lock, flags);
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list_del(&cl->all);
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spin_unlock_irqrestore(&closure_list_lock, flags);
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}
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EXPORT_SYMBOL(closure_debug_destroy);
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static int debug_show(struct seq_file *f, void *data)
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{
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struct closure *cl;
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spin_lock_irq(&closure_list_lock);
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list_for_each_entry(cl, &closure_list, all) {
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int r = atomic_read(&cl->remaining);
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seq_printf(f, "%p: %pS -> %pS p %p r %i ",
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cl, (void *) cl->ip, cl->fn, cl->parent,
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r & CLOSURE_REMAINING_MASK);
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seq_printf(f, "%s%s\n",
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test_bit(WORK_STRUCT_PENDING_BIT,
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work_data_bits(&cl->work)) ? "Q" : "",
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r & CLOSURE_RUNNING ? "R" : "");
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if (r & CLOSURE_WAITING)
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seq_printf(f, " W %pS\n",
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(void *) cl->waiting_on);
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seq_puts(f, "\n");
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}
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spin_unlock_irq(&closure_list_lock);
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return 0;
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}
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DEFINE_SHOW_ATTRIBUTE(debug);
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static int __init closure_debug_init(void)
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{
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debugfs_create_file("closures", 0400, NULL, NULL, &debug_fops);
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return 0;
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}
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late_initcall(closure_debug_init)
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#endif
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