141bcf63983b8bac15468174f63ed0edc7"

// SPDX-License-Identifier: GPL-2.0-only
#define pr_fmt(fmt) "%s: " fmt, __func__

#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/wait.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/percpu-refcount.h>

/*
 * Initially, a percpu refcount is just a set of percpu counters. Initially, we
 * don't try to detect the ref hitting 0 - which means that get/put can just
 * increment or decrement the local counter. Note that the counter on a
 * particular cpu can (and will) wrap - this is fine, when we go to shutdown the
 * percpu counters will all sum to the correct value
 *
 * (More precisely: because modular arithmetic is commutative the sum of all the
 * percpu_count vars will be equal to what it would have been if all the gets
 * and puts were done to a single integer, even if some of the percpu integers
 * overflow or underflow).
 *
 * The real trick to implementing percpu refcounts is shutdown. We can't detect
 * the ref hitting 0 on every put - this would require global synchronization
 * and defeat the whole purpose of using percpu refs.
 *
 * What we do is require the user to keep track of the initial refcount; we know
 * the ref can't hit 0 before the user drops the initial ref, so as long as we
 * convert to non percpu mode before the initial ref is dropped everything
 * works.
 *
 * Converting to non percpu mode is done with some RCUish stuff in
 * percpu_ref_kill. Additionally, we need a bias value so that the
 * atomic_long_t can't hit 0 before we've added up all the percpu refs.
 */

#define PERCPU_COUNT_BIAS	(1LU << (BITS_PER_LONG - 1))

static DEFINE_SPINLOCK(percpu_ref_switch_lock);
static DECLARE_WAIT_QUEUE_HEAD(percpu_ref_switch_waitq);

static unsigned long __percpu *percpu_count_ptr(struct percpu_ref *ref)
{
	return (unsigned long __percpu *)
		(ref->percpu_count_ptr & ~__PERCPU_REF_ATOMIC_DEAD);
}

/**
 * percpu_ref_init - initialize a percpu refcount
 * @ref: percpu_ref to initialize
 * @release: function which will be called when refcount hits 0
 * @flags: PERCPU_REF_INIT_* flags
 * @gfp: allocation mask to use
 *
 * Initializes @ref.  @ref starts out in percpu mode with a refcount of 1 unless
 * @flags contains PERCPU_REF_INIT_ATOMIC or PERCPU_REF_INIT_DEAD.  These flags
 * change the start state to atomic with the latter setting the initial refcount
 * to 0.  See the definitions of PERCPU_REF_INIT_* flags for flag behaviors.
 *
 * Note that @release must not sleep - it may potentially be called from RCU
 * callback context by percpu_ref_kill().
 */
int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
		    unsigned int flags, gfp_t gfp)
{
	size_t align = max_t(size_t, 1 << __PERCPU_REF_FLAG_BITS,
			     __alignof__(unsigned long));
	unsigned long start_count = 0;
	struct percpu_ref_data *data;

	ref->percpu_count_ptr = (unsigned long)
		__alloc_percpu_gfp(sizeof(unsigned long), align, gfp);
	if (!ref->percpu_count_ptr)
		return -ENOMEM;

	data = kzalloc(sizeof(*ref->data), gfp);
	if (!data) {
		free_percpu((void __percpu *)ref->percpu_count_ptr);
		return -ENOMEM;
	}

	data->force_atomic = flags & PERCPU_REF_INIT_ATOMIC;
	data->allow_reinit = flags & PERCPU_REF_ALLOW_REINIT;

	if (flags & (PERCPU_REF_INIT_ATOMIC | PERCPU_REF_INIT_DEAD)) {
		ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
		data->allow_reinit = true;
	} else {
		start_count += PERCPU_COUNT_BIAS;
	}

	if (flags & PERCPU_REF_INIT_DEAD)
		ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
	else
		start_count++;

	atomic_long_set(&data->count, start_count);

	data->release = release;
	data->confirm_switch = NULL;
	data->ref = ref;
	ref->data = data;
	return 0;
}
EXPORT_SYMBOL_GPL(percpu_ref_init);

static void __percpu_ref_exi