C++ smp_rmb函数代码示例

void skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb)
{
	bool slow;

	if (likely(atomic_read(&skb->users) == 1))
		smp_rmb();
	else if (likely(!atomic_dec_and_test(&skb->users)))
		return;

	slow = lock_sock_fast(sk);
	skb_orphan(skb);
	sk_mem_reclaim_partial(sk);
	unlock_sock_fast(sk, slow);

	/* skb is now orphaned, can be freed outside of locked section */
	trace_kfree_skb(skb, skb_free_datagram_locked);
	__kfree_skb(skb);
}

static inline u16
vlan_dev_get_egress_qos_mask(struct net_device *dev, struct sk_buff *skb)
{
	struct vlan_priority_tci_mapping *mp;

	smp_rmb(); /* coupled with smp_wmb() in vlan_dev_set_egress_priority() */

	mp = vlan_dev_priv(dev)->egress_priority_map[(skb->priority & 0xF)];
	while (mp) {
		if (mp->priority == skb->priority) {
			return mp->vlan_qos; /* This should already be shifted
					      * to mask correctly with the
					      * VLAN's TCI */
		}
		mp = mp->next;
	}
	return 0;
}

void native_cpu_die(unsigned int cpu)
{
	unsigned int i;

	for (i = 0; i < 10; i++) {
		smp_rmb();
		if (per_cpu(cpu_state, cpu) == CPU_DEAD) {
			if (system_state == SYSTEM_RUNNING)
				pr_info("CPU %u is now offline\n", cpu);

			return;
		}

		msleep(100);
	}

	pr_err("CPU %u didn't die...\n", cpu);
}

void
gc_jd_queue_enqueue(gc_jd_queue_t *q, gc_job_desc_t *item)
{
  item->sys.next = 0;
  _mutex_lock(ptr_to_ea(&q->mutex));
  smp_rmb();		// import barrier

  if (q->tail == 0){    // currently empty
    q->tail = q->head = jdp_to_ea(item);
  }
  else {		// not empty, append
    ea_to_jdp(q->tail)->sys.next = jdp_to_ea(item);
    q->tail = jdp_to_ea(item);
  }

  smp_wmb();		// orders stores above before clearing of mutex
  _mutex_unlock(ptr_to_ea(&q->mutex));
}

int __cpuinit boot_secondary(unsigned int cpu, struct task_struct *idle)
{
	unsigned long timeout;

	/*
	 * set synchronisation state between this boot processor
	 * and the secondary one
	 */
	spin_lock(&boot_lock);

	/*
	 * The secondary processor is waiting to be released from
	 * the holding pen - release it, then wait for it to flag
	 * that it has been released by resetting pen_release.
	 *
	 * Note that "pen_release" is the hardware CPU ID, whereas
	 * "cpu" is Linux's internal ID.
	 */
	write_pen_release(cpu);

	/*
	 * Send the secondary CPU a soft interrupt, thereby causing
	 * the boot monitor to read the system wide flags register,
	 * and branch to the address found there.
	 */
	smp_cross_call(cpumask_of(cpu), 1);

	timeout = jiffies + (1 * HZ);
	while (time_before(jiffies, timeout)) {
		smp_rmb();
		if (pen_release == -1)
			break;

		udelay(10);
	}

	/*
	 * now the secondary core is starting up let it run its
	 * calibrations, then wait for it to finish
	 */
	spin_unlock(&boot_lock);

	return pen_release != -1 ? -ENOSYS : 0;
}

static struct dsm_client *dsm_find_client(char *cname)
{
	int i;
	struct dsm_client * client = NULL;

	mutex_lock(&g_dsm_server.mtx_lock);
	smp_rmb();
	for(i=0; i<CLIENT_SIZE; i++){
		if((test_bit(DSM_CLIENT_VAILD_BIT, &g_dsm_server.client_flag[i]))
			&& (!strncasecmp(g_dsm_server.client_list[i]->client_name, cname, CLIENT_NAME_LEN))){
			client = g_dsm_server.client_list[i];
			break;
		}
	}
	mutex_unlock(&g_dsm_server.mtx_lock);
	DSM_LOG_DEBUG("cname: %s find %s\n", cname, client?"success":"failed");

	return client;
}

static void print_buffers(void)
{
	struct print_buffer *buffer;
	struct entry_head *head;
	off_t read_pos;
	int len, ret;

	while (1) {
		buffer = get_next_buffer();
		if (!buffer)
			break;

		read_pos = buffer->read_pos;
		head = buffer->ring + read_pos;
		len = head->len;

		if (len) {
			/* Print out non-empty entry and proceed */
			/* Check if output goes to syslog */
			if (head->dest == RT_PRINT_SYSLOG_STREAM) {
				syslog(head->priority,
				       "%s", head->data);
			} else {
				ret = fwrite(head->data,
					     head->len, 1, head->dest);
				(void)ret;
			}

			read_pos += sizeof(*head) + len;
		} else {
			/* Emptry entries mark the wrap-around */
			read_pos = 0;
		}

		/* Make sure we have read the entry competely before
		   forwarding read_pos */
		smp_rmb();
		buffer->read_pos = read_pos;

		/* Enforce the read_pos update before proceeding */
		smp_wmb();
	}
}

/* allocates a chunk for the reader from filled (and munged) buffer space */
unsigned int comedi_buf_read_alloc(struct comedi_async *async,
                                   unsigned int nbytes)
{
    unsigned int available;

    available = async->munge_count - async->buf_read_alloc_count;
    if (nbytes > available)
        nbytes = available;

    async->buf_read_alloc_count += nbytes;

    /*
     * ensure the async buffer 'counts' are read before we
     * attempt to read data from the read-alloc'ed buffer space
     */
    smp_rmb();

    return nbytes;
}

static int dev_mce_log(struct notifier_block *nb, unsigned long val,
				void *data)
{
	struct mce *mce = (struct mce *)data;
	unsigned int next, entry;

	wmb();
	for (;;) {
		entry = mce_log_get_idx_check(mcelog.next);
		for (;;) {

			/*
			 * When the buffer fills up discard new entries.
			 * Assume that the earlier errors are the more
			 * interesting ones:
			 */
			if (entry >= MCE_LOG_LEN) {
				set_bit(MCE_OVERFLOW,
					(unsigned long *)&mcelog.flags);
				return NOTIFY_OK;
			}
			/* Old left over entry. Skip: */
			if (mcelog.entry[entry].finished) {
				entry++;
				continue;
			}
			break;
		}
		smp_rmb();
		next = entry + 1;
		if (cmpxchg(&mcelog.next, entry, next) == entry)
			break;
	}
	memcpy(mcelog.entry + entry, mce, sizeof(struct mce));
	wmb();
	mcelog.entry[entry].finished = 1;
	wmb();

	/* wake processes polling /dev/mcelog */
	wake_up_interruptible(&mce_chrdev_wait);

	return NOTIFY_OK;
}

static int
virtqueue_num_heads(VuDev *dev, VuVirtq *vq, unsigned int idx)
{
    uint16_t num_heads = vring_avail_idx(vq) - idx;

    /* Check it isn't doing very strange things with descriptor numbers. */
    if (num_heads > vq->vring.num) {
        vu_panic(dev, "Guest moved used index from %u to %u",
                 idx, vq->shadow_avail_idx);
        return -1;
    }
    if (num_heads) {
        /* On success, callers read a descriptor at vq->last_avail_idx.
         * Make sure descriptor read does not bypass avail index read. */
        smp_rmb();
    }

    return num_heads;
}

void mce_log(struct mce *mce)
{
	unsigned next, entry;
	int ret = 0;

	
	trace_mce_record(mce);

	ret = atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, mce);
	if (ret == NOTIFY_STOP)
		return;

	mce->finished = 0;
	wmb();
	for (;;) {
		entry = rcu_dereference_check_mce(mcelog.next);
		for (;;) {

			if (entry >= MCE_LOG_LEN) {
				set_bit(MCE_OVERFLOW,
					(unsigned long *)&mcelog.flags);
				return;
			}
			
			if (mcelog.entry[entry].finished) {
				entry++;
				continue;
			}
			break;
		}
		smp_rmb();
		next = entry + 1;
		if (cmpxchg(&mcelog.next, entry, next) == entry)
			break;
	}
	memcpy(mcelog.entry + entry, mce, sizeof(struct mce));
	wmb();
	mcelog.entry[entry].finished = 1;
	wmb();

	mce->finished = 1;
	set_bit(0, &mce_need_notify);
}

int sti_boot_secondary(unsigned int cpu, struct task_struct *idle)
{
	unsigned long timeout;

	/*
	 * set synchronisation state between this boot processor
	 * and the secondary one
	 */
	spin_lock(&boot_lock);

	/*
	 * The secondary processor is waiting to be released from
	 * the holding pen - release it, then wait for it to flag
	 * that it has been released by resetting pen_release.
	 *
	 * Note that "pen_release" is the hardware CPU ID, whereas
	 * "cpu" is Linux's internal ID.
	 */
	write_pen_release(cpu_logical_map(cpu));

	/*
	 * Send the secondary CPU a soft interrupt, thereby causing
	 * it to jump to the secondary entrypoint.
	 */
	arch_send_wakeup_ipi_mask(cpumask_of(cpu));

	timeout = jiffies + (1 * HZ);
	while (time_before(jiffies, timeout)) {
		smp_rmb();
		if (pen_release == -1)
			break;

		udelay(10);
	}

	/*
	 * now the secondary core is starting up let it run its
	 * calibrations, then wait for it to finish
	 */
	spin_unlock(&boot_lock);

	return pen_release != -1 ? -ENOSYS : 0;
}

static int acpi_aml_readb_kern(void)
{
	int ret;
	struct circ_buf *crc = &acpi_aml_io.in_crc;
	char *p;

	ret = acpi_aml_lock_read(crc, ACPI_AML_IN_KERN);
	if (ret < 0)
		return ret;
	/* sync head before removing cmds */
	smp_rmb();
	p = &crc->buf[crc->tail];
	ret = (int)*p;
	/* sync tail before inserting cmds */
	smp_mb();
	crc->tail = (crc->tail + 1) & (ACPI_AML_BUF_SIZE - 1);
	acpi_aml_unlock_fifo(ACPI_AML_IN_KERN, true);
	return ret;
}

/*
 * This does the RCU processing work from softirq context. 
 */
static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
                                    struct rcu_data *rdp)
{
    if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {
        *rdp->donetail = rdp->curlist;
        rdp->donetail = rdp->curtail;
        rdp->curlist = NULL;
        rdp->curtail = &rdp->curlist;
    }

    local_irq_disable();
    if (rdp->nxtlist && !rdp->curlist) {
        rdp->curlist = rdp->nxtlist;
        rdp->curtail = rdp->nxttail;
        rdp->nxtlist = NULL;
        rdp->nxttail = &rdp->nxtlist;
        local_irq_enable();

        /*
         * start the next batch of callbacks
         */

        /* determine batch number */
        rdp->batch = rcp->cur + 1;
        /* see the comment and corresponding wmb() in
         * the rcu_start_batch()
         */
        smp_rmb();

        if (!rcp->next_pending) {
            /* and start it/schedule start if it's a new batch */
            spin_lock(&rcp->lock);
            rcp->next_pending = 1;
            rcu_start_batch(rcp);
            spin_unlock(&rcp->lock);
        }
    } else {
        local_irq_enable();
    }
    rcu_check_quiescent_state(rcp, rdp);
    if (rdp->donelist)
        rcu_do_batch(rdp);
}

int versatile_boot_secondary(unsigned int cpu, struct task_struct *idle)
{
	unsigned long timeout;

	/*
	 * Set synchronisation state between this boot processor
	 * and the secondary one
	 */
	spin_lock(&boot_lock);

	/*
	 * This is really belt and braces; we hold unintended secondary
	 * CPUs in the holding pen until we're ready for them.  However,
	 * since we haven't sent them a soft interrupt, they shouldn't
	 * be there.
	 */
	write_pen_release(cpu_logical_map(cpu));

	/*
	 * Send the secondary CPU a soft interrupt, thereby causing
	 * the boot monitor to read the system wide flags register,
	 * and branch to the address found there.
	 */
	arch_send_wakeup_ipi_mask(cpumask_of(cpu));

	timeout = jiffies + (1 * HZ);
	while (time_before(jiffies, timeout)) {
		smp_rmb();
		if (pen_release == -1)
			break;

		udelay(10);
	}

	/*
	 * now the secondary core is starting up let it run its
	 * calibrations, then wait for it to finish
	 */
	spin_unlock(&boot_lock);

	return pen_release != -1 ? -ENOSYS : 0;
}