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Revision a0cff57bb2a41cb9cbf13d3203097b4156d8c0ae authored by Davidlohr Bueso on 13 September 2017, 20:08:21 UTC, committed by Paolo Bonzini on 15 September 2017, 14:57:12 UTC 
kvm,x86: Fix apf_task_wake_one() wq serialization
 
During code inspection, the following potential race was seen:

CPU0   	    		    	     	CPU1
kvm_async_pf_task_wait			apf_task_wake_one
					  [L] swait_active(&n->wq)
  [S] prepare_to_swait(&n.wq)
  [L] if (!hlist_unhahed(&n.link))
	schedule()			  [S] hlist_del_init(&n->link);

Properly serialize swait_active() checks such that a wakeup is
not missed.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1 parent cc1b468
Raw File
rtc-sun4v.c 
/* rtc-sun4v.c: Hypervisor based RTC for SUN4V systems.
 *
 * Author: David S. Miller
 * License: GPL
 *
 * Copyright (C) 2008 David S. Miller <davem@davemloft.net>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/rtc.h>
#include <linux/platform_device.h>

#include <asm/hypervisor.h>

static unsigned long hypervisor_get_time(void)
{
	unsigned long ret, time;
	int retries = 10000;

retry:
	ret = sun4v_tod_get(&time);
	if (ret == HV_EOK)
		return time;
	if (ret == HV_EWOULDBLOCK) {
		if (--retries > 0) {
			udelay(100);
			goto retry;
		}
		pr_warn("tod_get() timed out.\n");
		return 0;
	}
	pr_warn("tod_get() not supported.\n");
	return 0;
}

static int sun4v_read_time(struct device *dev, struct rtc_time *tm)
{
	rtc_time_to_tm(hypervisor_get_time(), tm);
	return 0;
}

static int hypervisor_set_time(unsigned long secs)
{
	unsigned long ret;
	int retries = 10000;

retry:
	ret = sun4v_tod_set(secs);
	if (ret == HV_EOK)
		return 0;
	if (ret == HV_EWOULDBLOCK) {
		if (--retries > 0) {
			udelay(100);
			goto retry;
		}
		pr_warn("tod_set() timed out.\n");
		return -EAGAIN;
	}
	pr_warn("tod_set() not supported.\n");
	return -EOPNOTSUPP;
}

static int sun4v_set_time(struct device *dev, struct rtc_time *tm)
{
	unsigned long secs;
	int err;

	err = rtc_tm_to_time(tm, &secs);
	if (err)
		return err;

	return hypervisor_set_time(secs);
}

static const struct rtc_class_ops sun4v_rtc_ops = {
	.read_time	= sun4v_read_time,
	.set_time	= sun4v_set_time,
};

static int __init sun4v_rtc_probe(struct platform_device *pdev)
{
	struct rtc_device *rtc;

	rtc = devm_rtc_device_register(&pdev->dev, "sun4v",
				&sun4v_rtc_ops, THIS_MODULE);
	if (IS_ERR(rtc))
		return PTR_ERR(rtc);

	platform_set_drvdata(pdev, rtc);
	return 0;
}

static struct platform_driver sun4v_rtc_driver = {
	.driver		= {
		.name	= "rtc-sun4v",
	},
};

builtin_platform_driver_probe(sun4v_rtc_driver, sun4v_rtc_probe);
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