linux-kernel - [PATCH v2 4/4] hv_util: improve time adjustment accuracy by disabling interrupts

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Date:   Wed,  4 Jan 2017 18:24:39 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     devel@...uxdriverproject.org
Cc:     linux-kernel@...r.kernel.org,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alex Ng <alexng@...rosoft.com>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: [PATCH v2 4/4] hv_util: improve time adjustment accuracy by disabling interrupts

If we happen to receive interrupts during hv_set_host_time() execution
our adjustments may get inaccurate. Make the whole function atomic.
Unfortunately, we can's call do_settimeofday64() with interrupts
disabled as some cross-CPU work is being done but this call happens
very rarely.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 drivers/hv/hv_util.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
index 7e97231..4e50a42 100644
--- a/drivers/hv/hv_util.c
+++ b/drivers/hv/hv_util.c
@@ -187,6 +187,9 @@ static void hv_set_host_time(struct work_struct *work)
 	struct timespec64 host_ts, our_ts;
 	struct timex txc = {0};
 	int ret;
+	unsigned long flags;
+
+	local_irq_save(flags);
 
 	wrk = container_of(work, struct adj_time_work, work);
 
@@ -218,6 +221,7 @@ static void hv_set_host_time(struct work_struct *work)
 	 * ordered to sync our time by the host.
 	 */
 	if (abs(delta) > MAXPHASE || wrk->flags & ICTIMESYNCFLAG_SYNC) {
+		local_irq_restore(flags);
 		do_settimeofday64(&host_ts);
 		return;
 	}
@@ -232,6 +236,8 @@ static void hv_set_host_time(struct work_struct *work)
 	ret = do_adjtimex(&txc);
 	if (ret)
 		pr_debug("Failed to adjust system time: %d\n", ret);
+
+	local_irq_restore(flags);
 }
 
 /*
-- 
2.9.3