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

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Date:   Mon,  2 Jan 2017 20:41:14 +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>
Subject: [PATCH 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 4c0fbb0..233d5cb 100644
--- a/drivers/hv/hv_util.c
+++ b/drivers/hv/hv_util.c
@@ -186,6 +186,9 @@ static void hv_set_host_time(struct work_struct *work)
 	u64 newtime;
 	struct timespec64 host_ts, our_ts;
 	struct timex txc = {0};
+	unsigned long flags;
+
+	local_irq_save(flags);
 
 	wrk = container_of(work, struct adj_time_work, work);
 
@@ -214,6 +217,7 @@ static void hv_set_host_time(struct work_struct *work)
 
 	/* Try adjusting time by using phase adjustment if possible */
 	if (abs(delta) > MAXPHASE) {
+		local_irq_restore(flags);
 		do_settimeofday64(&host_ts);
 		return;
 	}
@@ -225,6 +229,8 @@ static void hv_set_host_time(struct work_struct *work)
 	txc.status = STA_PLL;
 	txc.offset = delta;
 	do_adjtimex(&txc);
+
+	local_irq_restore(flags);
 }
 
 /*
-- 
2.9.3