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From:   kys@linuxonhyperv.com
To:     gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
        devel@linuxdriverproject.org, olaf@aepfle.de, apw@canonical.com,
        jasowang@redhat.com, sthemmin@microsoft.com,
        Michael.H.Kelley@microsoft.com, vkuznets@redhat.com
Cc:     Dexuan Cui <decui@microsoft.com>, stable@vger.kernel.org,
        "K . Y . Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>
Subject: [PATCH 1/2] Drivers: hv: vmbus: Use get/put_cpu() in vmbus_connect()
Date:   Mon, 17 Sep 2018 04:14:54 +0000
Message-Id: <20180917041455.11455-1-kys@linuxonhyperv.com>
In-Reply-To: <20180917041352.11402-1-kys@linuxonhyperv.com>
References: <20180917041352.11402-1-kys@linuxonhyperv.com>
Reply-To: kys@microsoft.com
Sender: linux-kernel-owner@vger.kernel.org
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From: Dexuan Cui <decui@microsoft.com>

With CONFIG_DEBUG_PREEMPT=y, I always see this warning:
BUG: using smp_processor_id() in preemptible [00000000]

Fix the false warning by using get/put_cpu().

Here vmbus_connect() sends a message to the host and waits for the
host's response. The host will deliver the response message and an
interrupt on CPU msg->target_vcpu, and later the interrupt handler
will wake up vmbus_connect(). vmbus_connect() doesn't really have
to run on the same cpu as CPU msg->target_vcpu, so it's safe to
call put_cpu() just here.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Cc: stable@vger.kernel.org
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
---
 drivers/hv/connection.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index ced041899456..f4d08c8ac7f8 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -76,6 +76,7 @@ static int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo,
 					__u32 version)
 {
 	int ret = 0;
+	unsigned int cur_cpu;
 	struct vmbus_channel_initiate_contact *msg;
 	unsigned long flags;
 
@@ -118,9 +119,10 @@ static int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo,
 	 * the CPU attempting to connect may not be CPU 0.
 	 */
 	if (version >= VERSION_WIN8_1) {
-		msg->target_vcpu =
-			hv_cpu_number_to_vp_number(smp_processor_id());
-		vmbus_connection.connect_cpu = smp_processor_id();
+		cur_cpu = get_cpu();
+		msg->target_vcpu = hv_cpu_number_to_vp_number(cur_cpu);
+		vmbus_connection.connect_cpu = cur_cpu;
+		put_cpu();
 	} else {
 		msg->target_vcpu = 0;
 		vmbus_connection.connect_cpu = 0;
-- 
2.18.0