linux-kernel - [PATCH 1/8] Drivers: hv: vmbus: don't loose HVMSG_TIMER

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Message-Id: <1456528402-21982-1-git-send-email-kys@microsoft.com>
Date:	Fri, 26 Feb 2016 15:13:15 -0800
From:	"K. Y. Srinivasan" <kys@...rosoft.com>
To:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
	vkuznets@...hat.com, jasowang@...hat.com
Cc:	"K. Y. Srinivasan" <kys@...rosoft.com>
Subject: [PATCH 1/8] Drivers: hv: vmbus: don't loose HVMSG_TIMER_EXPIRED messages

From: Vitaly Kuznetsov <vkuznets@...hat.com>

We must handle HVMSG_TIMER_EXPIRED messages in the interrupt context
and we offload all the rest to vmbus_on_msg_dpc() tasklet. This functions
loops to see if there are new messages pending. In case we'll ever see
HVMSG_TIMER_EXPIRED message there we're going to lose it as we can't
handle it from there. Avoid looping in vmbus_on_msg_dpc(), we're OK
with handling one message per interrupt.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Reviewed-by: Radim Kr.má<rkrcmar@...hat.com>
Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
---
 drivers/hv/vmbus_drv.c |   68 +++++++++++++++++++++++------------------------
 1 files changed, 33 insertions(+), 35 deletions(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 063e5f5..30ea8ad 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -740,51 +740,49 @@ static void vmbus_on_msg_dpc(unsigned long data)
 	struct vmbus_channel_message_table_entry *entry;
 	struct onmessage_work_context *ctx;
 
-	while (1) {
-		if (msg->header.message_type == HVMSG_NONE)
-			/* no msg */
-			break;
+	if (msg->header.message_type == HVMSG_NONE)
+		/* no msg */
+		return;
 
-		hdr = (struct vmbus_channel_message_header *)msg->u.payload;
+	hdr = (struct vmbus_channel_message_header *)msg->u.payload;
 
-		if (hdr->msgtype >= CHANNELMSG_COUNT) {
-			WARN_ONCE(1, "unknown msgtype=%d\n", hdr->msgtype);
-			goto msg_handled;
-		}
+	if (hdr->msgtype >= CHANNELMSG_COUNT) {
+		WARN_ONCE(1, "unknown msgtype=%d\n", hdr->msgtype);
+		goto msg_handled;
+	}
 
-		entry = &channel_message_table[hdr->msgtype];
-		if (entry->handler_type	== VMHT_BLOCKING) {
-			ctx = kmalloc(sizeof(*ctx), GFP_ATOMIC);
-			if (ctx == NULL)
-				continue;
+	entry = &channel_message_table[hdr->msgtype];
+	if (entry->handler_type	== VMHT_BLOCKING) {
+		ctx = kmalloc(sizeof(*ctx), GFP_ATOMIC);
+		if (ctx == NULL)
+			return;
 
-			INIT_WORK(&ctx->work, vmbus_onmessage_work);
-			memcpy(&ctx->msg, msg, sizeof(*msg));
+		INIT_WORK(&ctx->work, vmbus_onmessage_work);
+		memcpy(&ctx->msg, msg, sizeof(*msg));
 
-			queue_work(vmbus_connection.work_queue, &ctx->work);
-		} else
-			entry->message_handler(hdr);
+		queue_work(vmbus_connection.work_queue, &ctx->work);
+	} else
+		entry->message_handler(hdr);
 
 msg_handled:
-		msg->header.message_type = HVMSG_NONE;
+	msg->header.message_type = HVMSG_NONE;
+
+	/*
+	 * Make sure the write to MessageType (ie set to
+	 * HVMSG_NONE) happens before we read the
+	 * MessagePending and EOMing. Otherwise, the EOMing
+	 * will not deliver any more messages since there is
+	 * no empty slot
+	 */
+	mb();
 
+	if (msg->header.message_flags.msg_pending) {
 		/*
-		 * Make sure the write to MessageType (ie set to
-		 * HVMSG_NONE) happens before we read the
-		 * MessagePending and EOMing. Otherwise, the EOMing
-		 * will not deliver any more messages since there is
-		 * no empty slot
+		 * This will cause message queue rescan to
+		 * possibly deliver another msg from the
+		 * hypervisor
 		 */
-		mb();
-
-		if (msg->header.message_flags.msg_pending) {
-			/*
-			 * This will cause message queue rescan to
-			 * possibly deliver another msg from the
-			 * hypervisor
-			 */
-			wrmsrl(HV_X64_MSR_EOM, 0);
-		}
+		wrmsrl(HV_X64_MSR_EOM, 0);
 	}
 }
 
-- 
1.7.4.1