Drivers: hv: vmbus: Use cpumask_var_t for on-stack cpu mask

A cpumask structure on the stack can cause a warning with
CONFIG_NR_CPUS=8192 (e.g. Ubuntu 16.04 and 18.04 use this):

drivers/hv//channel_mgmt.c: In function ‘init_vp_index’:
drivers/hv//channel_mgmt.c:702:1: warning: the frame size of 1032 bytes
  is larger than 1024 bytes [-Wframe-larger-than=]

Nowadays it looks most distros enable CONFIG_CPUMASK_OFFSTACK=y, and
hence we can work around the warning by using cpumask_var_t.
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/channel_mgmt.c

@@ -594,16 +594,18 @@ static void init_vp_index(struct vmbus_channel *channel, u16 dev_type)
 	bool perf_chn = vmbus_devs[dev_type].perf_device;
 	struct vmbus_channel *primary = channel->primary_channel;
 	int next_node;
-	struct cpumask available_mask;
+	cpumask_var_t available_mask;
 	struct cpumask *alloced_mask;
 
 	if ((vmbus_proto_version == VERSION_WS2008) ||
-	    (vmbus_proto_version == VERSION_WIN7) || (!perf_chn)) {
+	    (vmbus_proto_version == VERSION_WIN7) || (!perf_chn) ||
+	    !alloc_cpumask_var(&available_mask, GFP_KERNEL)) {
 		/*
 		 * Prior to win8, all channel interrupts are
 		 * delivered on cpu 0.
 		 * Also if the channel is not a performance critical
 		 * channel, bind it to cpu 0.
+		 * In case alloc_cpumask_var() fails, bind it to cpu 0.
 		 */
 		channel->numa_node = 0;
 		channel->target_cpu = 0;
@@ -641,7 +643,7 @@ static void init_vp_index(struct vmbus_channel *channel, u16 dev_type)
 		cpumask_clear(alloced_mask);
 	}
 
-	cpumask_xor(&available_mask, alloced_mask,
+	cpumask_xor(available_mask, alloced_mask,
 		    cpumask_of_node(primary->numa_node));
 
 	cur_cpu = -1;
@@ -659,10 +661,10 @@ static void init_vp_index(struct vmbus_channel *channel, u16 dev_type)
 	}
 
 	while (true) {
-		cur_cpu = cpumask_next(cur_cpu, &available_mask);
+		cur_cpu = cpumask_next(cur_cpu, available_mask);
 		if (cur_cpu >= nr_cpu_ids) {
 			cur_cpu = -1;
-			cpumask_copy(&available_mask,
+			cpumask_copy(available_mask,
 				     cpumask_of_node(primary->numa_node));
 			continue;
 		}
@@ -692,6 +694,8 @@ static void init_vp_index(struct vmbus_channel *channel, u16 dev_type)
 
 	channel->target_cpu = cur_cpu;
 	channel->target_vp = hv_cpu_number_to_vp_number(cur_cpu);
+
+	free_cpumask_var(available_mask);
 }
 
 static void vmbus_wait_for_unload(void)