linux-kernel - [PATCH 1/3] Drivers: hv: vmbus: avoid infinite loop in init_vp

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Message-Id: <1453137519-20304-2-git-send-email-vkuznets@redhat.com>
Date:	Mon, 18 Jan 2016 18:18:37 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>
Cc:	Haiyang Zhang <haiyangz@...rosoft.com>,
	devel@...uxdriverproject.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] Drivers: hv: vmbus: avoid infinite loop in init_vp_index()

When we pick a CPU to use for a new subchannel we try find a non-used one
on the appropriate NUMA node, we keep track of them with the
primary->alloced_cpus_in_node mask. Under normal circumstances we don't run
out of available CPUs but it is possible when we we don't initialize some
cpus in Linux, e.g. when we boot with 'nr_cpus=' limitation.

Avoid the infinite loop in init_vp_index() by checking that we still have
non-used CPUs in the alloced_cpus_in_node mask and resetting it in case
we don't.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 drivers/hv/channel_mgmt.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 1c1ad47..82c6860 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -469,6 +469,17 @@ static void init_vp_index(struct vmbus_channel *channel, const uuid_le *type_gui
 		    cpumask_of_node(primary->numa_node));
 
 	cur_cpu = -1;
+
+	/*
+	 * Normally Hyper-V host doesn't create more subchannels than there
+	 * are VCPUs on the node but it is possible when not all present VCPUs
+	 * on the node are initialized by guest. Clear the alloced_cpus_in_node
+	 * to start over.
+	 */
+	if (cpumask_equal(&primary->alloced_cpus_in_node,
+			  cpumask_of_node(primary->numa_node)))
+		cpumask_clear(&primary->alloced_cpus_in_node);
+
 	while (true) {
 		cur_cpu = cpumask_next(cur_cpu, &available_mask);
 		if (cur_cpu >= nr_cpu_ids) {
-- 
2.5.0