[PATCH 3.16 279/328] Drivers: hv: vmbus: Use get/put_cpu() in vmbus_connect()

Ben Hutchings
2018-12-09T22:02:48Z

From: Dexuan Cui <decui@microsoft.com>

commit 41e270f6898e7502be9fd6920ee0a108ca259d36 upstream.

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: 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.16:
- smp_processor_id() is only used once here
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/hv/connection.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -68,6 +68,7 @@ static int vmbus_negotiate_version(struc
__u32 version)
{
int ret = 0;
+ unsigned int cur_cpu;
struct vmbus_channel_initiate_contact *msg;
unsigned long flags;

@@ -80,8 +81,11 @@ static int vmbus_negotiate_version(struc
msg->interrupt_page = virt_to_phys(vmbus_connection.int_page);
msg->monitor_page1 = virt_to_phys(vmbus_connection.monitor_pages[0]);
msg->monitor_page2 = virt_to_phys(vmbus_connection.monitor_pages[1]);
- if (version == VERSION_WIN8_1)
- msg->target_vcpu = hv_context.vp_index[smp_processor_id()];
+ if (version == VERSION_WIN8_1) {
+ cur_cpu = get_cpu();
+ msg->target_vcpu = hv_context.vp_index[cur_cpu];
+ put_cpu();
+ }

/*
* Add to list before we send the request since we may