From: Michael Kelley <mikelley@xxxxxxxxxxxxx>
[ Upstream commit 382e06d11e075a40b4094b6ef809f8d4bcc7ab2a ]
When the number of sub-channels offered by Hyper-V is >= the number of CPUs
in the VM, calculate the correct number of sub-channels. The current code
produces one too many.
This scenario arises only when the number of CPUs is artificially
restricted (for example, with maxcpus=<n> on the kernel boot line), because
Hyper-V normally offers a sub-channel count < number of CPUs. While the
current code doesn't break, the extra sub-channel is unbalanced across the
CPUs (for example, a total of 5 channels on a VM with 4 CPUs).
Signed-off-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Reviewed-by: Long Li <longli@xxxxxxxxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/scsi/storvsc_drv.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index f03dc03a42c3..0c2ba075bc71 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -664,13 +664,22 @@ static void handle_sc_creation(struct vmbus_channel *new_sc)
static void handle_multichannel_storage(struct hv_device *device, int max_chns)
{
struct storvsc_device *stor_device;
- int num_cpus = num_online_cpus();
int num_sc;
struct storvsc_cmd_request *request;
struct vstor_packet *vstor_packet;
int ret, t;
- num_sc = ((max_chns > num_cpus) ? num_cpus : max_chns);
+ /*
+ * If the number of CPUs is artificially restricted, such as
+ * with maxcpus=1 on the kernel boot line, Hyper-V could offer
+ * sub-channels >= the number of CPUs. These sub-channels
+ * should not be created. The primary channel is already created
+ * and assigned to one CPU, so check against # CPUs - 1.
+ */
+ num_sc = min((int)(num_online_cpus() - 1), max_chns);
+ if (!num_sc)
+ return;
+
stor_device = get_out_stor_device(device);
if (!stor_device)
return;
--
2.19.1
