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authorMichael Kelley <mikelley@microsoft.com>2019-04-01 19:10:52 +0300
committerMartin K. Petersen <martin.petersen@oracle.com>2019-04-04 06:30:08 +0300
commit382e06d11e075a40b4094b6ef809f8d4bcc7ab2a (patch)
tree2dd19238b6a478ca22b84758c135e35905c62929 /drivers/scsi/storvsc_drv.c
parent1cb1d2c64e812928fe0a40b8f7e74523d0283dbe (diff)
downloadlinux-382e06d11e075a40b4094b6ef809f8d4bcc7ab2a.tar.xz
scsi: storvsc: Fix calculation of sub-channel count
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@microsoft.com> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com> Reviewed-by: Long Li <longli@microsoft.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Diffstat (limited to 'drivers/scsi/storvsc_drv.c')
-rw-r--r--drivers/scsi/storvsc_drv.c13
1 files changed, 11 insertions, 2 deletions
diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 84380bae20f1..e186743033f4 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -668,13 +668,22 @@ static void handle_multichannel_storage(struct hv_device *device, int max_chns)
{
struct device *dev = &device->device;
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;