releases/4.14.117/scsi-storvsc-fix-calculation-of-sub-channel-count.patch

   1 From 25f1f17ea35f080919b29e3993c2c00a7d0e27f9 Mon Sep 17 00:00:00 2001
   2 From: Michael Kelley <mikelley@microsoft.com>
   3 Date: Mon, 1 Apr 2019 16:10:52 +0000
   4 Subject: scsi: storvsc: Fix calculation of sub-channel count
   5
   6 [ Upstream commit 382e06d11e075a40b4094b6ef809f8d4bcc7ab2a ]
   7
   8 When the number of sub-channels offered by Hyper-V is >= the number of CPUs
   9 in the VM, calculate the correct number of sub-channels.  The current code
  10 produces one too many.
  11
  12 This scenario arises only when the number of CPUs is artificially
  13 restricted (for example, with maxcpus=<n> on the kernel boot line), because
  14 Hyper-V normally offers a sub-channel count < number of CPUs.  While the
  15 current code doesn't break, the extra sub-channel is unbalanced across the
  16 CPUs (for example, a total of 5 channels on a VM with 4 CPUs).
  17
  18 Signed-off-by: Michael Kelley <mikelley@microsoft.com>
  19 Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
  20 Reviewed-by: Long Li <longli@microsoft.com>
  21 Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
  22 Signed-off-by: Sasha Levin <sashal@kernel.org>
  23 ---
  24  drivers/scsi/storvsc_drv.c | 13 +++++++++++--
  25  1 file changed, 11 insertions(+), 2 deletions(-)
  26
  27 diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
  28 index beb585ddc07d..5adeb1e4b186 100644
  29 --- a/drivers/scsi/storvsc_drv.c
  30 +++ b/drivers/scsi/storvsc_drv.c
  31 @@ -658,13 +658,22 @@ static void handle_sc_creation(struct vmbus_channel *new_sc)
  32  static void  handle_multichannel_storage(struct hv_device *device, int max_chns)
  33  {
  34         struct storvsc_device *stor_device;
  35 -       int num_cpus = num_online_cpus();
  36         int num_sc;
  37         struct storvsc_cmd_request *request;
  38         struct vstor_packet *vstor_packet;
  39         int ret, t;
  40
  41 -       num_sc = ((max_chns > num_cpus) ? num_cpus : max_chns);
  42 +       /*
  43 +        * If the number of CPUs is artificially restricted, such as
  44 +        * with maxcpus=1 on the kernel boot line, Hyper-V could offer
  45 +        * sub-channels >= the number of CPUs. These sub-channels
  46 +        * should not be created. The primary channel is already created
  47 +        * and assigned to one CPU, so check against # CPUs - 1.
  48 +        */
  49 +       num_sc = min((int)(num_online_cpus() - 1), max_chns);
  50 +       if (!num_sc)
  51 +               return;
  52 +
  53         stor_device = get_out_stor_device(device);
  54         if (!stor_device)
  55                 return;
  56 --
  57 2.20.1
  58