[bug report] IB/usnic: Add Cisco VIC low-level hardware driver

[Dan Carpenter <dan.carpenter@oracle.com>]

[ This is an ancient bug, but the bug is clear to see, but unfortunately
  it's probably less easy to fix.  - dan ]

Hello Upinder Malhi,

The patch e3cf00d0a87f: "IB/usnic: Add Cisco VIC low-level hardware
driver" from Sep 10, 2013, leads to the following static checker
warning:

	fs/kernfs/dir.c:476 kernfs_drain()
	warn: sleeping in atomic context

drivers/infiniband/hw/usnic/usnic_ib_verbs.c
   190          if (usnic_ib_share_vf) {
   191                  /* Try to find resouces on a used vf which is in pd */
   192                  dev_list = usnic_uiom_get_dev_list(pd->umem_pd);
   193                  if (IS_ERR(dev_list))
   194                          return ERR_CAST(dev_list);
   195                  for (i = 0; dev_list[i]; i++) {
   196                          dev = dev_list[i];
   197                          vf = dev_get_drvdata(dev);
   198                          spin_lock(&vf->lock);
                                ^^^^^^^^^^^^^^^^^^^^^
We're holding a spin lock.

   199                          vnic = vf->vnic;
   200                          if (!usnic_vnic_check_room(vnic, res_spec)) {
   201                                  usnic_dbg("Found used vnic %s from %s\n",
   202                                                  dev_name(&us_ibdev->ib_dev.dev),
   203                                                  pci_name(usnic_vnic_get_pdev(
   204                                                                          vnic)));
   205                                  qp_grp = usnic_ib_qp_grp_create(us_ibdev->ufdev,
                                                 ^^^^^^^^^^^^^^^^^^^^^^
The create function calls usnic_ib_sysfs_qpn_add() which does a
kobject_init_and_add().  Unfortunately kobject allocations have many
sleeps inside them so it can't be done while holding a spinlock.

Same thing for the other usnic_ib_qp_grp_create() later on in the same
function.

   206                                                                  vf, pd,
   207                                                                  res_spec,
   208                                                                  trans_spec);
   209  
   210                                  spin_unlock(&vf->lock);
   211                                  goto qp_grp_check;
   212                          }
   213                          spin_unlock(&vf->lock);
   214  
   215                  }
   216                  usnic_uiom_free_dev_list(dev_list);
   217                  dev_list = NULL;
   218          }

regards,
dan carpenter