If the driver is unable to create a subset of IO queues for any reason,
the read/write and polled queue sets will not match the actual allocated
hardware contexts. This leaves gaps in the CPU affinity mappings and
causes the following kernel panic after blk_mq_map_queue_type() returns
a NULL hctx.

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000198
  #PF error: [normal kernel read fault]
  PGD 0 P4D 0
  Oops: 0000 [#1] SMP
  CPU: 64 PID: 1171 Comm: kworker/u259:1 Not tainted 4.20.0+ #241
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-2.fc27 04/01/2014
  Workqueue: nvme-wq nvme_scan_work [nvme_core]
  RIP: 0010:blk_mq_init_allocated_queue+0x2d9/0x440
  RSP: 0018:ffffb1bf0abc3cd0 EFLAGS: 00010286
  RAX: 000000000000001f RBX: ffff8ea744cf0718 RCX: 0000000000000000
  RDX: 0000000000000002 RSI: 000000000000007c RDI: ffffffff9109a820
  RBP: ffff8ea7565f7008 R08: 000000000000001f R09: 000000000000003f
  R10: ffffb1bf0abc3c00 R11: 0000000000000000 R12: 000000000001d008
  R13: ffff8ea7565f7008 R14: 000000000000003f R15: 0000000000000001
  FS:  0000000000000000(0000) GS:ffff8ea757200000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000198 CR3: 0000000013058000 CR4: 00000000000006e0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  Call Trace:
   blk_mq_init_queue+0x35/0x60
   nvme_validate_ns+0xc6/0x7c0 [nvme_core]
   ? nvme_identify_ctrl.isra.56+0x7e/0xc0 [nvme_core]
   nvme_scan_work+0xc8/0x340 [nvme_core]
   ? __wake_up_common+0x6d/0x120
   ? try_to_wake_up+0x55/0x410
   process_one_work+0x1e9/0x3d0
   worker_thread+0x2d/0x3d0
   ? process_one_work+0x3d0/0x3d0
   kthread+0x111/0x130
   ? kthread_park+0x90/0x90
   ret_from_fork+0x1f/0x30
  Modules linked in: nvme nvme_core serio_raw
  CR2: 0000000000000198

Fix by re-running the interrupt vector setup from scratch using a reduced
count that may be successful until the created queues matches the irq
affinity plus polling queue sets.
Signed-off-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>