In the error path for nvme_init_subsystem(), nvme_put_subsystem()
will call device_put(), but it will get called again after the
mutex_unlock().

The device_put() only needs to be called if device_add() fails.

This bug caused a KASAN use-after-free error when adding and
removing subsytems in a loop:

  BUG: KASAN: use-after-free in device_del+0x8d9/0x9a0
  Read of size 8 at addr ffff8883cdaf7120 by task multipathd/329

  CPU: 0 PID: 329 Comm: multipathd Not tainted 5.2.0-rc6-vmlocalyes-00019-g70a2b39005fd-dirty #314
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
  Call Trace:
   dump_stack+0x7b/0xb5
   print_address_description+0x6f/0x280
   ? device_del+0x8d9/0x9a0
   __kasan_report+0x148/0x199
   ? device_del+0x8d9/0x9a0
   ? class_release+0x100/0x130
   ? device_del+0x8d9/0x9a0
   kasan_report+0x12/0x20
   __asan_report_load8_noabort+0x14/0x20
   device_del+0x8d9/0x9a0
   ? device_platform_notify+0x70/0x70
   nvme_destroy_subsystem+0xf9/0x150
   nvme_free_ctrl+0x280/0x3a0
   device_release+0x72/0x1d0
   kobject_put+0x144/0x410
   put_device+0x13/0x20
   nvme_free_ns+0xc4/0x100
   nvme_release+0xb3/0xe0
   __blkdev_put+0x549/0x6e0
   ? kasan_check_write+0x14/0x20
   ? bd_set_size+0xb0/0xb0
   ? kasan_check_write+0x14/0x20
   ? mutex_lock+0x8f/0xe0
   ? __mutex_lock_slowpath+0x20/0x20
   ? locks_remove_file+0x239/0x370
   blkdev_put+0x72/0x2c0
   blkdev_close+0x8d/0xd0
   __fput+0x256/0x770
   ? _raw_read_lock_irq+0x40/0x40
   ____fput+0xe/0x10
   task_work_run+0x10c/0x180
   ? filp_close+0xf7/0x140
   exit_to_usermode_loop+0x151/0x170
   do_syscall_64+0x240/0x2e0
   ? prepare_exit_to_usermode+0xd5/0x190
   entry_SYSCALL_64_after_hwframe+0x44/0xa9
  RIP: 0033:0x7f5a79af05d7
  Code: 00 00 0f 05 48 3d 00 f0 ff ff 77 3f c3 66 0f 1f 44 00 00 53 89 fb 48 83 ec 10 e8 c4 fb ff ff 89 df 89 c2 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 2b 89 d7 89 44 24 0c e8 06 fc ff ff 8b 44 24
  RSP: 002b:00007f5a7799c810 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
  RAX: 0000000000000000 RBX: 0000000000000008 RCX: 00007f5a79af05d7
  RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000008
  RBP: 00007f5a58000f98 R08: 0000000000000002 R09: 00007f5a7935ee80
  R10: 0000000000000000 R11: 0000000000000293 R12: 000055e432447240
  R13: 0000000000000000 R14: 0000000000000001 R15: 000055e4324a9cf0

  Allocated by task 1236:
   save_stack+0x21/0x80
   __kasan_kmalloc.constprop.6+0xab/0xe0
   kasan_kmalloc+0x9/0x10
   kmem_cache_alloc_trace+0x102/0x210
   nvme_init_identify+0x13c3/0x3820
   nvme_loop_configure_admin_queue+0x4fa/0x5e0
   nvme_loop_create_ctrl+0x469/0xf40
   nvmf_dev_write+0x19a3/0x21ab
   __vfs_write+0x66/0x120
   vfs_write+0x154/0x490
   ksys_write+0x104/0x240
   __x64_sys_write+0x73/0xb0
   do_syscall_64+0xa5/0x2e0
   entry_SYSCALL_64_after_hwframe+0x44/0xa9

  Freed by task 329:
   save_stack+0x21/0x80
   __kasan_slab_free+0x129/0x190
   kasan_slab_free+0xe/0x10
   kfree+0xa7/0x200
   nvme_release_subsystem+0x49/0x60
   device_release+0x72/0x1d0
   kobject_put+0x144/0x410
   put_device+0x13/0x20
   klist_class_dev_put+0x31/0x40
   klist_put+0x8f/0xf0
   klist_del+0xe/0x10
   device_del+0x3a7/0x9a0
   nvme_destroy_subsystem+0xf9/0x150
   nvme_free_ctrl+0x280/0x3a0
   device_release+0x72/0x1d0
   kobject_put+0x144/0x410
   put_device+0x13/0x20
   nvme_free_ns+0xc4/0x100
   nvme_release+0xb3/0xe0
   __blkdev_put+0x549/0x6e0
   blkdev_put+0x72/0x2c0
   blkdev_close+0x8d/0xd0
   __fput+0x256/0x770
   ____fput+0xe/0x10
   task_work_run+0x10c/0x180
   exit_to_usermode_loop+0x151/0x170
   do_syscall_64+0x240/0x2e0
   entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: 32fd90c4 ("nvme: change locking for the per-subsystem controller list")
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by : Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>