Manual driver binding and unbinding broken for SCSI

[Omar Sandoval <osandov@osandov.com>]

Hi, everyone,

As per $SUBJECT, I can cause a crash on v4.10-rc8, Jens' block/for-next,
and Jan's bdi branch [1] by doing this:

# lsscsi
[0:0:0:0]    disk    QEMU     QEMU HARDDISK    2.5+  /dev/sda
# echo 0:0:0:0 > /sys/bus/scsi/drivers/sd/unbind
# echo 0:0:0:0 > /sys/bus/scsi/drivers/sd/bind

The resulting trace looks like this:

[   19.347924] kobject (ffff8800791ea0b8): tried to init an initialized object, something is seriously wrong.
[   19.349781] CPU: 1 PID: 84 Comm: kworker/u8:1 Not tainted 4.10.0-rc7-00210-g53f39eeaa263 #34
[   19.350686] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.1-20161122_114906-anatol 04/01/2014
[   19.350920] Workqueue: events_unbound async_run_entry_fn
[   19.350920] Call Trace:
[   19.350920]  dump_stack+0x63/0x83
[   19.350920]  kobject_init+0x77/0x90
[   19.350920]  blk_mq_register_dev+0x40/0x130
[   19.350920]  blk_register_queue+0xb6/0x190
[   19.350920]  device_add_disk+0x1ec/0x4b0
[   19.350920]  sd_probe_async+0x10d/0x1c0 [sd_mod]
[   19.350920]  async_run_entry_fn+0x48/0x150
[   19.350920]  process_one_work+0x1d0/0x480
[   19.350920]  worker_thread+0x48/0x4e0
[   19.350920]  kthread+0x101/0x140
[   19.350920]  ? process_one_work+0x480/0x480
[   19.350920]  ? kthread_create_on_node+0x60/0x60
[   19.350920]  ret_from_fork+0x2c/0x40

Additionally, on v4.10-rc8, but not on block/for-next or Jan's branch,
doing this:

# echo 0:0:0:0 > /sys/bus/scsi/drivers/sd/unbind
# modprobe scsi_debug

Causes this trace:

[   18.876096] ------------[ cut here ]------------
[   18.877057] WARNING: CPU: 1 PID: 90 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x62/0x80
[   18.878270] sysfs: cannot create duplicate filename '/devices/virtual/bdi/8:0'
[   18.879435] Modules linked in: scsi_debug btrfs xor raid6_pq sd_mod virtio_scsi scsi_mod nvme nvme_core virtio_net
[   18.881118] CPU: 1 PID: 90 Comm: kworker/u8:2 Not tainted 4.10.0-rc8 #34
[   18.882114] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.1-20161122_114906-anatol 04/01/2014
[   18.883872] Workqueue: events_unbound async_run_entry_fn
[   18.884408] Call Trace:
[   18.884408]  dump_stack+0x63/0x83
[   18.884408]  __warn+0xcb/0xf0
[   18.884408]  warn_slowpath_fmt+0x5f/0x80
[   18.884408]  ? kernfs_path_from_node+0x4f/0x60
[   18.884408]  sysfs_warn_dup+0x62/0x80
[   18.884408]  sysfs_create_dir_ns+0x77/0x90
[   18.884408]  kobject_add_internal+0xbe/0x350
[   18.884408]  kobject_add+0x75/0xd0
[   18.884408]  device_add+0x121/0x680
[   18.884408]  device_create_groups_vargs+0xe0/0xf0
[   18.884408]  device_create_vargs+0x1c/0x20
[   18.884408]  bdi_register+0x90/0x1b0
[   18.884408]  ? sd_revalidate_disk+0x34a/0x1d00 [sd_mod]
[   18.884408]  bdi_register_owner+0x36/0x60
[   18.884408]  device_add_disk+0x165/0x4a0
[   18.884408]  ? update_autosuspend+0x51/0x60
[   18.884408]  ? __pm_runtime_use_autosuspend+0x5c/0x70
[   18.884408]  sd_probe_async+0x10d/0x1c0 [sd_mod]
[   18.884408]  async_run_entry_fn+0x4a/0x170
[   18.884408]  process_one_work+0x165/0x430
[   18.884408]  worker_thread+0x4e/0x490
[   18.884408]  kthread+0x101/0x140
[   18.884408]  ? process_one_work+0x430/0x430
[   18.884408]  ? kthread_create_on_node+0x60/0x60
[   18.884408]  ret_from_fork+0x2c/0x40
[   18.913090] ---[ end trace f43b051485c2a749 ]---

On all three kernels, it looks like the bdi sysfs entry hangs around
after the block device has already been removed:

┌[root@silver ~]
└# lsblk /dev/sda
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda    8:0    0  16G  0 disk
┌[root@silver ~]
└# ls -al /sys/devices/virtual/bdi
total 0
drwxr-xr-x  6 root root 0 Feb 17 16:19 .
drwxr-xr-x 13 root root 0 Feb 17 16:19 ..
drwxr-xr-x  3 root root 0 Feb 17 16:19 254:0
drwxr-xr-x  3 root root 0 Feb 17 16:19 259:0
drwxr-xr-x  3 root root 0 Feb 17 16:19 8:0
drwxr-xr-x  3 root root 0 Feb 17 16:19 9p-1
┌[root@silver ~]
└# echo 0:0:0:0 > /sys/bus/scsi/drivers/sd/unbind
┌[root@silver ~]
└# ls -al /sys/devices/virtual/bdi
total 0
drwxr-xr-x  6 root root 0 Feb 17 16:19 .
drwxr-xr-x 13 root root 0 Feb 17 16:19 ..
drwxr-xr-x  3 root root 0 Feb 17 16:19 254:0
drwxr-xr-x  3 root root 0 Feb 17 16:19 259:0
drwxr-xr-x  3 root root 0 Feb 17 16:19 8:0
drwxr-xr-x  3 root root 0 Feb 17 16:19 9p-1
┌[root@silver ~]
└# lsblk /dev/sda
lsblk: /dev/sda: not a block device

Any ideas here?

1: https://git.kernel.org/cgit/linux/kernel/git/jack/linux-fs.git/tree/?h=bdi