[PATCH] block: Fix kernel panic occurs while creating second raid disk

[Sreekanth Reddy <sreekanth.reddy@broadcom.com>]

Observing below kernel panic while creating second raid disk
on LSI SAS3008 HBA card.

[  +0.000055] ------------[ cut here ]------------
[  +0.000007] WARNING: CPU: 2 PID: 281 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x62/0x80
[  +0.000002] sysfs: cannot create duplicate filename '/devices/virtual/bdi/8:32'
[  +0.000001] Modules linked in: mptctl mptbase xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat  nf_conntrack tun bridge stp llc ebtable_filter ebtables ip6table_filter ip6_tables intel_rapl sb_edac edac_core x86_pkg_temp_pclmul joydev ghash_clmulni_intel iTCO_wdt ipmi_ssif mei_me pcspkr mei iTCO_vendor_support ipmi_si i2c_i801 lpc_ich mfd_corema acpi_pad wmi acpi_power_meter nfsd auth_rpcgss nfs_acl lockd grace binfmt_misc sunrpc xfs libcrc32c ast i2c_algo_bit drm_kore raid_class nvme_core scsi_transport_sas dca
[  +0.000067] CPU: 2 PID: 281 Comm: kworker/u49:5 Not tainted 4.9.0-rc2 #1
[  +0.000002] Hardware name: Supermicro SYS-2028U-TNRT+/X10DRU-i+, BIOS 1.1 07/22/2015
[  +0.000005] Workqueue: events_unbound async_run_entry_fn
[  +0.000004] Call Trace:
[  +0.000009]  [<ffffffff813ca51e>] dump_stack+0x63/0x85
[  +0.000005]  [<ffffffff810a5bfb>] __warn+0xcb/0xf0
[  +0.000004]  [<ffffffff810a5c7f>] warn_slowpath_fmt+0x5f/0x80
[  +0.000006]  [<ffffffff812bf17f>] ? kernfs_path_from_node+0x4f/0x60
[  +0.000002]  [<ffffffff812c2942>] sysfs_warn_dup+0x62/0x80
[  +0.000002]  [<ffffffff812c2a27>] sysfs_create_dir_ns+0x77/0x90
[  +0.000004]  [<ffffffff813ccef9>] kobject_add_internal+0x99/0x330
[  +0.000003]  [<ffffffff813d6efb>] ? vsnprintf+0x35b/0x4c0
[  +0.000003]  [<ffffffff813cd6f5>] kobject_add+0x75/0xd0
[  +0.000006]  [<ffffffff81514e43>] ? device_private_init+0x23/0x70
[  +0.000007]  [<ffffffff817cb652>] ? mutex_lock+0x12/0x30
[  +0.000003]  [<ffffffff81514fa9>] device_add+0x119/0x670
[  +0.000004]  [<ffffffff815156f0>] device_create_groups_vargs+0xe0/0xf0
[  +0.000003]  [<ffffffff8151571c>] device_create_vargs+0x1c/0x20
[  +0.000006]  [<ffffffff811d712c>] bdi_register+0x8c/0x180
[  +0.000003]  [<ffffffff811d7506>] bdi_register_owner+0x36/0x60
[  +0.000006]  [<ffffffff813ad778>] device_add_disk+0x168/0x480
[  +0.000005]  [<ffffffff81524891>] ? update_autosuspend+0x51/0x60
[  +0.000005]  [<ffffffff81557770>] sd_probe_async+0x110/0x1c0
[  +0.000002]  [<ffffffff810c8a49>] async_run_entry_fn+0x39/0x140
[  +0.000003]  [<ffffffff810bfa5f>] process_one_work+0x15f/0x430
[  +0.000002]  [<ffffffff810bfd7e>] worker_thread+0x4e/0x490
[  +0.000002]  [<ffffffff810bfd30>] ? process_one_work+0x430/0x430
[  +0.000003]  [<ffffffff810c55a9>] kthread+0xd9/0xf0
[  +0.000003]  [<ffffffff810c54d0>] ? kthread_park+0x60/0x60
[  +0.000003]  [<ffffffff817ce595>] ret_from_fork+0x25/0x30
[  +0.000002] ------------[ cut here ]------------
[  +0.000004] WARNING: CPU: 2 PID: 281 at lib/kobject.c:240 kobject_add_internal+0x2bd/0x330
[  +0.000001] kobject_add_internal failed for 8:32 with -EEXIST, don't try to register things with the same name in the same
[  +0.000001] Modules linked in: mptctl mptbase xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat  nf_conntrack tun bridge stp llc ebtable_filter ebtables ip6table_filter ip6_tables intel_rapl sb_edac edac_core x86_pkg_temp_pclmul joydev ghash_clmulni_intel iTCO_wdt ipmi_ssif mei_me pcspkr mei iTCO_vendor_support ipmi_si i2c_i801 lpc_ich mfd_corema acpi_pad wmi acpi_power_meter nfsd auth_rpcgss nfs_acl lockd grace binfmt_misc sunrpc xfs libcrc32c ast i2c_algo_bit drm_kore raid_class nvme_core scsi_transport_sas dca
[  +0.000043] CPU: 2 PID: 281 Comm: kworker/u49:5 Tainted: G        W       4.9.0-rc2 #1
[  +0.000001] Hardware name: Supermicro SYS-2028U-TNRT+/X10DRU-i+, BIOS 1.1 07/22/2015
[  +0.000002] Workqueue: events_unbound async_run_entry_fn
[  +0.000003] Call Trace:
[  +0.000003]  [<ffffffff813ca51e>] dump_stack+0x63/0x85
[  +0.000003]  [<ffffffff810a5bfb>] __warn+0xcb/0xf0
[  +0.000004]  [<ffffffff810a5c7f>] warn_slowpath_fmt+0x5f/0x80
[  +0.000002]  [<ffffffff812c294a>] ? sysfs_warn_dup+0x6a/0x80
[  +0.000003]  [<ffffffff813cd11d>] kobject_add_internal+0x2bd/0x330
[  +0.000003]  [<ffffffff813d6efb>] ? vsnprintf+0x35b/0x4c0
[  +0.000003]  [<ffffffff813cd6f5>] kobject_add+0x75/0xd0
[  +0.000003]  [<ffffffff81514e43>] ? device_private_init+0x23/0x70
[  +0.000004]  [<ffffffff817cb652>] ? mutex_lock+0x12/0x30
[  +0.000002]  [<ffffffff81514fa9>] device_add+0x119/0x670
[  +0.000004]  [<ffffffff815156f0>] device_create_groups_vargs+0xe0/0xf0
[  +0.000003]  [<ffffffff8151571c>] device_create_vargs+0x1c/0x20
[  +0.000003]  [<ffffffff811d712c>] bdi_register+0x8c/0x180
[  +0.000003]  [<ffffffff811d7506>] bdi_register_owner+0x36/0x60
[  +0.000004]  [<ffffffff813ad778>] device_add_disk+0x168/0x480
[  +0.000003]  [<ffffffff81524891>] ? update_autosuspend+0x51/0x60
[  +0.000002]  [<ffffffff81557770>] sd_probe_async+0x110/0x1c0
[  +0.000002]  [<ffffffff810c8a49>] async_run_entry_fn+0x39/0x140
[  +0.000002]  [<ffffffff810bfa5f>] process_one_work+0x15f/0x430
[  +0.000002]  [<ffffffff810bfd7e>] worker_thread+0x4e/0x490
[  +0.000002]  [<ffffffff810bfd30>] ? process_one_work+0x430/0x430
[  +0.000003]  [<ffffffff810c55a9>] kthread+0xd9/0xf0
[  +0.000003]  [<ffffffff810c54d0>] ? kthread_park+0x60/0x60
[  +0.000003]  [<ffffffff817ce595>] ret_from_fork+0x25/0x30
[  +0.000949] BUG: unable to handle kernel
[  +0.005263] NULL pointer dereference
[  +0.002853] IP: [<ffffffff812c2c64>] sysfs_do_create_link_sd.isra.2+0x34/0xb0
[  +0.008584] PGD 0

[  +0.006115] Oops: 0000 [#1] SMP
[  +0.004531] Modules linked in: mptctl mptbase xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat  nf_conntrack tun bridge stp llc ebtable_filter ebtables ip6table_filter ip6_tables intel_rapl sb_edac edac_core x86_pkg_temp_pclmul joydev ghash_clmulni_intel iTCO_wdt ipmi_ssif mei_me pcspkr mei iTCO_vendor_support ipmi_si i2c_i801 lpc_ich mfd_corema acpi_pad wmi acpi_power_meter nfsd auth_rpcgss nfs_acl lockd grace binfmt_misc sunrpc xfs libcrc32c ast i2c_algo_bit drm_kore raid_class nvme_core scsi_transport_sas dca
[  +0.080566] CPU: 17 PID: 281 Comm: kworker/u49:5 Tainted: G        W       4.9.0-rc2 #1
[  +0.009472] Hardware name: Supermicro SYS-2028U-TNRT+/X10DRU-i+, BIOS 1.1 07/22/2015
[  +0.009169] Workqueue: events_unbound async_run_entry_fn
[  +0.007340] RIP: 0010:[<ffffffff812c2c64>]  [<ffffffff812c2c64>] sysfs_do_create_link_sd.isra.2+0x34/0xb0
[  +0.010294] Call Trace:
[  +0.005269]  [<ffffffff812c2d05>] sysfs_create_link+0x25/0x40
[  +0.008568]  [<ffffffff813ad80c>] device_add_disk+0x1fc/0x480
[  +0.008551]  [<ffffffff81557770>] sd_probe_async+0x110/0x1c0
[  +0.008456]  [<ffffffff810c8a49>] async_run_entry_fn+0x39/0x140
[  +0.010021]  [<ffffffff810bfa5f>] process_one_work+0x15f/0x430
[  +0.009623]  [<ffffffff810bfd7e>] worker_thread+0x4e/0x490
[  +0.007422]  [<ffffffff810bfd30>] ? process_one_work+0x430/0x430
[  +0.008728]  [<ffffffff810c55a9>] kthread+0xd9/0xf0
[  +0.007578]  [<ffffffff810c54d0>] ? kthread_park+0x60/0x60
[  +0.006816]  [<ffffffff817ce595>] ret_from_fork+0x25/0x30
[  +0.006814] Code: 75 48 85 ff 74 70 55 48 89 e5 41 57 41 56 41 55 41 54 49 89 fe 53 48 c7 c7 90 74 01 82 48 89 f3 41 89 cc  c5 ff ff c6 05 15 48 d5
[  +0.022853] RIP  [<ffffffff812c2c64>] sysfs_do_create_link_sd.isra.2+0x34/0xb0
[  +0.008679]  RSP <ffffc90019c3fd10>
[  +0.006129] BUG: unable to handle kernel

While analyzing this issue, I observed that while creating the first raid disk,
we hide first raid disk's PD devices (i.e. device will be their but it won't have
block device entry). But kernel is not removing the entries of this first raid disk's
 PD devices BDI's in /sys/devices/virtual/bdi/ path, still it shows bdi device entries
for these PD eventhough these PD doesn't have a block device names.

e.g.
output of 'ls -l /dev/sd*' after creating first raid disk
[root@dhcp ~]# ls -l /dev/sd*
brw-rw---- 1 root disk 8,   0 Oct 24 17:37 /dev/sda
brw-rw---- 1 root disk 8,   1 Oct 24 17:37 /dev/sda1
brw-rw---- 1 root disk 8,   2 Oct 24 17:37 /dev/sda2
brw-rw---- 1 root disk 8,   3 Oct 24 17:37 /dev/sda3
brw-rw---- 1 root disk 8,  16 Oct 24 17:37 /dev/sdb
brw-rw---- 1 root disk 8,  64 Oct 24 17:37 /dev/sde
brw-rw---- 1 root disk 8,  80 Oct 24 17:37 /dev/sdf
brw-rw---- 1 root disk 8,  96 Oct 24 17:37 /dev/sdg
brw-rw---- 1 root disk 8, 112 Oct 24 17:37 /dev/sdh
brw-rw---- 1 root disk 8, 128 Oct 24 17:37 /dev/sdi
brw-rw---- 1 root disk 8, 144 Oct 24 17:37 /dev/sdj
brw-rw---- 1 root disk 8, 160 Oct 24 17:41 /dev/sdk

outout of 'ls -l /sys/devices/virtual/bdi/'
[root@dhcp-135-24-192-127 ~]# ls -l /sys/devices/virtual/bdi/
total 0
drwxr-xr-x 3 root root 0 Oct 24 17:39 259:0
drwxr-xr-x 3 root root 0 Oct 24 17:39 8:0
drwxr-xr-x 3 root root 0 Oct 24 17:39 8:112
drwxr-xr-x 3 root root 0 Oct 24 17:39 8:128
drwxr-xr-x 3 root root 0 Oct 24 17:39 8:144
drwxr-xr-x 3 root root 0 Oct 24 17:39 8:16
drwxr-xr-x 3 root root 0 Oct 24 17:41 8:160
drwxr-xr-x 3 root root 0 Oct 24 17:39 8:32
drwxr-xr-x 3 root root 0 Oct 24 17:39 8:48
drwxr-xr-x 3 root root 0 Oct 24 17:39 8:64
drwxr-xr-x 3 root root 0 Oct 24 17:39 8:80
drwxr-xr-x 3 root root 0 Oct 24 17:39 8:96

Here we can observe that there are no block devices for
'8:32' & '8:48' bdi entries, which are PD's for raid disk /dev/sdk.

Now while creating a second raid disk, kernel is trying to use
MAJOR:MINOR as 8:32 for second raid disk and we observe
above kernel OOPs.

By calling bdi_unregister() in del_gendisk() function has resolved this
issue.

Signed-off-by: Sreekanth Reddy <Sreekanth.Reddy@broadcom.com>
---
 block/genhd.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/block/genhd.c b/block/genhd.c
index fcd6d4f..b95f2fa 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -658,6 +658,7 @@ void del_gendisk(struct gendisk *disk)
 	disk->flags &= ~GENHD_FL_UP;
 
 	sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi");
+	bdi_unregister(&disk->queue->backing_dev_info);
 	blk_unregister_queue(disk);
 	blk_unregister_region(disk_devt(disk), disk->minors);
 
-- 
2.0.2