linux-kernel - [REGRESSION] 4.1-rc6 unloading loop OOPS

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Date:	Thu, 04 Jun 2015 11:11:49 +0200
From:	Stefan Seyfried <stefan.seyfried@...glemail.com>
To:	LKML <linux-kernel@...r.kernel.org>
Subject: [REGRESSION] 4.1-rc6 unloading loop OOPS

Hi all,

I just tried to unload loop to change the max_part parameter on my
freshly booted 4.1-rc6.
This produced this nice Warning, then an OOPS:
[  661.382335] ------------[ cut here ]------------
[  661.382344] WARNING: CPU: 1 PID: 2903 at ../mm/backing-dev.c:372 bdi_unregister+0x32/0x40()
[  661.382346] Modules linked in: ctr ccm fuse xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT xt_tcpudp tun bridge stp llc ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter ip_tables x_tables af_packet bnep bluetooth dm_crypt ecb algif_skcipher af_alg xfs libcrc32c iTCO_wdt iTCO_vendor_support snd_hda_codec_conexant snd_hda_codec_generic snd_hda_intel snd_hda_controller snd_hda_codec snd_hda_core snd_hwdep snd_pcm_oss snd_pcm dm_mod coretemp kvm_intel arc4 kvm snd_seq iwldvm cdc_ether cdc_acm cdc_wdm usbnet mac80211 mii thinkpad_acpi snd_seq_device snd_timer iwlwifi i2c_i801 snd_mixer_oss pcspkr serio_raw cfg80211 lpc_ich snd mfd_core shpchp mei_me mei soundcore rfkill
[  661.382393]  tpm_tis battery ac tpm wmi acpi_cpufreq i915 i2c_algo_bit drm_kms_helper xhci_pci xhci_hcd drm e1000e ptp pps_core video button fan thermal processor sg loop(-)
[  661.382408] CPU: 1 PID: 2903 Comm: rmmod Not tainted 4.1.0-rc6-2.g8f2a4d1-desktop #1
[  661.382410] Hardware name: LENOVO 74665EG/74665EG, BIOS 6DET71WW (3.21 ) 12/13/2011
[  661.382412]  0000000000000000 ffffffff81a4c793 ffffffff8169b34a 0000000000000000
[  661.382415]  ffffffff81067b71 ffff8802307b5400 0000000000000000 0000000000000000
[  661.382418]  00000000ffffffff 0000000000000000 ffffffff8118cdd2 000000000000000e
[  661.382421] Call Trace:
[  661.382434]  [<ffffffff810055bc>] dump_trace+0x8c/0x340
[  661.382438]  [<ffffffff8100596c>] show_stack_log_lvl+0xfc/0x1a0
[  661.382442]  [<ffffffff81007071>] show_stack+0x21/0x50
[  661.382447]  [<ffffffff8169b34a>] dump_stack+0x47/0x67
[  661.382452]  [<ffffffff81067b71>] warn_slowpath_common+0x81/0xb0
[  661.382457]  [<ffffffff8118cdd2>] bdi_unregister+0x32/0x40
[  661.382461]  [<ffffffff8133e040>] del_gendisk+0x110/0x280
[  661.382470]  [<ffffffffa0000351>] loop_remove+0x21/0x50 [loop]
[  661.382476]  [<ffffffffa0000391>] loop_exit_cb+0x11/0x20 [loop]
[  661.382480]  [<ffffffff81359743>] idr_for_each+0xa3/0xf0
[  661.382487]  [<ffffffffa0003516>] loop_exit+0x30/0xb1a [loop]
[  661.382492]  [<ffffffff810ece3c>] SyS_delete_module+0x1ac/0x230
[  661.382497]  [<ffffffff816a1cb2>] system_call_fastpath+0x16/0x75
[  661.382502]  [<00007ff635777f37>] 0x7ff635777f37
[  661.382504] ---[ end trace 7b8e0f39c45cf571 ]---
[  661.449507] BUG: unable to handle kernel NULL pointer dereference at 0000000000000108
[  661.449548] IP: [<ffffffff8135b3ce>] kobject_del+0xe/0x50
[  661.449586] PGD 1d8f2c067 PUD 1d8e7c067 PMD 0 
[  661.449618] Oops: 0000 [#1] PREEMPT SMP 
[  661.449649] Modules linked in: ctr ccm fuse xt_CHECKSUM iptable_mangle ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT xt_tcpudp tun bridge stp llc ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter ip_tables x_tables af_packet bnep bluetooth dm_crypt ecb algif_skcipher af_alg xfs libcrc32c iTCO_wdt iTCO_vendor_support snd_hda_codec_conexant snd_hda_codec_generic snd_hda_intel snd_hda_controller snd_hda_codec snd_hda_core snd_hwdep snd_pcm_oss snd_pcm dm_mod coretemp kvm_intel arc4 kvm snd_seq iwldvm cdc_ether cdc_acm cdc_wdm usbnet mac80211 mii thinkpad_acpi snd_seq_device snd_timer iwlwifi i2c_i801 snd_mixer_oss pcspkr serio_raw cfg80211 lpc_ich snd mfd_core shpchp mei_me mei soundcore rfkill
[  661.449906]  tpm_tis battery ac tpm wmi acpi_cpufreq i915 i2c_algo_bit drm_kms_helper xhci_pci xhci_hcd drm e1000e ptp pps_core video button fan thermal processor sg loop(-)
[  661.449993] CPU: 0 PID: 2903 Comm: rmmod Tainted: G        W       4.1.0-rc6-2.g8f2a4d1-desktop #1
[  661.450025] Hardware name: LENOVO 74665EG/74665EG, BIOS 6DET71WW (3.21 ) 12/13/2011
[  661.450055] task: ffff8802322220d0 ti: ffff8801d8d78000 task.ti: ffff8801d8d78000
[  661.450084] RIP: 0010:[<ffffffff8135b3ce>]  [<ffffffff8135b3ce>] kobject_del+0xe/0x50
[  661.450118] RSP: 0018:ffff8801d8d7bd78  EFLAGS: 00010206
[  661.450146] RAX: ffff88023004ab60 RBX: 00000000000000d8 RCX: 0000000000000001
[  661.450175] RDX: 0000000000000000 RSI: ffff88023078c4d8 RDI: 00000000000000d8
[  661.450203] RBP: ffff88023004f800 R08: ffff88023215a8b8 R09: ffff88023215b0c8
[  661.450217] R10: 0001526900015261 R11: 000000000000000e R12: 0000000000000000
[  661.450217] R13: ffff8802300577e0 R14: ffff88023004f400 R15: ffffffffa0000380
[  661.450217] FS:  00007ff636056700(0000) GS:ffff88023bc00000(0000) knlGS:0000000000000000
[  661.450217] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  661.450217] CR2: 0000000000000108 CR3: 000000023223f000 CR4: 00000000000407f0
[  661.450217] Stack:
[  661.450217]  ffffffffa0000380 0000000000000001 ffff88023004f800 ffffffff8133abed
[  661.450217]  ffff8802319eba80 ffff8802300577e0 ffff88023004f800 ffffffff8133ac61
[  661.450217]  ffff8802300577e0 ffff88023004f400 0000000000000000 00000000ffffffff
[  661.450217] Call Trace:
[  661.450217]  [<ffffffff8133abed>] blk_mq_unregister_hctx.part.0+0x3d/0x60
[  661.450217]  [<ffffffff8133ac61>] blk_mq_unregister_disk+0x51/0xe0
[  661.450217]  [<ffffffff81330a2c>] blk_unregister_queue+0x2c/0x90
[  661.450217]  [<ffffffff8133e048>] del_gendisk+0x118/0x280
[  661.450217]  [<ffffffffa0000351>] loop_remove+0x21/0x50 [loop]
[  661.450217]  [<ffffffffa0000391>] loop_exit_cb+0x11/0x20 [loop]
[  661.450217]  [<ffffffff81359743>] idr_for_each+0xa3/0xf0
[  661.450217]  [<ffffffffa0003516>] loop_exit+0x30/0xb1a [loop]
[  661.450217]  [<ffffffff810ece3c>] SyS_delete_module+0x1ac/0x230
[  661.450217]  [<ffffffff816a1cb2>] system_call_fastpath+0x16/0x75
[  661.450217]  [<00007ff635777f37>] 0x7ff635777f37
[  661.450217] Code: 48 83 c7 18 e9 54 ff ff ff 0f 1f 40 00 5b c3 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 55 53 48 89 fb 48 83 ec 08 48 85 ff 74 2e <48> 8b 6f 30 e8 09 cc ef ff 48 89 ef e8 a1 98 ef ff 80 63 3c fd 
[  661.450217] RIP  [<ffffffff8135b3ce>] kobject_del+0xe/0x50
[  661.450217]  RSP <ffff8801d8d7bd78>
[  661.450217] CR2: 0000000000000108
[  661.466690] ---[ end trace 7b8e0f39c45cf572 ]---

I can reproduce the backtrace after a reboot once (subsequent modprobe/rmmod loop
do not complain anymore), but not the OOPS.

Best regards,

	Stefan
-- 
Stefan Seyfried
Linux Consultant & Developer -- GPG Key: 0x731B665B

B1 Systems GmbH
Osterfeldstraße 7 / 85088 Vohburg / http://www.b1-systems.de
GF: Ralph Dehner / Unternehmenssitz: Vohburg / AG: Ingolstadt,HRB 3537
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