Date:	Tue, 10 Nov 2015 09:42:36 +0100
From:	Mads Lønsethagen <mads@....no>
To:	Mads Lønsethagen <mads@....no>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: BUG: unable to handle kernel NULL pointer dereference when
 mounting/umounting vfat in 4.3.0, worked in 4.2.4

On 2015-11-06 21:37, Mads Lønsethagen wrote:

> After updating from 4.2.4 to 4.3.0 I cannot seem to list files in my 
> /boot-folder after mounting it, and I get a kernel BUG when I try to 
> umount it.
> 
> exai ~ # mount /⁠boot
> exai ~ # sync
> exai ~ # mount
> [ ... snip ... ]
> /dev/sda1 on /boot type vfat 
> (rw,noatime,fmask=0022,dmask=0022,codepage=865,iocharset=utf8,shortname=mixed,errors=remount-ro)
> tmpfs on /run/user/1000 type tmpfs 
> (rw,nosuid,nodev,relatime,size=808900k,mode=700,uid=1000,gid=1000)
> exai ~ # ls -⁠l /⁠boot
> ls: cannot open directory /⁠boot: No such device or address
> exai ~ # umount /⁠boot/⁠
> Killed
> exai ~ # dmesg | tail -⁠50
> [ 47.959725] cfg80211: (5150000 KHz - 5250000 KHz @ 80000 KHz, 200000 
> KHz AUTO), (N/A, 2000 mBm), (N/A)
> [ 47.959726] cfg80211: (5250000 KHz - 5350000 KHz @ 80000 KHz, 200000 
> KHz AUTO), (N/A, 2000 mBm), (0 s)
> [ 47.959727] cfg80211: (5470000 KHz - 5725000 KHz @ 160000 KHz), (N/A, 
> 2698 mBm), (0 s)
> [ 47.959728] cfg80211: (57000000 KHz - 66000000 KHz @ 2160000 KHz), 
> (N/A, 4000 mBm), (N/A)
> [ 101.965931] BUG: unable to handle kernel NULL pointer dereference at 
> 0000000000000028
> [ 101.966053] IP: [<ffffffff8110219e>] 
> truncate_inode_pages_range+0x1e/0x6a0
> [ 101.966152] PGD 838e7067 PUD 6c8db067 PMD 0
> [ 101.966222] Oops: 0000 [#1] PREEMPT SMP
> [ 101.966300] Modules linked in: iwlmvm iwlwifi vfat fat uvcvideo 
> videobuf2_vmalloc videobuf2_memops videobuf2_core v4l2_common videodev 
> x86_pkg_temp_thermal coretemp kvm_intel kvm microcode i2c_i801 iTCO_wdt 
> xhci_pci xhci_hcd ideapad_laptop sparse_keymap int3403_thermal 
> int3402_thermal processor_thermal_device int340x_thermal_zone 
> intel_soc_dts_iosf int3400_thermal iosf_mbi acpi_thermal_rel 
> intel_smartconnect efivarfs
> [ 101.967059] CPU: 0 PID: 1311 Comm: umount Not tainted 4.3.0-⁠gentoo 
> #1
> [ 101.967151] Hardware name: LENOVO 20266/Yoga2, BIOS 76CN42WW 
> 03/02/2015
> [ 101.967206] task: ffff880087a23000 ti: ffff88006c92c000 task.ti: 
> ffff88006c92c000
> [ 101.967269] RIP: 0010:[<ffffffff8110219e>] [<ffffffff8110219e>] 
> truncate_inode_pages_range+0x1e/0x6a0
> [ 101.967354] RSP: 0018:ffff88006c92fcd0 EFLAGS: 00010282
> [ 101.967395] RAX: 0000000000000000 RBX: ffffffffffffffff RCX: 
> 9e37fffffffc0001
> [ 101.967453] RDX: ffffffffffffffff RSI: 0000000000000000 RDI: 
> ffff88008897c770
> [ 101.967512] RBP: 0000000000000000 R08: 0000000000000000 R09: 
> 0000000000000000
> [ 101.967571] R10: ffff88008897c718 R11: 0000000000000000 R12: 
> ffffffffa03468c0
> [ 101.967630] R13: ffff88006c930000 R14: ffff8802532bd438 R15: 
> ffff88008897c690
> [ 101.967689] FS: 00007fabc7f61780(0000) GS:ffff88025f200000(0000) 
> knlGS:0000000000000000
> [ 101.967757] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 101.967802] CR2: 0000000000000028 CR3: 000000006c8df000 CR4: 
> 00000000001406f0
> [ 101.967880] Stack:
> [ 101.967897] ffff88008897c770 0000000000000000 ffff880087a23000 
> 0000000000000000
> [ 101.967966] ffffffff81100678 0000000000000000 ffffffff810fefd6 
> ffff88006c92fe58
> [ 101.968034] 00ffffff00000000 00000002900e19c0 ffffffff810fd640 
> ffff8802540b8248
> [ 101.968102] Call Trace:
> [ 101.968117] [<ffffffff81100678>] ? pagevec_lookup_tag+0x18/⁠0x20
> [ 101.968167] [<ffffffff810fefd6>] ? write_cache_pages+0xe6/⁠0x390
> [ 101.968215] [<ffffffff810fd640>] ? domain_dirty_limits+0xe0/⁠0xe0
> [ 101.968266] [<ffffffff81088273>] ? finish_task_switch+0x53/⁠0x180
> [ 101.968316] [<ffffffff810f54f6>] ? find_get_pages_tag+0x126/⁠0x160
> [ 101.968366] [<ffffffff8116bc02>] ? 
> __inode_wait_for_writeback+0x62/0xb0
> [ 101.968422] [<ffffffff8109c420>] ? autoremove_wake_function+0x30/0x30
> [ 101.968478] [<ffffffffa03435a0>] ? fat_evict_inode+0x10/⁠0x50 [fat]
> [ 101.968530] [<ffffffff8115ffa3>] ? evict+0xb3/⁠0x180
> [ 101.968567] [<ffffffff8116009d>] ? dispose_list+0x2d/⁠0x40
> [ 101.968611] [<ffffffff81160e3a>] ? evict_inodes+0x13a/⁠0x150
> [ 101.968656] [<ffffffff81148e15>] ? generic_shutdown_super+0x35/⁠0xe0
> [ 101.968707] [<ffffffff8114914c>] ? kill_block_super+0x1c/⁠0x60
> [ 101.968754] [<ffffffff81149264>] ? deactivate_locked_super+0x34/⁠0x60
> [ 101.968806] [<ffffffff81163db6>] ? cleanup_mnt+0x36/⁠0x80
> [ 101.968860] [<ffffffff81082a7f>] ? task_work_run+0x6f/⁠0x90
> [ 101.968917] [<ffffffff810013f5>] ? prepare_exit_to_usermode+0x95/0xd0
> [ 101.968971] [<ffffffff8175066f>] ? int_ret_from_sys_call+0x25/⁠0x8f
> [ 101.969021] Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 41 57 41 56 
> 41 55 41 54 55 48 89 f5 53 48 89 d3 48 81 ec 10 01 00 00 48 8b 07 48 89 
> 3c 24 <48> 8b 40 28 8b 80 08 04 00 00 85 c0 78 05 e8 cf 19 04 00 48 8b
> [ 101.969295] RIP [<ffffffff8110219e>] 
> truncate_inode_pages_range+0x1e/0x6a0
> [ 101.969355] RSP <ffff88006c92fcd0>
> [ 101.969377] CR2: 0000000000000028
> [ 101.990401] -⁠-⁠-⁠[ end trace a5cb453620b7ad23 ]-⁠-⁠-⁠
> exai ~ #
> 

Fortunately, I'm not able to reproduce this. I think the problem stemmed 
from doing a small change in menuconfig and then forgetting to copy out 
the new bzImage to /boot but having the new modules installed. Sorry for 
the noise.

- Mads
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