trying to make sense out of kernel oops generated in ext4 subsystem while kernel was experiencing high memory pressure

trying to make sense out of kernel oops generated in ext4 subsystem while kernel was experiencing high memory pressure

[Davis Roman]

Hello,

I got a kernel oops from what appears to be ext4 while my system was
very low on memory. I compiled my kernel with debug symbols and traced
it down to a BUG_ON statement in  fs/ext4/inode.c but I'm having a
hard time trying to figure it out from there.

Any help or insights would be appreciated,

Thank you,

Davis

internal error: Oops - undefined instruction: 0 [#1] PREEMPT SMP ARM
Modules linked in: cdc_mbim cdc_wdm cdc_ncm usbnet mii cdc_acm
xt_multiport nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter
ip6_tables iptable_nat nf_nat_ipv4 ipt_MASQUERADE
nf_nat_masquerade_ipv4 nf_nat nf_conntrack_ipv4 nf_defrag_ipv4
xt_state iptable_filter xt_conntrack nf_conntrack libcrc32c ip_tables
m25p80 gc2145_camera imx_sdma virt_dma ath9k ath9k_common ath9k_hw ath
g_ether usb_f_rndis u_ether libcomposite cryptodev(O) [last unloaded:
at25]
CPU: 0 PID: 33 Comm: kswapd0 Tainted:     4.14.154 #1
Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
task: 8812d140 task.stack: 88af4000
PC is at ext4_writepage+0x564/0x774
LR is at shrink_page_list+0x7e4/0xde0
pc : [<802d7f6c>]    lr : [<801fea9c>]    psr: 000e0013
sp : 88af5ce0  ip : 00000000  fp : 88af5d98
r10: 88af5da8  r9 : 865f2978  r8 : 865f2a54
r7 : 00000000  r6 : 9fedebe0  r5 : 00000001  r4 : 00001000
r3 : 00000000  r2 : 00000125  r1 : 00000000  r0 : 000000ea
Flags: nzcv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 10c53c7d  Table: 147f4059  DAC: 00000051
Process kswapd0 (pid: 33, stack limit = 0x88af4210)
Stack: (0x88af5ce0 to 0x88af6000)
5ce0: 86425750 00064ea6 8642574c 801ec094 88e2c268 88e2c268 88e2c200 ffffffff
5d00: 88af5d98 8042ad38 9fedebe0 88e2c200 00000000 80f03d88 865f2a54 9fedebf4
5d20: 9fedebe0 00000000 88af5f34 865f2a54 00000000 88af5e14 88af5d98 801fea9c
5d40: 00000001 00000003 00000000 00000006 00000000 00000003 88af4000 00000000
5d60: 00000000 0000000f 80f821c0 00000000 00000000 88af5e1c 80fe9f8c 00000000
5d80: 00000000 80e59d74 88af5d40 00000001 00000003 0001ddac 9ff0e574 9ff14ff4
5da0: 9ff08234 9ff0e554 00000020 00000000 00000000 00000000 ffffffff 7fffffff
5dc0: 00000000 00000008 00000000 80f03d88 80e5dccd 80f82e44 88af5f34 00000008
5de0: 00000020 80f82e40 00000000 80f821c0 00000002 801ff7e0 88af5e1c 00000000
5e00: 00000002 80f821c0 00000000 80f821c4 00000020 9ff082d4 9fc41c74 00000000
5e20: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 80f03d88
5e40: 0000173d 00000002 00000152 00000037 88af5ec4 00000020 00000000 80f82e44
5e60: 88af5f34 80200178 88af5ecc 80f821c0 80f03ac0 0000171e 00000000 00000265
5e80: ffffffff ffffffff 51eb851f 80f82e44 000000ee 00000000 88af5f30 88af4000
5ea0: 00000001 88af5ea4 88af5ea4 88af5eac 88af5eac 88af5eb4 88af5eb4 00000000
5ec0: 00000000 00000152 00000295 0000027b 00000000 00000000 00000252 00000375
5ee0: 0000027b 80f03d88 00000000 00000000 00000000 000000ee 00000001 80f82e44
5f00: 00000000 80f821c0 80feb5a0 80200f78 80fe1d40 88af4000 88af5f10 80167694
5f20: ffffe000 80e59da0 80e59d9c 8812d140 00000000 00000265 014000c0 00000000
5f40: 00000000 00000000 00000002 00000000 00000007 000001b8 000000ee 80f03d88
5f60: ffffe000 88282e00 88282d40 00000000 88af4000 80f821c0 80200c54 88282e1c
5f80: 8803de74 8014da78 88af4000 88282d40 8014d954 00000000 00000000 00000000
5fa0: 00000000 00000000 00000000 80108928 00000000 00000000 00000000 00000000
5fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
5fe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000
[<802d7f6c>] (ext4_writepage) from [<801fea9c>] (shrink_page_list+0x7e4/0xde0)
[<801fea9c>] (shrink_page_list) from [<801ff7e0>]
(shrink_inactive_list+0x1c4/0x3dc)
[<801ff7e0>] (shrink_inactive_list) from [<80200178>] (shrink_node+0x44c/0x8b0)
[<80200178>] (shrink_node) from [<80200f78>] (kswapd+0x324/0x668)
[<80200f78>] (kswapd) from [<8014da78>] (kthread+0x124/0x154)
[<8014da78>] (kthread) from [<80108928>] (ret_from_fork+0x14/0x2c)
Code: e519305c e3130b02 0afffefc eaffffc6 (e7f001f2)
---[ end trace 74cf38da7549a08d ]---
Kernel panic - not syncing: Fatal exception





$ arm-poky-linux-gnueabi-addr2line -fe vmlinux 802d7f6c

__ext4_journalled_writepage
/home/davis/linux-rezi/fs/ext4/inode.c:2026

$ bat -r 2019:2029 /home/davis/linux-rezi/fs/ext4/inode.c

2019   │     handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE,
2020   │                     ext4_writepage_trans_blocks(inode));
2021   │     if (IS_ERR(handle)) {
2022   │         ret = PTR_ERR(handle);
2023   │         put_page(page);
2024   │         goto out_no_pagelock;
2025   │     }
2026   │     BUG_ON(!ext4_handle_valid(handle));   <~~~
2027   │
2028   │     lock_page(page);
2029   │     put_page(page);

davis@Precision-7920:~/linux-rezi$ ./scripts/decodecode < /tmp/oops.txt
Code: e519305c e3130b02 0afffefc eaffffc6 (e7f001f2)
All code
========
   0: 5c                    pop    %rsp
   1: 30 19                xor    %bl,(%rcx)
   3: e5 02                in     $0x2,%eax
   5: 0b 13                or     (%rbx),%edx
   7: e3 fc                jrcxz  0x5
   9: fe                    (bad)
   a: ff 0a                decl   (%rdx)
   c: c6                    (bad)
   d: ff                    (bad)
   e: ff                    (bad)
   f: ea                    (bad)
  10:* f2 01 f0              repnz add %esi,%eax <-- trapping instruction
  13: e7                    .byte 0xe7

Code starting with the faulting instruction
===========================================
   0: f2 01 f0              repnz add %esi,%eax
   3: e7                    .byte 0xe7