Re: Patch 'writeback, cgroup: release dying cgwbs by switching attached inodes' leads to kernel crash

[Boyang Xue <bxue@redhat.com>]

Hi Roman,

On Wed, Jul 14, 2021 at 12:12 PM Roman Gushchin <guro@fb.com> wrote:
>
> On Wed, Jul 14, 2021 at 11:21:12AM +0800, Boyang Xue wrote:
> > Hello,
> >
> > I'm not sure if this is the right place to report this bug, please
> > correct me if I'm wrong.
> >
> > I found kernel-5.14.0-rc1 (built from the Linus tree) crash when it's
> > running xfstests generic/256 on ext4 [1]. Looking at the call trace,
> > it looks like the bug had been introduced by the commit
> >
> > c22d70a162d3 writeback, cgroup: release dying cgwbs by switching attached inodes
> >
> > It only happens on aarch64, not on x86_64, ppc64le and s390x. Testing
> > was performed with the latest xfstests, and the bug can be reproduced
> > on ext{2, 3, 4} with {1k, 2k, 4k} block sizes.
>
> Hello Boyang,
>
> thank you for the report!
>
> Do you know on which line the oops happens?

I was trying to inspect the vmcore with crash utility, but
unfortunately it doesn't work.

```
# crash /usr/lib/debug/lib/modules/5.14.0-0.rc1.15.bx.el9.aarch64/vmlinux vmcore
...
crash: invalid structure member offset: task_struct_state
       FILE: task.c  LINE: 5929  FUNCTION: task_state()

     [/usr/bin/crash] error trace: aaaae238b080 => aaaae238aff0 =>
aaaae23ff4e8 => aaaae23ff440
...
```
Could you suggest other ways to know "the line the oops happens"?

> I'll try to reproduce the problem. Do you mind sharing your .config, kvm options
> and any other meaningful details?

I can't access the VM host, so sorry I can't provide the kvm
configuration for now. Please check the following other info:

xfstests local.config
```
# cat local.config
FSTYP="ext4"
TEST_DIR="/test"
TEST_DEV="/dev/vda3"
SCRATCH_MNT="/scratch"
SCRATCH_DEV="/dev/vda4"
LOGWRITES_MNT="/logwrites"
LOGWRITES_DEV="/dev/vda6"
MKFS_OPTIONS="-b 4096"
MOUNT_OPTIONS="-o rw,relatime,seclabel"
TEST_FS_MOUNT_OPTS="-o rw,relatime,seclabel"
```

# lscpu
Architecture:            aarch64
  CPU op-mode(s):        64-bit
  Byte Order:            Little Endian
CPU(s):                  4
  On-line CPU(s) list:   0-3
Vendor ID:               Cavium
  BIOS Vendor ID:        QEMU
  Model name:            ThunderX2 99xx
    BIOS Model name:     virt-rhel7.6.0
    Model:               1
    Thread(s) per core:  1
    Core(s) per cluster: 4
    Socket(s):           4
    Cluster(s):          1
    Stepping:            0x1
    BogoMIPS:            400.00
    Flags:               fp asimd evtstrm aes pmull sha1 sha2 crc32
atomics cpuid asimdrdm
NUMA:
  NUMA node(s):          1
  NUMA node0 CPU(s):     0-3
Vulnerabilities:
  Itlb multihit:         Not affected
  L1tf:                  Not affected
  Mds:                   Not affected
  Meltdown:              Not affected
  Spec store bypass:     Mitigation; Speculative Store Bypass disabled via prctl
  Spectre v1:            Mitigation; __user pointer sanitization
  Spectre v2:            Mitigation; Branch predictor hardening
  Srbds:                 Not affected
  Tsx async abort:       Not affected

# getconf PAGESIZE
65536

Please let me know if there's other useful info I can provide.

Thanks,
Boyang

>
> Thank you!
>
> Roman
>