Weird EROFS data corruption

[Juhyung Park]

Hi Gao,

On Mon, Dec 4, 2023 at 12:28 PM Gao Xiang <hsiangkao at linux.alibaba.com> wrote:
>
>
>
> On 2023/12/4 01:32, Juhyung Park wrote:
> > Hi Gao,
>
> ...
>
> >>>
> >>>>
> >>>> What is the difference between these two machines? just different CPU or
> >>>> they have some other difference like different compliers?
> >>>
> >>> I fully and exclusively control both devices, and the setup is almost the same.
> >>> Same Ubuntu version, kernel/compiler version.
> >>>
> >>> But as I said, on my laptop, the issue happens on kernels that someone
> >>> else (Canonical) built, so I don't think it matters.
> >>
> >> The only thing I could say is that the kernel side has optimized
> >> inplace decompression compared to fuse so that it will reuse the
> >> same buffer for decompression but with a safe margin (according to
> >> the current lz4 decompression implementation).  It shouldn't behave
> >> different just due to different CPUs.  Let me find more clues
> >> later, also maybe we should introduce a way for users to turn off
> >> this if needed.
> >
> > Cool :)
> >
> > I'm comfortable changing and building my own custom kernel for this
> > specific laptop. Feel free to ask me to try out some patches.
>
> Thanks, I need to narrow down this issue:
>
> -  First, could you apply the following diff to test if it's still
>     reproducable?
>
> diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
> index 021be5feb1bc..40a306628e1a 100644
> --- a/fs/erofs/decompressor.c
> +++ b/fs/erofs/decompressor.c
> @@ -131,7 +131,7 @@ static void *z_erofs_lz4_handle_overlap(struct z_erofs_lz4_decompress_ctx *ctx,
>
>         if (rq->inplace_io) {
>                 omargin = PAGE_ALIGN(ctx->oend) - ctx->oend;
> -               if (rq->partial_decoding || !may_inplace ||
> +               if (1 || rq->partial_decoding || !may_inplace ||
>                     omargin < LZ4_DECOMPRESS_INPLACE_MARGIN(rq->inputsize))
>                         goto docopy;

Yup, that fixes it.

The hash output is the same for 50 runs.

>
> - Could you share the full message about the output of `lscpu`?

Sure:

Architecture:            x86_64
  CPU op-mode(s):        32-bit, 64-bit
  Address sizes:         39 bits physical, 48 bits virtual
  Byte Order:            Little Endian
CPU(s):                  8
  On-line CPU(s) list:   0-7
Vendor ID:               GenuineIntel
  BIOS Vendor ID:        Intel(R) Corporation
  Model name:            11th Gen Intel(R) Core(TM) i7-1185G7 @ 3.00GHz
    BIOS Model name:     11th Gen Intel(R) Core(TM) i7-1185G7 @ 3.00GHz None CPU
                          @ 3.0GHz
    BIOS CPU family:     198
    CPU family:          6
    Model:               140
    Thread(s) per core:  2
    Core(s) per socket:  4
    Socket(s):           1
    Stepping:            1
    CPU(s) scaling MHz:  60%
    CPU max MHz:         4800.0000
    CPU min MHz:         400.0000
    BogoMIPS:            5990.40
    Flags:               fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mc
                         a cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss
                         ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art
                          arch_perfmon pebs bts rep_good nopl xtopology nonstop_
                         tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq dtes6
                         4 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xt
                         pr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_dead
                         line_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowp
                         refetch cpuid_fault epb cat_l2 cdp_l2 ssbd ibrs ibpb st
                         ibp ibrs_enhanced tpr_shadow flexpriority ept vpid ept_
                         ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid
                          rdt_a avx512f avx512dq rdseed adx smap avx512ifma clfl
                         ushopt clwb intel_pt avx512cd sha_ni avx512bw avx512vl
                         xsaveopt xsavec xgetbv1 xsaves split_lock_detect dtherm
                          ida arat pln pts hwp hwp_notify hwp_act_window hwp_epp
                          hwp_pkg_req vnmi avx512vbmi umip pku ospke avx512_vbmi
                         2 gfni vaes vpclmulqdq avx512_vnni avx512_bitalg tme av
                         x512_vpopcntdq rdpid movdiri movdir64b fsrm avx512_vp2i
                         ntersect md_clear ibt flush_l1d arch_capabilities
Virtualization features:
  Virtualization:        VT-x
Caches (sum of all):
  L1d:                   192 KiB (4 instances)
  L1i:                   128 KiB (4 instances)
  L2:                    5 MiB (4 instances)
  L3:                    12 MiB (1 instance)
NUMA:
  NUMA node(s):          1
  NUMA node0 CPU(s):     0-7
Vulnerabilities:
  Gather data sampling:  Vulnerable
  Itlb multihit:         Not affected
  L1tf:                  Not affected
  Mds:                   Not affected
  Meltdown:              Not affected
  Mmio stale data:       Not affected
  Retbleed:              Not affected
  Spec rstack overflow:  Not affected
  Spec store bypass:     Vulnerable
  Spectre v1:            Vulnerable: __user pointer sanitization and usercopy ba
                         rriers only; no swapgs barriers
  Spectre v2:            Vulnerable, IBPB: disabled, STIBP: disabled, PBRSB-eIBR
                         S: Vulnerable
  Srbds:                 Not affected
  Tsx async abort:       Not affected


>
> Thanks,
> Gao Xiang