Re: Weird EROFS data corruption

[Gao Xiang <hsiangkao@linux.alibaba.com>]

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;

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

Thanks,
Gao Xiang