linux-kernel - Re: [PATCH] erofs: fix the per-CPU buffer decompression for small output size

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Date:   Wed, 13 Oct 2021 19:51:55 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Yue Hu <zbestahu@...il.com>
Cc:     xiang@...nel.org, chao@...nel.org, linux-erofs@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, huyue2@...ong.com,
        zhangwen@...ong.com, zbestahu@....com
Subject: Re: [PATCH] erofs: fix the per-CPU buffer decompression for small
 output size

Hi Yue,

On Wed, Oct 13, 2021 at 05:29:05PM +0800, Yue Hu wrote:
> From: Yue Hu <huyue2@...ong.com>
> 
> Note that z_erofs_lz4_decompress() will return a positive value if
> decompression succeeds. However, we do not copy_from_pcpubuf() due
> to !ret. Let's fix it.
> 
> Signed-off-by: Yue Hu <huyue2@...ong.com>

Thanks for catching this. This is a valid issue, but it has no real
impact to the current kernels since such pcluster in practice will be
!inplace_io and trigger "if (nrpages_out == 1 && !rq->inplace_io) {"
above for upstream strategies.

Our customized lz4 implementation will return 0 if success instead, so
it has no issue to our previous products as well.

For such cases, how about updating z_erofs_lz4_decompress() to return
0 if success instead rather than outputsize. Since I'll return 0 if
success for LZMA as well.

Thanks,
Gao Xiang