Date:   Thu, 17 Sep 2020 19:34:50 +0000
From:   Nick Terrell <terrelln@...com>
To:     Chao Yu <yuchao0@...wei.com>
CC:     Nick Terrell <nickrterrell@...il.com>,
        "linux-f2fs-devel@...ts.sourceforge.net" 
        <linux-f2fs-devel@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>, Chris Mason <clm@...com>,
        Petr Malat <oss@...at.biz>, Johannes Weiner <jweiner@...com>,
        Niket Agarwal <niketa@...com>, Yann Collet <cyan@...com>
Subject: Re: [PATCH 6/9] f2fs: zstd: Switch to the zstd-1.4.6 API



> On Sep 17, 2020, at 11:00 AM, Nick Terrell <terrelln@...com> wrote:
> 
> 
> 
>> On Sep 16, 2020, at 11:31 PM, Chao Yu <yuchao0@...wei.com> wrote:
>> 
>> Hi Nick,
>> 
>> On 2020/9/17 2:39, Nick Terrell wrote:
>>>> On Sep 15, 2020, at 11:31 PM, Chao Yu <yuchao0@...wei.com> wrote:
>>>> 
>>>> Hi Nick,
>>>> 
>>>> remove not related mailing list.
>>>> 
>>>> On 2020/9/16 11:43, Nick Terrell wrote:
>>>>> From: Nick Terrell <terrelln@...com>
>>>>> Move away from the compatibility wrapper to the zstd-1.4.6 API. This
>>>>> code is more efficient because it uses the single-pass API instead of
>>>>> the streaming API. The streaming API is not necessary because the whole
>>>>> input and output buffers are available. This saves memory because we
>>>>> don't need to allocate a buffer for the window. It is also more
>>>>> efficient because it saves unnecessary memcpy calls.
>>>>> I've had problems testing this code because I see data truncation before
>>>>> and after this patchset. Help testing this patch would be much
>>>>> appreciated.
>>>> 
>>>> Can you please explain more about data truncation? I'm a little confused...
>>>> 
>>>> Do you mean that f2fs doesn't allocate enough memory for zstd compression,
>>>> so that compression is not finished actually, the compressed data is truncated
>>>> at dst buffer?
>>> Hi Chao,
>>> I’ve tested F2FS using a benchmark I adapted from testing BtrFS [0]. It is possible
>>> that the script I’m using is buggy or is exposing an edge case in F2FS. The files
>>> that I copy to F2FS and compress end up truncated with a hole at the end.
>> 
>> Thanks for your explanation. :)
>> 
>>> It is based off of upstream commit ab29a807a7.
>>> E.g. the end of the copied file looks like this, but the original file has non-zero data
>>> In the end. Until the hole at the end the file is correct.
>>> od dickens | tail -n 5
>>>> 46667760 067502 066167 020056 040440 020163 023511 006555 060412
>>>> 46670000 000000 000000 000000 000000 000000 000000 000000 000000
>>>> *
>>>> 46703060 000000 000000 000000 000000 000000 000000 000000
>>>> 46703076
>>> [0] https://gist.github.com/terrelln/7dd2919937dfbdb8e839e4ad11c81db4
>> 
>> Shouldn't we just get sha1 value by flitering sha1sum output?
>> 
>>               asha=`sha1sum $BENCHMARK_DIR/$file |awk {'print $1'}`
>>               bsha=`sha1sum $MP/$i/$file |awk {'print $1'}`
> 
> Probably, but it was just a quick one-off script.

Ah, never mind, you are right.

>> I can't reproduce this issue by using simple data sample, could you share
>> that 'dickens' file or other smaller-sized sample if you have?
> 
> The /tmp/silesia directory in the example is populated with all the files from
> this website. It is a popular data compression benchmark corpus. You can
> click on the “total” link to download a zip archive of all the files.
> 
> http://sun.aei.polsl.pl/~sdeor/index.php?page=silesia
> 
> -Nick

I’ve spent some time minimizing the test case. This script [0] is the minimized
test case that doesn’t require any input files, it builds its own.

Several observations:
* The input file needs to be 7700481 bytes large, smaller files don’t trigger the bug.
* You have to `chattr +c` the file after copying it otherwise the bug doesn’t occur.
* After `chattr +c` you have to unmount and remount the filesystem to trigger the bug.

I’ve reproduced on v5.9-rc5 (856deb866d16e). I’ve also reproduced on my host machine
running 5.8.5-arch1-1.

[0] https://gist.github.com/terrelln/4bba325abdfa3a6f014e9911ac92a185

Best,
Nick

>> Thanks,
>> 
>>> Best,
>>> Nick
>>>> Thanks,
>>>> 
>>>>> Signed-off-by: Nick Terrell <terrelln@...com>
>>>>> ---
>>>>> fs/f2fs/compress.c | 102 +++++++++++++++++----------------------------
>>>>> 1 file changed, 38 insertions(+), 64 deletions(-)
>>>>> diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
>>>>> index e056f3a2b404..b79efce81651 100644
>>>>> --- a/fs/f2fs/compress.c
>>>>> +++ b/fs/f2fs/compress.c
>>>>> @@ -11,7 +11,8 @@
>>>>> #include <linux/backing-dev.h>
>>>>> #include <linux/lzo.h>
>>>>> #include <linux/lz4.h>
>>>>> -#include <linux/zstd_compat.h>
>>>>> +#include <linux/zstd.h>
>>>>> +#include <linux/zstd_errors.h>
>>>>>   #include "f2fs.h"
>>>>> #include "node.h"
>>>>> @@ -298,21 +299,21 @@ static const struct f2fs_compress_ops f2fs_lz4_ops = {
>>>>> static int zstd_init_compress_ctx(struct compress_ctx *cc)
>>>>> {
>>>>> 	ZSTD_parameters params;
>>>>> -	ZSTD_CStream *stream;
>>>>> +	ZSTD_CCtx *ctx;
>>>>> 	void *workspace;
>>>>> 	unsigned int workspace_size;
>>>>>   	params = ZSTD_getParams(F2FS_ZSTD_DEFAULT_CLEVEL, cc->rlen, 0);
>>>>> -	workspace_size = ZSTD_CStreamWorkspaceBound(params.cParams);
>>>>> +	workspace_size = ZSTD_estimateCCtxSize_usingCParams(params.cParams);
>>>>>   	workspace = f2fs_kvmalloc(F2FS_I_SB(cc->inode),
>>>>> 					workspace_size, GFP_NOFS);
>>>>> 	if (!workspace)
>>>>> 		return -ENOMEM;
>>>>> -	stream = ZSTD_initCStream(params, 0, workspace, workspace_size);
>>>>> -	if (!stream) {
>>>>> -		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_initCStream failed\n",
>>>>> +	ctx = ZSTD_initStaticCCtx(workspace, workspace_size);
>>>>> +	if (!ctx) {
>>>>> +		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_inittaticCStream failed\n",
>>>>> 				KERN_ERR, F2FS_I_SB(cc->inode)->sb->s_id,
>>>>> 				__func__);
>>>>> 		kvfree(workspace);
>>>>> @@ -320,7 +321,7 @@ static int zstd_init_compress_ctx(struct compress_ctx *cc)
>>>>> 	}
>>>>>   	cc->private = workspace;
>>>>> -	cc->private2 = stream;
>>>>> +	cc->private2 = ctx;
>>>>>   	cc->clen = cc->rlen - PAGE_SIZE - COMPRESS_HEADER_SIZE;
>>>>> 	return 0;
>>>>> @@ -335,65 +336,48 @@ static void zstd_destroy_compress_ctx(struct compress_ctx *cc)
>>>>>   static int zstd_compress_pages(struct compress_ctx *cc)
>>>>> {
>>>>> -	ZSTD_CStream *stream = cc->private2;
>>>>> -	ZSTD_inBuffer inbuf;
>>>>> -	ZSTD_outBuffer outbuf;
>>>>> -	int src_size = cc->rlen;
>>>>> -	int dst_size = src_size - PAGE_SIZE - COMPRESS_HEADER_SIZE;
>>>>> -	int ret;
>>>>> -
>>>>> -	inbuf.pos = 0;
>>>>> -	inbuf.src = cc->rbuf;
>>>>> -	inbuf.size = src_size;
>>>>> -
>>>>> -	outbuf.pos = 0;
>>>>> -	outbuf.dst = cc->cbuf->cdata;
>>>>> -	outbuf.size = dst_size;
>>>>> -
>>>>> -	ret = ZSTD_compressStream(stream, &outbuf, &inbuf);
>>>>> -	if (ZSTD_isError(ret)) {
>>>>> -		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_compressStream failed, ret: %d\n",
>>>>> -				KERN_ERR, F2FS_I_SB(cc->inode)->sb->s_id,
>>>>> -				__func__, ZSTD_getErrorCode(ret));
>>>>> -		return -EIO;
>>>>> -	}
>>>>> -
>>>>> -	ret = ZSTD_endStream(stream, &outbuf);
>>>>> +	ZSTD_CCtx *ctx = cc->private2;
>>>>> +	const size_t src_size = cc->rlen;
>>>>> +	const size_t dst_size = src_size - PAGE_SIZE - COMPRESS_HEADER_SIZE;
>>>>> +	ZSTD_parameters params = ZSTD_getParams(F2FS_ZSTD_DEFAULT_CLEVEL, src_size, 0);
>>>>> +	size_t ret;
>>>>> +
>>>>> +	ret = ZSTD_compress_advanced(
>>>>> +			ctx, cc->cbuf->cdata, dst_size, cc->rbuf, src_size, NULL, 0, params);
>>>>> 	if (ZSTD_isError(ret)) {
>>>>> -		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_endStream returned %d\n",
>>>>> +		/*
>>>>> +		 * there is compressed data remained in intermediate buffer due to
>>>>> +		 * no more space in cbuf.cdata
>>>>> +		 */
>>>>> +		if (ZSTD_getErrorCode(ret) == ZSTD_error_dstSize_tooSmall)
>>>>> +			return -EAGAIN;
>>>>> +		/* other compression errors return -EIO */
>>>>> +		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_compress_advanced failed, err: %s\n",
>>>>> 				KERN_ERR, F2FS_I_SB(cc->inode)->sb->s_id,
>>>>> -				__func__, ZSTD_getErrorCode(ret));
>>>>> +				__func__, ZSTD_getErrorName(ret));
>>>>> 		return -EIO;
>>>>> 	}
>>>>> -	/*
>>>>> -	 * there is compressed data remained in intermediate buffer due to
>>>>> -	 * no more space in cbuf.cdata
>>>>> -	 */
>>>>> -	if (ret)
>>>>> -		return -EAGAIN;
>>>>> -
>>>>> -	cc->clen = outbuf.pos;
>>>>> +	cc->clen = ret;
>>>>> 	return 0;
>>>>> }
>>>>>   static int zstd_init_decompress_ctx(struct decompress_io_ctx *dic)
>>>>> {
>>>>> -	ZSTD_DStream *stream;
>>>>> +	ZSTD_DCtx *ctx;
>>>>> 	void *workspace;
>>>>> 	unsigned int workspace_size;
>>>>> -	workspace_size = ZSTD_DStreamWorkspaceBound(MAX_COMPRESS_WINDOW_SIZE);
>>>>> +	workspace_size = ZSTD_estimateDCtxSize();
>>>>>   	workspace = f2fs_kvmalloc(F2FS_I_SB(dic->inode),
>>>>> 					workspace_size, GFP_NOFS);
>>>>> 	if (!workspace)
>>>>> 		return -ENOMEM;
>>>>> -	stream = ZSTD_initDStream(MAX_COMPRESS_WINDOW_SIZE,
>>>>> -					workspace, workspace_size);
>>>>> -	if (!stream) {
>>>>> -		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_initDStream failed\n",
>>>>> +	ctx = ZSTD_initStaticDCtx(workspace, workspace_size);
>>>>> +	if (!ctx) {
>>>>> +		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_initStaticDCtx failed\n",
>>>>> 				KERN_ERR, F2FS_I_SB(dic->inode)->sb->s_id,
>>>>> 				__func__);
>>>>> 		kvfree(workspace);
>>>>> @@ -401,7 +385,7 @@ static int zstd_init_decompress_ctx(struct decompress_io_ctx *dic)
>>>>> 	}
>>>>>   	dic->private = workspace;
>>>>> -	dic->private2 = stream;
>>>>> +	dic->private2 = ctx;
>>>>>   	return 0;
>>>>> }
>>>>> @@ -415,28 +399,18 @@ static void zstd_destroy_decompress_ctx(struct decompress_io_ctx *dic)
>>>>>   static int zstd_decompress_pages(struct decompress_io_ctx *dic)
>>>>> {
>>>>> -	ZSTD_DStream *stream = dic->private2;
>>>>> -	ZSTD_inBuffer inbuf;
>>>>> -	ZSTD_outBuffer outbuf;
>>>>> -	int ret;
>>>>> -
>>>>> -	inbuf.pos = 0;
>>>>> -	inbuf.src = dic->cbuf->cdata;
>>>>> -	inbuf.size = dic->clen;
>>>>> -
>>>>> -	outbuf.pos = 0;
>>>>> -	outbuf.dst = dic->rbuf;
>>>>> -	outbuf.size = dic->rlen;
>>>>> +	ZSTD_DCtx *ctx = dic->private2;
>>>>> +	size_t ret;
>>>>> -	ret = ZSTD_decompressStream(stream, &outbuf, &inbuf);
>>>>> +	ret = ZSTD_decompressDCtx(ctx, dic->rbuf, dic->rlen, dic->cbuf->cdata, dic->clen);
>>>>> 	if (ZSTD_isError(ret)) {
>>>>> -		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_compressStream failed, ret: %d\n",
>>>>> +		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD_decompressDCtx failed, err: %s\n",
>>>>> 				KERN_ERR, F2FS_I_SB(dic->inode)->sb->s_id,
>>>>> -				__func__, ZSTD_getErrorCode(ret));
>>>>> +				__func__, ZSTD_getErrorName(ret));
>>>>> 		return -EIO;
>>>>> 	}
>>>>> -	if (dic->rlen != outbuf.pos) {
>>>>> +	if (dic->rlen != ret) {
>>>>> 		printk_ratelimited("%sF2FS-fs (%s): %s ZSTD invalid rlen:%zu, "
>>>>> 				"expected:%lu\n", KERN_ERR,
>>>>> 				F2FS_I_SB(dic->inode)->sb->s_id,

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