linux-kernel - Re: [BUG] lib: zram lz4 compression/decompression still broken on big endian

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Date:	Fri, 8 Apr 2016 15:53:30 +0100
From:	Rui Salvaterra <rsalvaterra@...il.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, eunb.song@...sung.com,
	minchan@...nel.org, linux-mm@...ck.org,
	Chanho Min <chanho.min@....com>,
	Kyungsik Lee <kyungsik.lee@....com>
Subject: Re: [BUG] lib: zram lz4 compression/decompression still broken on big endian

2016-04-07 15:07 GMT+01:00 Sergey Senozhatsky <sergey.senozhatsky@...il.com>:
> On (04/07/16 13:33), Rui Salvaterra wrote:
> [..]
>> Hi again, Sergey
>
> Hello,
>
>> Thanks for the patch, I'll test it as soon as possible. I agree with
>> your second option, usually one selects lz4 when (especially
>> decompression) speed is paramount, so it needs all the help it can
>> get.
>
> thanks!
>
>> Speaking of fishy, the 64-bit detection code also looks suspiciously
>> bogus. Some of the identifiers don't even exist anywhere in the kernel
>> (__ppc64__, por example, after grepping all .c and .h files).
>> Shouldn't we instead check for CONFIG_64BIT or BITS_PER_LONG == 64?
>
> definitely a good question. personally, I'd prefer to test for
> CONFIG_64BIT only, looking at this hairy
>
>   /* Detects 64 bits mode */
>   #if (defined(__x86_64__) || defined(__x86_64) || defined(__amd64__) \
>          || defined(__ppc64__) || defined(__LP64__))
>
> and remove/rewrite a bunch of other stuff. but the thing with cleanups
> is that they don't fix anything, while potentially can introduce bugs.
> it's more risky to touch the stable code. /* well, removing those 'ghost'
> identifiers is sort of OK to me */. but that's just my opinion, I'll
> leave it to you and Greg.
>
>         -ss

Hi again, Sergey

I finally was able to test your patch but, as I suspected, it wasn't
enough. However, based on it, I was able to write a (hopefully)
correct one, which I'll send soon (tested on ppc64, with no
regressions on x86_64).

Thanks,

Rui