linux-kernel - Re: [PATCH v11] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6

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Date: Fri, 1 Mar 2024 07:17:38 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Charlie Jenkins <charlie@...osinc.com>, Guenter Roeck
	<linux@...ck-us.net>, David Laight <David.Laight@...lab.com>, Palmer Dabbelt
	<palmer@...belt.com>, Andrew Morton <akpm@...ux-foundation.org>, Helge Deller
	<deller@....de>, "James E.J. Bottomley"
	<James.Bottomley@...senpartnership.com>, Parisc List
	<linux-parisc@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>, Geert
 Uytterhoeven <geert@...ux-m68k.org>, Russell King <linux@...linux.org.uk>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Palmer
 Dabbelt <palmer@...osinc.com>, Linux ARM
	<linux-arm-kernel@...ts.infradead.org>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>
Subject: Re: [PATCH v11] lib: checksum: Use aligned accesses for ip_fast_csum
 and csum_ipv6_magic tests

+CC netdev ARM Russell

Le 29/02/2024 à 23:46, Charlie Jenkins a écrit :
> The test cases for ip_fast_csum and csum_ipv6_magic were not properly
> aligning the IP header, which were causing failures on architectures
> that do not support misaligned accesses like some ARM platforms. To
> solve this, align the data along (14 + NET_IP_ALIGN) bytes which is the
> standard alignment of an IP header and must be supported by the
> architecture.

In your description, please provide more details on platforms that have 
a problem, what the problem is exactly (Failed calculation, slowliness, 
kernel Oops, panic, ....) on each platform.

And please copy maintainers and lists of platforms your are specifically 
addressing with this change. And as this is network related, netdev list 
should have been copied as well.

I still think that your patch is not the good approach, it looks like 
you are ignoring all the discussion. Below is a quote of what Geert said 
and I fully agree with that:

	IMHO the tests should validate the expected functionality.  If a test
	fails, either functionality is missing or behaves wrong, or the test
	is wrong.

	What is the point of writing tests for a core functionality like network
	checksumming that do not match the expected functionality?

So we all agree that there is something to fix, because today's test 
does odd-address accesses which is unexpected for those functions, but 
2-byte alignments should be supported hence tested by the test. Limiting 
the test to a 16-bytes alignment deeply reduces the usefullness of the test.

Christophe