linux-kernel - Re: [PATCH linux next] taskstats: fix struct taskstats breaks backward compatibility since version 15

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Message-Id: <20250512180857.59e7836290cb72dad9f3b5d3@linux-foundation.org>
Date: Mon, 12 May 2025 18:08:57 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: <jiang.kun2@....com.cn>
Cc: <bbonev@...uan.org>, <linux-kernel@...r.kernel.org>,
 <bsingharora@...il.com>, <yang.yang29@....com.cn>, <wang.yaxin@....com.cn>,
 <xu.xin16@....com.cn>
Subject: Re: [PATCH linux next] taskstats: fix struct taskstats breaks
 backward  compatibility since version 15

On Sat, 10 May 2025 15:54:13 +0800 (CST) <jiang.kun2@....com.cn> wrote:

> Problem
> ========
> commit 658eb5ab916d ("delayacct: add delay max to record
>  delay peak") - adding more fields
> commit f65c64f311ee ("delayacct: add delay min to record
>  delay peak") - adding more fields
> commit b016d0873777 ("taskstats: modify taskstats version")
>  - version bump to 15
> 
> Since version 15 (TASKSTATS_VERSION=15) the new layout of the
> structure adds fields in the middle of the structure, rendering
> all old software incompatible with newer kernels and software
> compiled against the new kernel headers incompatible with older
> kernels.
> 
> Solution
> =========
> move delay max and delay min to the end of taskstat, and bump
> the version to 16 after the change

Ah, there it it, thanks.

I'll add cc:stable to request a backport.  I'll also add

Fixes: 658eb5ab916d ("delayacct: add delay max to record delay peak")
Fixes: f65c64f311ee ("delayacct: add delay min to record delay peak")

which is odd, but gets the point across.  

The patch won't exactly apply to those kernels because the version
increment came later.  But I think that will be OK - the patch is
applicable to the v6.14 kernel.