linux-kernel - Re: [RFC v2 3/3] atomic: Add alignment check to instrumented atomic operations

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Message-Id: <57bca164-4e63-496d-9074-79fd89feb835@app.fastmail.com>
Date: Mon, 15 Sep 2025 13:20:18 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Finn Thain" <fthain@...ux-m68k.org>,
 "Peter Zijlstra" <peterz@...radead.org>
Cc: "Will Deacon" <will@...nel.org>,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "Boqun Feng" <boqun.feng@...il.com>, "Jonathan Corbet" <corbet@....net>,
 "Mark Rutland" <mark.rutland@....com>, linux-kernel@...r.kernel.org,
 Linux-Arch <linux-arch@...r.kernel.org>,
 "Geert Uytterhoeven" <geert@...ux-m68k.org>, linux-m68k@...r.kernel.org
Subject: Re: [RFC v2 3/3] atomic: Add alignment check to instrumented atomic operations

On Mon, Sep 15, 2025, at 12:37, Finn Thain wrote:
> On Mon, 15 Sep 2025, Peter Zijlstra wrote:
>>
>> > When you do atomic operations on atomic_t or atomic64_t, (sizeof(long)
>> > - 1) probably doesn't make much sense. But atomic operations get used on 
>> > scalar types (aside from atomic_t and atomic64_t) that don't have natural 
>> > alignment. Please refer to the other thread about this: 
>> > https://lore.kernel.org/all/ed1e0896-fd85-5101-e136-e4a5a37ca5ff@linux-m68k.org/
>> 
>> Perhaps set ARCH_SLAB_MINALIGN ?
>> 
>
> That's not going to help much. The 850 byte offset of task_works into 
> struct task_struct and the 418 byte offset of exit_state in struct 
> task_struct are already misaligned.

Has there been any progress on building m68k kernels with -mint-align?
IIRC there are only a small number of uapi structures that need
__packed annotations to maintain the existing syscall ABI.

       Arnd