Received-SPF: pass (google.com: domain of linux-kernel+bounces-202767-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
Date: Wed, 5 Jun 2024 16:17:33 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org, Andy Lutomirski <luto@amacapital.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dave Hansen <dave@sr71.net>, Peter Zijlstra <peterz@infradead.org>,
	Borislav Petkov <bp@alien8.de>, "H . Peter Anvin" <hpa@zytor.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Uros Bizjak <ubizjak@gmail.com>
Subject: Re: [PATCH 3/3] x86/fpu: Remove init_task FPU state dependencies,
 add debugging warning
Message-ID: <20240605141733.GC25006@redhat.com>
References: <20240605083557.2051480-1-mingo@kernel.org>
 <20240605083557.2051480-4-mingo@kernel.org>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240605083557.2051480-4-mingo@kernel.org>
User-Agent: Mutt/1.5.24 (2015-08-30)

On 06/05, Ingo Molnar wrote:
>
> But the init task isn't supposed to be using the FPU in any case,

Afaics, the same is true for any PF_KTHREAD/USER_WORKER thread?

> +#ifdef CONFIG_X86_DEBUG_FPU
> +struct fpu *x86_task_fpu(struct task_struct *task)
> +{
> +	WARN_ON_ONCE(task == &init_task);
> +
> +	return (void *)task + sizeof(*task);
> +}

So perhaps WARN_ON_ONCE(task->flags & PF_KTHREAD) makes more sense?

Although in this case fpu_clone() can't use x86_task_fpu(dst) as I tried
to suggest in reply to 2/3.


This is offtopic right now, but I am wondering if it makes any sense to
make arch_task_struct_size depend on PF_KTHREAD... I mean, create another
task_struct_kthread_cachep used by alloc_task_struct_node() if PF_KTHREAD.

Oleg.