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Date: Wed, 5 Jun 2024 18:26:11 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>, 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>,
	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: <20240605162610.GF25006@redhat.com>
References: <20240605083557.2051480-1-mingo@kernel.org>
 <20240605083557.2051480-4-mingo@kernel.org>
 <20240605141733.GC25006@redhat.com>
 <CAHk-=wi4773Ls82kqVbPmM1deghS2NXkHNCCzWPc270kcByXPA@mail.gmail.com>
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User-Agent: Mutt/1.5.24 (2015-08-30)

On 06/05, Linus Torvalds wrote:
>
> On Wed, 5 Jun 2024 at 07:19, Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > 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?
>
> I don't think so. We have various users of kernel_fpu_begin()/end()
> that are very much about things like crypto and RAID xor memory copies
> etc that will be used by kernel worker threads.

Yes, but kernel_fpu_begin() never does save_fpregs_to_fpstate() if
current->flags & PF_KTHREAD ?

Oleg.