linux-kernel - Re: [PATCH 6/8] x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER

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Message-ID: <Z_omZOmmwpN-iOxn@gmail.com>
Date: Sat, 12 Apr 2025 10:37:56 +0200
From: Ingo Molnar <mingo@...nel.org>
To: "Chang S. Bae" <chang.seok.bae@...el.com>
Cc: linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...capital.net>,
	Dave Hansen <dave@...1.net>, Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>, "H . Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 6/8] x86/fpu: Make sure x86_task_fpu() doesn't get called
 for PF_KTHREAD|PF_USER_WORKER tasks during exit


* Chang S. Bae <chang.seok.bae@...el.com> wrote:

> On 4/9/2025 2:11 PM, Ingo Molnar wrote:
> >   void arch_release_task_struct(struct task_struct *tsk)
> >   {
> > -	if (fpu_state_size_dynamic())
> > +	if (fpu_state_size_dynamic() && !(current->flags & (PF_KTHREAD | PF_USER_WORKER)))
> >   		fpstate_free(x86_task_fpu(tsk));
> >   }
> 
> Looks like the AMX system couldn't boot properly, and I found that
> referencing tsk->flags here resolves the issue.

Indeed, fixed!

I've also added your Fixed-by tag to the patch:

  Fixed-by: Chang S. Bae <chang.seok.bae@...el.com>

Thanks,

	Ingo

==========>

 arch/x86/kernel/process.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index de9df37c5d67..7a1bfb61d86f 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -109,7 +109,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 #ifdef CONFIG_X86_64
 void arch_release_task_struct(struct task_struct *tsk)
 {
-	if (fpu_state_size_dynamic() && !(current->flags & (PF_KTHREAD | PF_USER_WORKER)))
+	if (fpu_state_size_dynamic() && !(tsk->flags & (PF_KTHREAD | PF_USER_WORKER)))
 		fpstate_free(x86_task_fpu(tsk));
 }
 #endif