Commit c360bdc5 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

x86/fpu: Make sure x86_task_fpu() doesn't get called for... 


x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER_WORKER tasks during exit

fpu__drop() and arch_release_task_struct() calls x86_task_fpu()
unconditionally, while the FPU context area will not be present
if it's the init task, and should not be in use when it's some
other type of kthread.

Return early for PF_KTHREAD or PF_USER_WORKER tasks. The debug
warning in x86_task_fpu() will catch any kthreads attempting to
use the FPU save area.

Fixed-by: default avatarChang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250409211127.3544993-7-mingo@kernel.org
parent ec2227e0

arch/x86/kernel/fpu/core.c

+7 −1
Original line number Diff line number Diff line
@@ -683,7 +683,13 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal, 
 */

void fpu__drop(struct task_struct *tsk)

{

	struct fpu *fpu = x86_task_fpu(tsk);

	struct fpu *fpu;



	/* PF_KTHREAD tasks do not use the FPU context area: */

	if (tsk->flags & (PF_KTHREAD | PF_USER_WORKER))

		return;



	fpu = x86_task_fpu(tsk);



	preempt_disable();

arch/x86/kernel/process.c

+1 −1
Original line number Diff line number Diff line
@@ -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())

	if (fpu_state_size_dynamic() && !(tsk->flags & (PF_KTHREAD | PF_USER_WORKER)))

		fpstate_free(x86_task_fpu(tsk));

}

#endif