From c360bdc593b8a8b6e94166026728764085919cff Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Wed, 9 Apr 2025 23:11:25 +0200 Subject: [PATCH] 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: Chang S. Bae Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: Brian Gerst Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Link: https://lore.kernel.org/r/20250409211127.3544993-7-mingo@kernel.org --- arch/x86/kernel/fpu/core.c | 8 +++++++- arch/x86/kernel/process.c | 2 +- 2 files changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index e4c20908ee49d..4a2193892e5d9 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -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(); diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 5fb502c97b08d..7a1bfb61d86f4 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()) + if (fpu_state_size_dynamic() && !(tsk->flags & (PF_KTHREAD | PF_USER_WORKER))) fpstate_free(x86_task_fpu(tsk)); } #endif -- 2.47.2