From cea20ca3f3181fc36788a15bc65d1062b96a0a6c Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Mon, 20 Feb 2012 10:24:09 -0800 Subject: [PATCH] i387: fix up some fpu_counter confusion This makes sure we clear the FPU usage counter for newly created tasks, just so that we start off in a known state (for example, don't try to preload the FPU state on the first task switch etc). It also fixes a thinko in when we increment the fpu_counter at task switch time, introduced by commit 34ddc81a230b ("i387: re-introduce FPU state preloading at context switch time"). We should increment the *new* task fpu_counter, not the old task, and only if we decide to use that state (whether lazily or preloaded). Signed-off-by: Linus Torvalds --- arch/x86/include/asm/i387.h | 3 ++- arch/x86/kernel/process_32.c | 1 + arch/x86/kernel/process_64.c | 1 + 3 files changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h index a850b4d8d14..8df95849721 100644 --- a/arch/x86/include/asm/i387.h +++ b/arch/x86/include/asm/i387.h @@ -348,10 +348,10 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta if (__save_init_fpu(old)) fpu_lazy_state_intact(old); __thread_clear_has_fpu(old); - old->fpu_counter++; /* Don't change CR0.TS if we just switch! */ if (fpu.preload) { + new->fpu_counter++; __thread_set_has_fpu(new); prefetch(new->thread.fpu.state); } else @@ -359,6 +359,7 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta } else { old->fpu_counter = 0; if (fpu.preload) { + new->fpu_counter++; if (fpu_lazy_restore(new)) fpu.preload = 0; else diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c index 80bfe1ab003..bc32761bc27 100644 --- a/arch/x86/kernel/process_32.c +++ b/arch/x86/kernel/process_32.c @@ -214,6 +214,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, task_user_gs(p) = get_user_gs(regs); + p->fpu_counter = 0; p->thread.io_bitmap_ptr = NULL; tsk = current; err = -ENOMEM; diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 1fd94bc4279..8ad880b3bc1 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -286,6 +286,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, set_tsk_thread_flag(p, TIF_FORK); + p->fpu_counter = 0; p->thread.io_bitmap_ptr = NULL; savesegment(gs, p->thread.gsindex); -- 2.41.0