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i387: fix up some fpu_counter confusion

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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 34ddc81a23 ("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 <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2012-02-20 10:24:09 -08:00
parent b01543dfe6
commit cea20ca3f3
3 changed files with 4 additions and 1 deletions
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3
arch/x86/include/asm/i387.h
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@ -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

1
arch/x86/kernel/process_32.c
View file

@ -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;

1
arch/x86/kernel/process_64.c
View file

@ -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);