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x86, fpu: copy_process: Sanitize fpu->last_cpu initialization

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Cosmetic, but imho memset(&dst->thread.fpu, 0) is not good simply
because it hides the (important) usage of ->has_fpu/etc from grep.
Change this code to initialize the members explicitly.

And note that ->last_cpu = 0 looks simply wrong, this can confuse
fpu_lazy_restore() if per_cpu(fpu_owner_task, 0) has already exited
and copy_process() re-allocated the same task_struct. Fortunately
this is not actually possible because child->fpu_counter == 0 and
thus fpu_lazy_restore() will not be called, but still this is not
clean/robust.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: http://lkml.kernel.org/r/20140902175727.GA21666@redhat.com
Reviewed-by: Suresh Siddha <sbsiddha@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Oleg Nesterov 2014-09-02 19:57:27 +02:00 committed by H. Peter Anvin
parent f1853505d9
commit 5e23fee23e
1 changed files with 3 additions and 1 deletions
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4
arch/x86/kernel/process.c
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@ -66,7 +66,9 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
{
*dst = *src;
memset(&dst->thread.fpu, 0, sizeof(dst->thread.fpu));
dst->thread.fpu.has_fpu = 0;
dst->thread.fpu.last_cpu = ~0;
dst->thread.fpu.state = NULL;
if (tsk_used_math(src)) {
int err = fpu_alloc(&dst->thread.fpu);
if (err)