[tip:x86/fpu] x86, fpu: copy_process: Sanitize fpu-> last_cpu initialization

From: tip-bot for Oleg Nesterov
Date: Tue Sep 02 2014 - 18:19:57 EST

Commit-ID: 5e23fee23ea10730c752edce1777e6b7e727290f
Gitweb: http://git.kernel.org/tip/5e23fee23ea10730c752edce1777e6b7e727290f
Author: Oleg Nesterov <oleg@xxxxxxxxxx>
AuthorDate: Tue, 2 Sep 2014 19:57:27 +0200
Committer: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
CommitDate: Tue, 2 Sep 2014 14:51:16 -0700

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

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

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20140902175727.GA21666@xxxxxxxxxx
Reviewed-by: Suresh Siddha <sbsiddha@xxxxxxxxx>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
arch/x86/kernel/process.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index b9ba9d5..a44268c 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -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)
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