[PATCH 3.17 052/319] x86, fpu: __restore_xstate_sig()->math_state_restore() needs preempt_disable()

[Greg Kroah-Hartman]

3.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Oleg Nesterov <oleg@xxxxxxxxxx>

commit df24fb859a4e200d9324e2974229fbb7adf00aef upstream.

Add preempt_disable() + preempt_enable() around math_state_restore() in
__restore_xstate_sig(). Otherwise __switch_to() after __thread_fpu_begin()
can overwrite fpu->state we are going to restore.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20140902175717.GA21649@xxxxxxxxxx
Reviewed-by: Suresh Siddha <sbsiddha@xxxxxxxxx>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/x86/kernel/xsave.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -402,8 +402,11 @@ int __restore_xstate_sig(void __user *bu
 			set_used_math();
 		}
 
-		if (use_eager_fpu())
+		if (use_eager_fpu()) {
+			preempt_disable();
 			math_state_restore();
+			preempt_enable();
+		}
 
 		return err;
 	} else {


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