[tip:x86/fpu] x86, fpu: __restore_xstate_sig()-> math_state_restore() needs preempt_disable()

[tip-bot for Oleg Nesterov <tipbot@zytor.com>]

Commit-ID:  df24fb859a4e200d9324e2974229fbb7adf00aef
Gitweb:     http://git.kernel.org/tip/df24fb859a4e200d9324e2974229fbb7adf00aef
Author:     Oleg Nesterov <oleg@redhat.com>
AuthorDate: Tue, 2 Sep 2014 19:57:17 +0200
Committer:  H. Peter Anvin <hpa@linux.intel.com>
CommitDate: Tue, 2 Sep 2014 14:51:15 -0700

x86, fpu: __restore_xstate_sig()->math_state_restore() needs preempt_disable()

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@redhat.com>
Link: http://lkml.kernel.org/r/20140902175717.GA21649@redhat.com
Cc: <stable@vger.kernel.org> # v3.7+
Reviewed-by: Suresh Siddha <sbsiddha@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
---
 arch/x86/kernel/xsave.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index cf0b830..4c540c4 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -400,8 +400,11 @@ int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)
 			set_used_math();
 		}
 
-		if (use_eager_fpu())
+		if (use_eager_fpu()) {
+			preempt_disable();
 			math_state_restore();
+			preempt_enable();
+		}
 
 		return err;
 	} else {