x86, fpu: drop_fpu() before restoring new state from sigframe

No need to save the state with unlazy_fpu(), that is about to get overwritten
by the state from the signal frame. Instead use drop_fpu() and continue
to restore the new state.

Also fold the stop_fpu_preload() into drop_fpu().

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/1345842782-24175-2-git-send-email-suresh.b.siddha@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/include/asm/fpu-internal.h

@@ -448,17 +448,12 @@ static inline void save_init_fpu(struct task_struct *tsk)
 	preempt_enable();
 }
 
-static inline void stop_fpu_preload(struct task_struct *tsk)
-{
-	tsk->fpu_counter = 0;
-}
-
 static inline void drop_fpu(struct task_struct *tsk)
 {
 	/*
 	 * Forget coprocessor state..
 	 */
-	stop_fpu_preload(tsk);
+	tsk->fpu_counter = 0;
 	preempt_disable();
 	__drop_fpu(tsk);
 	preempt_enable();

arch/x86/kernel/xsave.c

@@ -382,16 +382,14 @@ int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)
 		struct xsave_struct *xsave = &tsk->thread.fpu.state->xsave;
 		struct user_i387_ia32_struct env;
 
-		stop_fpu_preload(tsk);
-		unlazy_fpu(tsk);
+		drop_fpu(tsk);
 
 		if (__copy_from_user(xsave, buf_fx, state_size) ||
-		    __copy_from_user(&env, buf, sizeof(env))) {
-			drop_fpu(tsk);
+		    __copy_from_user(&env, buf, sizeof(env)))
 			return -1;
-		}
 
 		sanitize_restored_xstate(tsk, &env, xstate_bv, fx_only);
+		set_used_math();
 	} else {
 		/*
 		 * For 64-bit frames and 32-bit fsave frames, restore the user