powerpc: Fix DSCR inheritance over fork()

Two DSCR tests have a hack in them:

	/*
	 * XXX: Force a context switch out so that DSCR
	 * current value is copied into the thread struct
	 * which is required for the child to inherit the
	 * changed value.
	 */
	sleep(1);

We should not be working around this in the testcase, it is a kernel bug.
Fix it by copying the current DSCR to the child, instead of what we
had in the thread struct at last context switch.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/process.c

@@ -1287,7 +1287,7 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
 #ifdef CONFIG_PPC64 
 	if (cpu_has_feature(CPU_FTR_DSCR)) {
 		p->thread.dscr_inherit = current->thread.dscr_inherit;
-		p->thread.dscr = current->thread.dscr;
+		p->thread.dscr = mfspr(SPRN_DSCR);
 	}
 	if (cpu_has_feature(CPU_FTR_HAS_PPR))
 		p->thread.ppr = INIT_PPR;

tools/testing/selftests/powerpc/dscr/dscr_inherit_exec_test.c

@@ -60,14 +60,6 @@ int dscr_inherit_exec(void)
 		else
 			set_dscr(dscr);
 
-		/*
-		 * XXX: Force a context switch out so that DSCR
-		 * current value is copied into the thread struct
-		 * which is required for the child to inherit the
-		 * changed value.
-		 */
-		sleep(1);
-
 		pid = fork();
 		if (pid == -1) {
 			perror("fork() failed");

tools/testing/selftests/powerpc/dscr/dscr_inherit_test.c

@@ -40,14 +40,6 @@ int dscr_inherit(void)
 		else
 			set_dscr(dscr);
 
-		/*
-		 * XXX: Force a context switch out so that DSCR
-		 * current value is copied into the thread struct
-		 * which is required for the child to inherit the
-		 * changed value.
-		 */
-		sleep(1);
-
 		pid = fork();
 		if (pid == -1) {
 			perror("fork() failed");