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>

3 files changed, 1 insertions, 17 deletions

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 9da7b5f0c3a5..6f76f25c3ee8 100644
--- a/arch/powerpc/kernel/process.c
+++ b/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;
diff --git a/tools/testing/selftests/powerpc/dscr/dscr_inherit_exec_test.c b/tools/testing/selftests/powerpc/dscr/dscr_inherit_exec_test.c
index 8265504de571..08a8b95e3bc1 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr_inherit_exec_test.c
+++ b/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");
diff --git a/tools/testing/selftests/powerpc/dscr/dscr_inherit_test.c b/tools/testing/selftests/powerpc/dscr/dscr_inherit_test.c
index 4e414caf7f40..3e5a6d195e9a 100644
--- a/tools/testing/selftests/powerpc/dscr/dscr_inherit_test.c
+++ b/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");