sparc64: Fix kernel thread stack termination.

Because of the silly way I set up the initial stack for
new kernel threads, there is a loop at the top of the
stack.

To fix this, properly add another stack frame that is copied
from the parent and terminate it in the child by setting
the frame pointer in that frame to zero.
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc64/kernel/process.c

@@ -657,20 +657,39 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long sp,
 		struct task_struct *p, struct pt_regs *regs)
 {
 	struct thread_info *t = task_thread_info(p);
+	struct sparc_stackf *parent_sf;
+	unsigned long child_stack_sz;
 	char *child_trap_frame;
+	int kernel_thread;
 
-	/* Calculate offset to stack_frame & pt_regs */
-	child_trap_frame = task_stack_page(p) + (THREAD_SIZE - (TRACEREG_SZ+STACKFRAME_SZ));
-	memcpy(child_trap_frame, (((struct sparc_stackf *)regs)-1), (TRACEREG_SZ+STACKFRAME_SZ));
+	kernel_thread = (regs->tstate & TSTATE_PRIV) ? 1 : 0;
+	parent_sf = ((struct sparc_stackf *) regs) - 1;
 
-	t->flags = (t->flags & ~((0xffUL << TI_FLAG_CWP_SHIFT) | (0xffUL << TI_FLAG_CURRENT_DS_SHIFT))) |
+	/* Calculate offset to stack_frame & pt_regs */
+	child_stack_sz = ((STACKFRAME_SZ + TRACEREG_SZ) +
+			  (kernel_thread ? STACKFRAME_SZ : 0));
+	child_trap_frame = (task_stack_page(p) +
+			    (THREAD_SIZE - child_stack_sz));
+	memcpy(child_trap_frame, parent_sf, child_stack_sz);
+
+	t->flags = (t->flags & ~((0xffUL << TI_FLAG_CWP_SHIFT) |
+				 (0xffUL << TI_FLAG_CURRENT_DS_SHIFT))) |
 		(((regs->tstate + 1) & TSTATE_CWP) << TI_FLAG_CWP_SHIFT);
 	t->new_child = 1;
 	t->ksp = ((unsigned long) child_trap_frame) - STACK_BIAS;
-	t->kregs = (struct pt_regs *)(child_trap_frame+sizeof(struct sparc_stackf));
+	t->kregs = (struct pt_regs *) (child_trap_frame +
+				       sizeof(struct sparc_stackf));
 	t->fpsaved[0] = 0;
 
-	if (regs->tstate & TSTATE_PRIV) {
+	if (kernel_thread) {
+		struct sparc_stackf *child_sf = (struct sparc_stackf *)
+			(child_trap_frame + (STACKFRAME_SZ + TRACEREG_SZ));
+
+		/* Zero terminate the stack backtrace.  */
+		child_sf->fp = NULL;
+		t->kregs->u_regs[UREG_FP] =
+		  ((unsigned long) child_sf) - STACK_BIAS;
+
 		/* Special case, if we are spawning a kernel thread from
 		 * a userspace task (via KMOD, NFS, or similar) we must
 		 * disable performance counters in the child because the
@@ -681,12 +700,7 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long sp,
 			t->pcr_reg = 0;
 			t->flags &= ~_TIF_PERFCTR;
 		}
-		t->kregs->u_regs[UREG_FP] = t->ksp;
 		t->flags |= ((long)ASI_P << TI_FLAG_CURRENT_DS_SHIFT);
-		flush_register_windows();
-		memcpy((void *)(t->ksp + STACK_BIAS),
-		       (void *)(regs->u_regs[UREG_FP] + STACK_BIAS),
-		       sizeof(struct sparc_stackf));
 		t->kregs->u_regs[UREG_G6] = (unsigned long) t;
 		t->kregs->u_regs[UREG_G4] = (unsigned long) t->task;
 	} else {