arch/tile: clean up tile-specific PTRACE_SETOPTIONS

Use the newer idioms for setting PTRACE_O_xxx and PT_TRACE_xxx flags.
Only set/clear tile-specific flags if the generic routine returns
success, since otherwise we want to avoid setting any flags at all.
Atomically update the ptrace flags with the new values.  Eliminate
the PT_TRACE_MASK_TILE bitmask and just shift PTRACE_O_MASK_TILE.
Add a BUILD_BUG_ON to avoid overlapping with generic bits.
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

arch/tile/include/asm/ptrace.h

@@ -24,8 +24,7 @@ typedef unsigned long pt_reg_t;
 #include <uapi/asm/ptrace.h>
 
 #define PTRACE_O_MASK_TILE	(PTRACE_O_TRACEMIGRATE)
-#define PT_TRACE_MIGRATE	0x00080000
-#define PT_TRACE_MASK_TILE	(PT_TRACE_MIGRATE)
+#define PT_TRACE_MIGRATE	PT_EVENT_FLAG(PTRACE_EVENT_MIGRATE)
 
 /* Flag bits in pt_regs.flags */
 #define PT_FLAGS_DISABLE_IRQ    1  /* on return to kernel, disable irqs */

arch/tile/include/uapi/asm/ptrace.h

@@ -81,8 +81,8 @@ struct pt_regs {
 #define PTRACE_SETFPREGS	15
 
 /* Support TILE-specific ptrace options, with events starting at 16. */
-#define PTRACE_O_TRACEMIGRATE	0x00010000
 #define PTRACE_EVENT_MIGRATE	16
+#define PTRACE_O_TRACEMIGRATE	(1 << PTRACE_EVENT_MIGRATE)
 
 /*
  * Flag bits in pt_regs.flags that are part of the ptrace API.

arch/tile/kernel/ptrace.c

@@ -151,12 +151,16 @@ long arch_ptrace(struct task_struct *child, long request,
 
 	case PTRACE_SETOPTIONS:
 		/* Support TILE-specific ptrace options. */
-		child->ptrace &= ~PT_TRACE_MASK_TILE;
+		BUILD_BUG_ON(PTRACE_O_MASK_TILE & PTRACE_O_MASK);
 		tmp = data & PTRACE_O_MASK_TILE;
 		data &= ~PTRACE_O_MASK_TILE;
 		ret = ptrace_request(child, request, addr, data);
-		if (tmp & PTRACE_O_TRACEMIGRATE)
-			child->ptrace |= PT_TRACE_MIGRATE;
+		if (ret == 0) {
+			unsigned int flags = child->ptrace;
+			flags &= ~(PTRACE_O_MASK_TILE << PT_OPT_FLAG_SHIFT);
+			flags |= (tmp << PT_OPT_FLAG_SHIFT);
+			child->ptrace = flags;
+		}
 		break;
 
 	default: