HWPOISON: Clean up PR_MCE_KILL interface

While writing the manpage I noticed some shortcomings in the
current interface.

- Define symbolic names for all the different values
- Boundary check the kill mode values
- For symmetry add a get interface too. This allows library
code to get/set the current state.
- For consistency define a PR_MCE_KILL_DEFAULT value

Signed-off-by: Andi Kleen <ak@linux.intel.com>

2 files changed, 30 insertions, 5 deletions

diff --git a/include/linux/prctl.h b/include/linux/prctl.h
index 931150566ade..a3baeb2c2161 100644
--- a/include/linux/prctl.h
+++ b/include/linux/prctl.h
@@ -88,6 +88,18 @@
 #define PR_TASK_PERF_EVENTS_DISABLE             31
 #define PR_TASK_PERF_EVENTS_ENABLE              32
 
+/*
+ * Set early/late kill mode for hwpoison memory corruption.
+ * This influences when the process gets killed on a memory corruption.
+ */
 #define PR_MCE_KILL     33
+# define PR_MCE_KILL_CLEAR   0
+# define PR_MCE_KILL_SET     1
+
+# define PR_MCE_KILL_LATE    0
+# define PR_MCE_KILL_EARLY   1
+# define PR_MCE_KILL_DEFAULT 2
+
+#define PR_MCE_KILL_GET 34
 
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index 255475d163e0..f6afe07d6c0b 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1546,24 +1546,37 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
                         if (arg4 | arg5)
                                 return -EINVAL;
                         switch (arg2) {
-                        case 0:
+                        case PR_MCE_KILL_CLEAR:
                                 if (arg3 != 0)
                                         return -EINVAL;
                                 current->flags &= ~PF_MCE_PROCESS;
                                 break;
-                        case 1:
+                        case PR_MCE_KILL_SET:
                                 current->flags |= PF_MCE_PROCESS;
-                                if (arg3 != 0)
+                                if (arg3 == PR_MCE_KILL_EARLY)
                                         current->flags |= PF_MCE_EARLY;
-                                else
+                                else if (arg3 == PR_MCE_KILL_LATE)
                                         current->flags &= ~PF_MCE_EARLY;
+                                else if (arg3 == PR_MCE_KILL_DEFAULT)
+                                        current->flags &=
+                                                ~(PF_MCE_EARLY|PF_MCE_PROCESS);
+                                else
+                                        return -EINVAL;
                                 break;
                         default:
                                 return -EINVAL;
                         }
                         error = 0;
                         break;
-
+                case PR_MCE_KILL_GET:
+                        if (arg2 | arg3 | arg4 | arg5)
+                                return -EINVAL;
+                        if (current->flags & PF_MCE_PROCESS)
+                                error = (current->flags & PF_MCE_EARLY) ?
+                                        PR_MCE_KILL_EARLY : PR_MCE_KILL_LATE;
+                        else
+                                error = PR_MCE_KILL_DEFAULT;
+                        break;
                 default:
                         error = -EINVAL;
                         break;