sched: Assert task state bits at build time

Since everybody is lazy and prone to forgetting things, make the
compiler help us a bit.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20091217121830.060186433@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 14 insertions, 8 deletions

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 96361e8fa3a8..f560325c444f 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -134,14 +134,14 @@ static inline void task_name(struct seq_file *m, struct task_struct *p)
  * simple bit tests.
  */
 static const char *task_state_array[] = {
-        "R (running)",          /*  0 */
-        "S (sleeping)",         /*  1 */
-        "D (disk sleep)",       /*  2 */
-        "T (stopped)",          /*  4 */
-        "t (tracing stop)",     /*  8 */
-        "Z (zombie)",           /* 16 */
-        "X (dead)",             /* 32 */
-        "x (dead)",             /* 64 */
+        "R (running)",          /*   0 */
+        "S (sleeping)",         /*   1 */
+        "D (disk sleep)",       /*   2 */
+        "T (stopped)",          /*   4 */
+        "t (tracing stop)",     /*   8 */
+        "Z (zombie)",           /*  16 */
+        "X (dead)",             /*  32 */
+        "x (dead)",             /*  64 */
         "K (wakekill)",         /* 128 */
         "W (waking)",           /* 256 */
 };
@@ -151,6 +151,8 @@ static inline const char *get_task_state(struct task_struct *tsk)
         unsigned int state = (tsk->state & TASK_REPORT) | tsk->exit_state;
         const char **p = &task_state_array[0];
 
+        BUILD_BUG_ON(1 + ilog2(TASK_STATE_MAX) != ARRAY_SIZE(task_state_array));
+
         while (state) {
                 p++;
                 state >>= 1;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 94858df38a87..37543876ddf5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -192,9 +192,13 @@ print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 #define TASK_DEAD               64
 #define TASK_WAKEKILL           128
 #define TASK_WAKING             256
+#define TASK_STATE_MAX          512
 
 #define TASK_STATE_TO_CHAR_STR "RSDTtZXxKW"
 
+extern char ___assert_task_state[1 - 2*!!(
+                sizeof(TASK_STATE_TO_CHAR_STR)-1 != ilog2(TASK_STATE_MAX)+1)];
+
 /* Convenience macros for the sake of set_task_state */
 #define TASK_KILLABLE           (TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)
 #define TASK_STOPPED            (TASK_WAKEKILL | __TASK_STOPPED)