linux-kernel - [PATCH 50/89] sched/core: Convert ___assert_task_state() link time assert to BUILD_BUG

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Date:   Mon,  6 Feb 2017 14:28:53 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Galbraith <efault@....de>,
        Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 50/89] sched/core: Convert ___assert_task_state() link time assert to BUILD_BUG_ON()

The length of TASK_STATE_TO_CHAR_STR was still checked using the old
link-time manual error method - convert it to BUILD_BUG_ON(). This
has a couple of advantages:

 - it's more obvious what's going on

 - it reduces the size and complexity of <linux/sched.h>

 - BUILD_BUG_ON() will fail during compilation, with a clearer
   error message than the link time assert.

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Mike Galbraith <efault@....de>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 include/linux/sched.h | 3 ---
 kernel/sched/core.c   | 3 +++
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 29262493c915..41ca94a982b6 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -74,9 +74,6 @@ struct task_group;
 
 #define TASK_STATE_TO_CHAR_STR "RSDTtXZxKWPNn"
 
-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_current_state */
 #define TASK_KILLABLE		(TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)
 #define TASK_STOPPED		(TASK_WAKEKILL | __TASK_STOPPED)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 568e773c528f..eee4ac12811a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5233,6 +5233,9 @@ void sched_show_task(struct task_struct *p)
 	int ppid;
 	unsigned long state = p->state;
 
+	/* Make sure the string lines up properly with the number of task states: */
+	BUILD_BUG_ON(sizeof(TASK_STATE_TO_CHAR_STR)-1 != ilog2(TASK_STATE_MAX)+1);
+
 	if (!try_get_task_stack(p))
 		return;
 	if (state)
-- 
2.7.4