sched/debug: Add explicit TASK_IDLE printing

Markus reported that kthreads that idle using TASK_IDLE instead of
TASK_INTERRUPTIBLE are reported in as TASK_UNINTERRUPTIBLE and things
like htop mark those red.

This is undesirable, so add an explicit state for TASK_IDLE.
Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

fs/proc/array.c

@@ -119,18 +119,23 @@ static inline void task_name(struct seq_file *m, struct task_struct *p)
  * simple bit tests.
  */
 static const char * const task_state_array[] = {
-	"R (running)",		/*   0 */
-	"S (sleeping)",		/*   1 */
-	"D (disk sleep)",	/*   2 */
-	"T (stopped)",		/*   4 */
-	"t (tracing stop)",	/*   8 */
-	"X (dead)",		/*  16 */
-	"Z (zombie)",		/*  32 */
+
+	/* states in TASK_REPORT: */
+	"R (running)",		/* 0x00 */
+	"S (sleeping)",		/* 0x01 */
+	"D (disk sleep)",	/* 0x02 */
+	"T (stopped)",		/* 0x04 */
+	"t (tracing stop)",	/* 0x08 */
+	"X (dead)",		/* 0x10 */
+	"Z (zombie)",		/* 0x20 */
+
+	/* states beyond TASK_REPORT: */
+	"I (idle)",		/* 0x40 */
 };
 
 static inline const char *get_task_state(struct task_struct *tsk)
 {
-	BUILD_BUG_ON(1 + ilog2(TASK_REPORT) != ARRAY_SIZE(task_state_array) - 1);
+	BUILD_BUG_ON(1 + ilog2(TASK_REPORT_MAX) != ARRAY_SIZE(task_state_array));
 	return task_state_array[__get_task_state(tsk)];
 }
 

include/linux/sched.h

@@ -1241,22 +1241,30 @@ static inline pid_t task_pgrp_nr(struct task_struct *tsk)
 	return task_pgrp_nr_ns(tsk, &init_pid_ns);
 }
 
+#define TASK_REPORT_IDLE	(TASK_REPORT + 1)
+#define TASK_REPORT_MAX		(TASK_REPORT_IDLE << 1)
+
 static inline unsigned int __get_task_state(struct task_struct *tsk)
 {
 	unsigned int tsk_state = READ_ONCE(tsk->state);
 	unsigned int state = (tsk_state | tsk->exit_state) & TASK_REPORT;
 
+	BUILD_BUG_ON_NOT_POWER_OF_2(TASK_REPORT_MAX);
+
 	if (tsk_state == TASK_PARKED)
 		state = TASK_INTERRUPTIBLE;
 
+	if (tsk_state == TASK_IDLE)
+		state = TASK_REPORT_IDLE;
+
 	return fls(state);
 }
 
 static inline char __task_state_to_char(unsigned int state)
 {
-	static const char state_char[] = "RSDTtXZ";
+	static const char state_char[] = "RSDTtXZI";
 
-	BUILD_BUG_ON(1 + ilog2(TASK_REPORT) != sizeof(state_char) - 2);
+	BUILD_BUG_ON(1 + ilog2(TASK_REPORT_MAX) != sizeof(state_char) - 1);
 
 	return state_char[state];
 }

include/trace/events/sched.h

@@ -156,10 +156,11 @@ TRACE_EVENT(sched_switch,
 	TP_printk("prev_comm=%s prev_pid=%d prev_prio=%d prev_state=%s%s ==> next_comm=%s next_pid=%d next_prio=%d",
 		__entry->prev_comm, __entry->prev_pid, __entry->prev_prio,
 
-		(__entry->prev_state & TASK_REPORT) ?
-		  __print_flags(__entry->prev_state & TASK_REPORT, "|",
+		(__entry->prev_state & (TASK_REPORT_MAX - 1)) ?
+		  __print_flags(__entry->prev_state & (TASK_REPORT_MAX - 1), "|",
 				{ 0x01, "S" }, { 0x02, "D" }, { 0x04, "T" },
-				{ 0x08, "t" }, { 0x10, "X" }, { 0x20, "Z" }) :
+				{ 0x08, "t" }, { 0x10, "X" }, { 0x20, "Z" },
+				{ 0x40, "I" }) :
 		  "R",
 
 		__entry->prev_state & TASK_STATE_MAX ? "+" : "",