[PATCH] scheduler: enhancement to show_state_filter

[Yafang Shao]

Sometimes we want to get tasks in TASK_RUNNING sepcifically,
instead of dump all tasks.
For example, when the loadavg are high, we want to dump
tasks in TASK_RUNNING and TASK_UNINTERRUPTIBLE, which contribute
to system load. But mostly there're lots of tasks in Sleep state,
which occupies almost all of the kernel log buffer, even overflows
it, that causes the useful messages get lost. Although we can
enlarge the kernel log buffer, but that's not a good idea.

So I made this change to make the show_state_filter more flexible,
and then we can dump the tasks in TASK_RUNNING specifically.

Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
 drivers/tty/sysrq.c         | 2 +-
 include/linux/sched.h       | 1 +
 include/linux/sched/debug.h | 6 ++++--
 kernel/sched/core.c         | 7 ++++---
 4 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 3ffc1ce..86db51b 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -291,7 +291,7 @@ static void sysrq_handle_showstate(int key)
 
 static void sysrq_handle_showstate_blocked(int key)
 {
-	show_state_filter(TASK_UNINTERRUPTIBLE);
+	show_state_filter(TASK_UNINTERRUPTIBLE << 1);
 }
 static struct sysrq_key_op sysrq_showstate_blocked_op = {
 	.handler	= sysrq_handle_showstate_blocked,
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8337e2d..542a071 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -82,6 +82,7 @@
 #define TASK_NOLOAD			1024
 #define TASK_NEW			2048
 #define TASK_STATE_MAX			4096
+#define TASK_ALL_BITS			(TASK_STATE_MAX - 1)
 
 #define TASK_STATE_TO_CHAR_STR		"RSDTtXZxKWPNn"
 
diff --git a/include/linux/sched/debug.h b/include/linux/sched/debug.h
index e0eaee5..c844689 100644
--- a/include/linux/sched/debug.h
+++ b/include/linux/sched/debug.h
@@ -1,6 +1,8 @@
 #ifndef _LINUX_SCHED_DEBUG_H
 #define _LINUX_SCHED_DEBUG_H
 
+#include <linux/sched.h>
+
 /*
  * Various scheduler/task debugging interfaces:
  */
@@ -10,13 +12,13 @@
 extern void dump_cpu_task(int cpu);
 
 /*
- * Only dump TASK_* tasks. (0 for all tasks)
+ * Only dump TASK_* tasks. (TASK_ALL_BITS for all tasks)
  */
 extern void show_state_filter(unsigned long state_filter);
 
 static inline void show_state(void)
 {
-	show_state_filter(0);
+	show_state_filter(TASK_ALL_BITS);
 }
 
 struct pt_regs;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0869b20..46d277c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5161,19 +5161,20 @@ void show_state_filter(unsigned long state_filter)
 		 */
 		touch_nmi_watchdog();
 		touch_all_softlockup_watchdogs();
-		if (!state_filter || (p->state & state_filter))
+		/* in case we want to set TASK_RUNNING specifically */
+		if ((p->state != 0 ? p->state << 1 : 1) & state_filter)
 			sched_show_task(p);
 	}
 
 #ifdef CONFIG_SCHED_DEBUG
-	if (!state_filter)
+	if (state_filter == TASK_ALL_BITS)
 		sysrq_sched_debug_show();
 #endif
 	rcu_read_unlock();
 	/*
 	 * Only show locks if all tasks are dumped:
 	 */
-	if (!state_filter)
+	if (state_filter == TASK_ALL_BITS)
 		debug_show_all_locks();
 }
 
-- 
1.8.3.1