[PATCH] SysRq-X: show blocked tasks

Add SysRq-X support: show blocked (TASK_UNINTERRUPTIBLE) tasks only.

Useful for debugging IO stalls.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/char/sysrq.c

@@ -182,6 +182,18 @@ static struct sysrq_key_op sysrq_showstate_op = {
 	.enable_mask	= SYSRQ_ENABLE_DUMP,
 };
 
+static void sysrq_handle_showstate_blocked(int key, struct tty_struct *tty)
+{
+	show_state_filter(TASK_UNINTERRUPTIBLE);
+}
+static struct sysrq_key_op sysrq_showstate_blocked_op = {
+	.handler	= sysrq_handle_showstate_blocked,
+	.help_msg	= "showBlockedTasks",
+	.action_msg	= "Show Blocked State",
+	.enable_mask	= SYSRQ_ENABLE_DUMP,
+};
+
+
 static void sysrq_handle_showmem(int key, struct tty_struct *tty)
 {
 	show_mem();
@@ -304,7 +316,7 @@ static struct sysrq_key_op *sysrq_key_table[36] = {
 	/* May be assigned at init time by SMP VOYAGER */
 	NULL,				/* v */
 	NULL,				/* w */
-	NULL,				/* x */
+	&sysrq_showstate_blocked_op,	/* x */
 	NULL,				/* y */
 	NULL				/* z */
 };

include/linux/sched.h

@@ -194,7 +194,16 @@ extern void init_idle(struct task_struct *idle, int cpu);
 
 extern cpumask_t nohz_cpu_mask;
 
-extern void show_state(void);
+/*
+ * Only dump TASK_* tasks. (-1 for all tasks)
+ */
+extern void show_state_filter(unsigned long state_filter);
+
+static inline void show_state(void)
+{
+	show_state_filter(-1);
+}
+
 extern void show_regs(struct pt_regs *);
 
 /*

kernel/sched.c

@@ -4804,7 +4804,7 @@ static void show_task(struct task_struct *p)
 		show_stack(p, NULL);
 }
 
-void show_state(void)
+void show_state_filter(unsigned long state_filter)
 {
 	struct task_struct *g, *p;
 
@@ -4824,10 +4824,15 @@ void show_state(void)
 		 * console might take alot of time:
 		 */
 		touch_nmi_watchdog();
+		if (p->state & state_filter)
 			show_task(p);
 	} while_each_thread(g, p);
 
 	read_unlock(&tasklist_lock);
+	/*
+	 * Only show locks if all tasks are dumped:
+	 */
+	if (state_filter == -1)
 		debug_show_all_locks();
 }