1 files changed, 134 insertions, 18 deletions

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 959d99583d1c..b2c1f14b8129 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -22,6 +22,8 @@
 #include <linux/sched/signal.h>
 #include <linux/sched/debug.h>
 #include <linux/sched/sysctl.h>
+#include <linux/hung_task.h>
+#include <linux/rwsem.h>
 
 #include <trace/events/sched.h>
 
@@ -31,6 +33,11 @@
 static int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
 
 /*
+ * Total number of tasks detected as hung since boot:
+ */
+static unsigned long __read_mostly sysctl_hung_task_detect_count;
+
+/*
  * Limit number of tasks checked in a batch.
  *
  * This value controls the preemptibility of khungtaskd since preemption
@@ -88,16 +95,19 @@ static struct notifier_block panic_block = {
 	.notifier_call = hung_task_panic,
 };
 
-static void check_hung_task(struct task_struct *t, unsigned long timeout)
+static bool task_is_hung(struct task_struct *t, unsigned long timeout)
 {
 	unsigned long switch_count = t->nvcsw + t->nivcsw;
+	unsigned int state = READ_ONCE(t->__state);
 
 	/*
-	 * Ensure the task is not frozen.
-	 * Also, skip vfork and any other user process that freezer should skip.
+	 * skip the TASK_KILLABLE tasks -- these can be killed
+	 * skip the TASK_IDLE tasks -- those are genuinely idle
+	 * skip the TASK_FROZEN task -- it reasonably stops scheduling by freezer
 	 */
-	if (unlikely(READ_ONCE(t->__state) & TASK_FROZEN))
-		return;
+	if (!(state & TASK_UNINTERRUPTIBLE) ||
+	    (state & (TASK_WAKEKILL | TASK_NOLOAD | TASK_FROZEN)))
+		return false;
 
 	/*
 	 * When a freshly created task is scheduled once, changes its state to
@@ -105,15 +115,119 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
 	 * musn't be checked.
 	 */
 	if (unlikely(!switch_count))
-		return;
+		return false;
 
 	if (switch_count != t->last_switch_count) {
 		t->last_switch_count = switch_count;
 		t->last_switch_time = jiffies;
-		return;
+		return false;
 	}
 	if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
+		return false;
+
+	return true;
+}
+
+#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER
+static void debug_show_blocker(struct task_struct *task, unsigned long timeout)
+{
+	struct task_struct *g, *t;
+	unsigned long owner, blocker, blocker_type;
+	const char *rwsem_blocked_by, *rwsem_blocked_as;
+
+	RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "No rcu lock held");
+
+	blocker = READ_ONCE(task->blocker);
+	if (!blocker)
+		return;
+
+	blocker_type = hung_task_get_blocker_type(blocker);
+
+	switch (blocker_type) {
+	case BLOCKER_TYPE_MUTEX:
+		owner = mutex_get_owner(hung_task_blocker_to_lock(blocker));
+		break;
+	case BLOCKER_TYPE_SEM:
+		owner = sem_last_holder(hung_task_blocker_to_lock(blocker));
+		break;
+	case BLOCKER_TYPE_RWSEM_READER:
+	case BLOCKER_TYPE_RWSEM_WRITER:
+		owner = (unsigned long)rwsem_owner(
+					hung_task_blocker_to_lock(blocker));
+		rwsem_blocked_as = (blocker_type == BLOCKER_TYPE_RWSEM_READER) ?
+					"reader" : "writer";
+		rwsem_blocked_by = is_rwsem_reader_owned(
+					hung_task_blocker_to_lock(blocker)) ?
+					"reader" : "writer";
+		break;
+	default:
+		WARN_ON_ONCE(1);
 		return;
+	}
+
+
+	if (unlikely(!owner)) {
+		switch (blocker_type) {
+		case BLOCKER_TYPE_MUTEX:
+			pr_err("INFO: task %s:%d is blocked on a mutex, but the owner is not found.\n",
+			       task->comm, task->pid);
+			break;
+		case BLOCKER_TYPE_SEM:
+			pr_err("INFO: task %s:%d is blocked on a semaphore, but the last holder is not found.\n",
+			       task->comm, task->pid);
+			break;
+		case BLOCKER_TYPE_RWSEM_READER:
+		case BLOCKER_TYPE_RWSEM_WRITER:
+			pr_err("INFO: task %s:%d is blocked on an rw-semaphore, but the owner is not found.\n",
+			       task->comm, task->pid);
+			break;
+		}
+		return;
+	}
+
+	/* Ensure the owner information is correct. */
+	for_each_process_thread(g, t) {
+		if ((unsigned long)t != owner)
+			continue;
+
+		switch (blocker_type) {
+		case BLOCKER_TYPE_MUTEX:
+			pr_err("INFO: task %s:%d is blocked on a mutex likely owned by task %s:%d.\n",
+			       task->comm, task->pid, t->comm, t->pid);
+			break;
+		case BLOCKER_TYPE_SEM:
+			pr_err("INFO: task %s:%d blocked on a semaphore likely last held by task %s:%d\n",
+			       task->comm, task->pid, t->comm, t->pid);
+			break;
+		case BLOCKER_TYPE_RWSEM_READER:
+		case BLOCKER_TYPE_RWSEM_WRITER:
+			pr_err("INFO: task %s:%d <%s> blocked on an rw-semaphore likely owned by task %s:%d <%s>\n",
+			       task->comm, task->pid, rwsem_blocked_as, t->comm,
+			       t->pid, rwsem_blocked_by);
+			break;
+		}
+		/* Avoid duplicated task dump, skip if the task is also hung. */
+		if (!task_is_hung(t, timeout))
+			sched_show_task(t);
+		return;
+	}
+}
+#else
+static inline void debug_show_blocker(struct task_struct *task, unsigned long timeout)
+{
+}
+#endif
+
+static void check_hung_task(struct task_struct *t, unsigned long timeout)
+{
+	if (!task_is_hung(t, timeout))
+		return;
+
+	/*
+	 * This counter tracks the total number of tasks detected as hung
+	 * since boot.
+	 */
+	sysctl_hung_task_detect_count++;
 
 	trace_sched_process_hang(t);
 
@@ -136,9 +250,12 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
 			print_tainted(), init_utsname()->release,
 			(int)strcspn(init_utsname()->version, " "),
 			init_utsname()->version);
+		if (t->flags & PF_POSTCOREDUMP)
+			pr_err("      Blocked by coredump.\n");
 		pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
 			" disables this message.\n");
 		sched_show_task(t);
+		debug_show_blocker(t, timeout);
 		hung_task_show_lock = true;
 
 		if (sysctl_hung_task_all_cpu_backtrace)
@@ -194,7 +311,6 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 	hung_task_show_lock = false;
 	rcu_read_lock();
 	for_each_process_thread(g, t) {
-		unsigned int state;
 
 		if (!max_count--)
 			goto unlock;
@@ -203,15 +319,8 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 				goto unlock;
 			last_break = jiffies;
 		}
-		/*
-		 * skip the TASK_KILLABLE tasks -- these can be killed
-		 * skip the TASK_IDLE tasks -- those are genuinely idle
-		 */
-		state = READ_ONCE(t->__state);
-		if ((state & TASK_UNINTERRUPTIBLE) &&
-		    !(state & TASK_WAKEKILL) &&
-		    !(state & TASK_NOLOAD))
-			check_hung_task(t, timeout);
+
+		check_hung_task(t, timeout);
 	}
  unlock:
 	rcu_read_unlock();
@@ -261,7 +370,7 @@ static int proc_dohung_task_timeout_secs(const struct ctl_table *table, int writ
  * and hung_task_check_interval_secs
  */
 static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
-static struct ctl_table hung_task_sysctls[] = {
+static const struct ctl_table hung_task_sysctls[] = {
 #ifdef CONFIG_SMP
 	{
 		.procname	= "hung_task_all_cpu_backtrace",
@@ -314,6 +423,13 @@ static struct ctl_table hung_task_sysctls[] = {
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= SYSCTL_NEG_ONE,
 	},
+	{
+		.procname	= "hung_task_detect_count",
+		.data		= &sysctl_hung_task_detect_count,
+		.maxlen		= sizeof(unsigned long),
+		.mode		= 0444,
+		.proc_handler	= proc_doulongvec_minmax,
+	},
 };
 
 static void __init hung_task_sysctl_init(void)