kernel: hung_task.c: disable on suspend

It is possible to observe hung_task complaints when system goes to
suspend-to-idle state:

 # echo freeze > /sys/power/state

 PM: Syncing filesystems ... done.
 Freezing user space processes ... (elapsed 0.001 seconds) done.
 OOM killer disabled.
 Freezing remaining freezable tasks ... (elapsed 0.002 seconds) done.
 sd 0:0:0:0: [sda] Synchronizing SCSI cache
 INFO: task bash:1569 blocked for more than 120 seconds.
       Not tainted 4.19.0-rc3_+ #687
 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
 bash            D    0  1569    604 0x00000000
 Call Trace:
  ? __schedule+0x1fe/0x7e0
  schedule+0x28/0x80
  suspend_devices_and_enter+0x4ac/0x750
  pm_suspend+0x2c0/0x310

Register a PM notifier to disable the detector on suspend and re-enable
back on wakeup.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 29 insertions, 1 deletions

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index b9132d1269ef..cb8e3e8ac7b9 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -15,6 +15,7 @@
 #include <linux/lockdep.h>
 #include <linux/export.h>
 #include <linux/sysctl.h>
+#include <linux/suspend.h>
 #include <linux/utsname.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/debug.h>
@@ -242,6 +243,28 @@ void reset_hung_task_detector(void)
 }
 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
 
+static bool hung_detector_suspended;
+
+static int hungtask_pm_notify(struct notifier_block *self,
+                              unsigned long action, void *hcpu)
+{
+        switch (action) {
+        case PM_SUSPEND_PREPARE:
+        case PM_HIBERNATION_PREPARE:
+        case PM_RESTORE_PREPARE:
+                hung_detector_suspended = true;
+                break;
+        case PM_POST_SUSPEND:
+        case PM_POST_HIBERNATION:
+        case PM_POST_RESTORE:
+                hung_detector_suspended = false;
+                break;
+        default:
+                break;
+        }
+        return NOTIFY_OK;
+}
+
 /*
  * kthread which checks for tasks stuck in D state
  */
@@ -261,7 +284,8 @@ static int watchdog(void *dummy)
                 interval = min_t(unsigned long, interval, timeout);
                 t = hung_timeout_jiffies(hung_last_checked, interval);
                 if (t <= 0) {
-                        if (!atomic_xchg(&reset_hung_task, 0))
+                        if (!atomic_xchg(&reset_hung_task, 0) &&
+                            !hung_detector_suspended)
                                 check_hung_uninterruptible_tasks(timeout);
                         hung_last_checked = jiffies;
                         continue;
@@ -275,6 +299,10 @@ static int watchdog(void *dummy)
 static int __init hung_task_init(void)
 {
         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
+
+        /* Disable hung task detector on suspend */
+        pm_notifier(hungtask_pm_notify, 0);
+
         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
 
         return 0;