linux-kernel - [PATCH RFC] kernel/hung_task.c: disable on suspend

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20180912161119.2692-1-vkuznets@redhat.com>
Date:   Wed, 12 Sep 2018 18:11:19 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH RFC] kernel/hung_task.c: disable on suspend

It is possible to observe hung_task complaints when system goes to
suspend-to-idle 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@...hat.com>
---
RFC: It really makes me wonder why nobody reported this before, makes
 me think I'm missing something.
---
 kernel/hung_task.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index b9132d1269ef..d75f288c016f 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 +243,24 @@ 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:
+		hung_detector_suspended = true;
+		break;
+	case PM_POST_SUSPEND:
+		hung_detector_suspended = false;
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}
+
 /*
  * kthread which checks for tasks stuck in D state
  */
@@ -261,7 +280,8 @@ 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 +295,10 @@ 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;
-- 
2.14.4