linux-kernel - [PATCH] kernel/hung_task.c: Use continuously blocked time when reporting.

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Message-Id: <1551175083-10669-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp>
Date:   Tue, 26 Feb 2019 18:58:03 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: [PATCH] kernel/hung_task.c: Use continuously blocked time when reporting.

Since commit a2e514453861dd39 ("kernel/hung_task.c: allow to set checking
interval separately from timeout") added hung_task_check_interval_secs,
setting a value different from hung_task_timeout_secs

  echo 0 > /proc/sys/kernel/hung_task_panic
  echo 120 > /proc/sys/kernel/hung_task_timeout_secs
  echo 5 > /proc/sys/kernel/hung_task_check_interval_secs

causes confusing output as if the task was blocked for
hung_task_timeout_secs seconds from the previous report.

  [  399.395930] INFO: task kswapd0:75 blocked for more than 120 seconds.
  [  405.027637] INFO: task kswapd0:75 blocked for more than 120 seconds.
  [  410.659725] INFO: task kswapd0:75 blocked for more than 120 seconds.
  [  416.292860] INFO: task kswapd0:75 blocked for more than 120 seconds.
  [  421.932305] INFO: task kswapd0:75 blocked for more than 120 seconds.

Although we could update t->last_switch_time after sched_show_task(t) if
we want to report only every 120 seconds, reporting every 5 seconds might
not be very bad for monitoring after a problematic situation has started.
Thus, let's use continuously blocked time instead of updating previously
reported time.

  [  677.985011] INFO: task kswapd0:80 blocked for more than 122 seconds.
  [  693.856126] INFO: task kswapd0:80 blocked for more than 138 seconds.
  [  709.728075] INFO: task kswapd0:80 blocked for more than 154 seconds.
  [  725.600018] INFO: task kswapd0:80 blocked for more than 170 seconds.
  [  741.473133] INFO: task kswapd0:80 blocked for more than 186 seconds.

Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
 kernel/hung_task.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 4a91916..6429139 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -126,7 +126,7 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
 		if (sysctl_hung_task_warnings > 0)
 			sysctl_hung_task_warnings--;
 		pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
-			t->comm, t->pid, timeout);
+		       t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
 		pr_err("      %s %s %.*s\n",
 			print_tainted(), init_utsname()->release,
 			(int)strcspn(init_utsname()->version, " "),
-- 
1.8.3.1