linux-kernel - [PATCH 1/3] watchdog/softlockup: Remove obsolete check of last reported task

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Date:   Thu, 24 Oct 2019 13:49:26 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Laurence Oberman <loberman@...hat.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org,
        Petr Mladek <pmladek@...e.com>
Subject: [PATCH 1/3] watchdog/softlockup: Remove obsolete check of last reported task

The commit 9cf57731b63e37ed995 ("watchdog/softlockup: Replace "watchdog/%u"
 threads with cpu_stop_work") caused that the watchdog is reliably touched
during a task switch.

As a result the check for a unnoticed task switch is not longer needed.
And the commit b1a8de1f534337b398c7778 ("softlockup: make detector be aware
of task switch of processes hogging cpu") can be reverted.

Signed-off-by: Petr Mladek <pmladek@...e.com>
---
 kernel/watchdog.c | 18 +-----------------
 1 file changed, 1 insertion(+), 17 deletions(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index f41334ef0971..b7e2046380cf 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -174,7 +174,6 @@ static DEFINE_PER_CPU(bool, softlockup_touch_sync);
 static DEFINE_PER_CPU(bool, soft_watchdog_warn);
 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
-static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
 static unsigned long soft_lockup_nmi_warn;
 
@@ -416,22 +415,8 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 			return HRTIMER_RESTART;
 
 		/* only warn once */
-		if (__this_cpu_read(soft_watchdog_warn) == true) {
-			/*
-			 * When multiple processes are causing softlockups the
-			 * softlockup detector only warns on the first one
-			 * because the code relies on a full quiet cycle to
-			 * re-arm.  The second process prevents the quiet cycle
-			 * and never gets reported.  Use task pointers to detect
-			 * this.
-			 */
-			if (__this_cpu_read(softlockup_task_ptr_saved) !=
-			    current) {
-				__this_cpu_write(soft_watchdog_warn, false);
-				__touch_watchdog();
-			}
+		if (__this_cpu_read(soft_watchdog_warn) == true)
 			return HRTIMER_RESTART;
-		}
 
 		if (softlockup_all_cpu_backtrace) {
 			/* Prevent multiple soft-lockup reports if one cpu is already
@@ -447,7 +432,6 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 		pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 			smp_processor_id(), duration,
 			current->comm, task_pid_nr(current));
-		__this_cpu_write(softlockup_task_ptr_saved, current);
 		print_modules();
 		print_irqtrace_events(current);
 		if (regs)
-- 
2.16.4