watchdog/softlockup: Remove obsolete check of last reported task

commit 9cf57731b63e ("watchdog/softlockup: Replace "watchdog/%u" threads
 with cpu_stop_work") ensures that the watchdog is reliably touched during
a task switch.

As a result the check for an unnoticed task switch is not longer needed.

Remove the relevant code, which effectively reverts commit b1a8de1f5343
("softlockup: make detector be aware of task switch of processes hogging
cpu")

Signed-off-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Ziljstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20191024114928.15377-2-pmladek@suse.com

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 0621301..e3774e9 100644 (file)
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -173,7 +173,6 @@ static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
 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(struct task_struct *, softlockup_task_ptr_saved);
 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
 static unsigned long soft_lockup_nmi_warn;
 
@@ -413,22 +412,8 @@ 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
@@ -444,7 +429,6 @@ 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)