The patch titled
Subject: softlockup: make detector be aware of task switch of processes hogging cpu
has been added to the -mm tree. Its filename is
softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu.patch
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------------------------------------------------------
From: chai wen <chaiw.fnst@xxxxxxxxxxxxxx>
Subject: softlockup: make detector be aware of task switch of processes hogging cpu
For now, soft lockup detector warns once for each case of process
softlockup. But the thread 'watchdog/n' may not always get the cpu at the
time slot between the task switch of two processes hogging that cpu to
reset soft_watchdog_warn.
An example would be two processes hogging the cpu. Process A causes the
softlockup warning and is killed manually by a user. Process B
immediately becomes the new process hogging the cpu preventing the
softlockup code from resetting the soft_watchdog_warn variable.
This case is a false negative of "warn only once for a process", as there
may be a different process that is going to hog the cpu. Resolve this by
saving/checking the task pointer of the hogging process and use that to
reset soft_watchdog_warn too.
Signed-off-by: chai wen <chaiw.fnst@xxxxxxxxxxxxxx>
Signed-off-by: Don Zickus <dzickus@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/watchdog.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff -puN kernel/watchdog.c~softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu kernel/watchdog.c
--- a/kernel/watchdog.c~softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu
+++ a/kernel/watchdog.c
@@ -47,6 +47,7 @@ static DEFINE_PER_CPU(bool, softlockup_t
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);
#ifdef CONFIG_HARDLOCKUP_DETECTOR
static DEFINE_PER_CPU(bool, hard_watchdog_warn);
static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
@@ -333,8 +334,20 @@ static enum hrtimer_restart watchdog_tim
return HRTIMER_RESTART;
/* only warn once */
- if (__this_cpu_read(soft_watchdog_warn) == true)
+ if (__this_cpu_read(soft_watchdog_warn) == true) {
+ /*
+ * Handle the case where multiple processes are
+ * causing softlockups but the duration is small
+ * enough, the softlockup detector can not reset
+ * itself in time. Use task pointers to detect this.
+ */
+ if (__this_cpu_read(softlockup_task_ptr_saved) !=
+ current) {
+ __this_cpu_write(soft_watchdog_warn, false);
+ __touch_watchdog();
+ }
return HRTIMER_RESTART;
+ }
if (softlockup_all_cpu_backtrace) {
/* Prevent multiple soft-lockup reports if one cpu is already
@@ -350,6 +363,7 @@ static enum hrtimer_restart watchdog_tim
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)
_
Patches currently in -mm which might be from chaiw.fnst@xxxxxxxxxxxxxx are
softlockup-make-detector-be-aware-of-task-switch-of-processes-hogging-cpu.patch
linux-next.patch
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