softlockup: decouple hung tasks check from softlockup detection

Decoupling allows:

* hung tasks check to happen at very low priority

* hung tasks check and softlockup to be enabled/disabled independently
  at compile and/or run-time

* individual panic settings to be enabled disabled independently
  at compile and/or run-time

* softlockup threshold to be reduced without increasing hung tasks
  poll frequency (hung task check is expensive relative to softlock watchdog)

* hung task check to be zero over-head when disabled at run-time

Signed-off-by: Mandeep Singh Baines <msb@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 10 insertions, 4 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 54cbabf3b871..f2f94d532302 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -297,9 +297,6 @@ extern int proc_dosoftlockup_thresh(struct ctl_table *table, int write,
                                     struct file *filp, void __user *buffer,
                                     size_t *lenp, loff_t *ppos);
 extern unsigned int  softlockup_panic;
-extern unsigned long sysctl_hung_task_check_count;
-extern unsigned long sysctl_hung_task_timeout_secs;
-extern unsigned long sysctl_hung_task_warnings;
 extern int softlockup_thresh;
 #else
 static inline void softlockup_tick(void)
@@ -316,6 +313,15 @@ static inline void touch_all_softlockup_watchdogs(void)
 }
 #endif
 
+#ifdef CONFIG_DETECT_HUNG_TASK
+extern unsigned int  sysctl_hung_task_panic;
+extern unsigned long sysctl_hung_task_check_count;
+extern unsigned long sysctl_hung_task_timeout_secs;
+extern unsigned long sysctl_hung_task_warnings;
+extern int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
+                                         struct file *filp, void __user *buffer,
+                                         size_t *lenp, loff_t *ppos);
+#endif
 
 /* Attach to any functions which should be ignored in wchan output. */
 #define __sched         __attribute__((__section__(".sched.text")))
@@ -1236,7 +1242,7 @@ struct task_struct {
 /* ipc stuff */
         struct sysv_sem sysvsem;
 #endif
-#ifdef CONFIG_DETECT_SOFTLOCKUP
+#ifdef CONFIG_DETECT_HUNG_TASK
 /* hung task detection */
         unsigned long last_switch_timestamp;
         unsigned long last_switch_count;