Commit b1a8de1f authored by chai wen's avatar chai wen Committed by Linus Torvalds

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.

[ update comment]
Signed-off-by: default avatarchai wen <>
Signed-off-by: default avatarDon Zickus <>
Cc: Ingo Molnar <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent f775da2f
......@@ -47,6 +47,7 @@ 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(bool, hard_watchdog_warn);
static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
......@@ -333,8 +334,22 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
/* only warn once */
if (__this_cpu_read(soft_watchdog_warn) == true)
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);
if (softlockup_all_cpu_backtrace) {
/* Prevent multiple soft-lockup reports if one cpu is already
......@@ -350,6 +365,7 @@ 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);
if (regs)
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