On 2019/07/25 23:25, Dmitry Safonov wrote:
> Yes, also current distributions already using the counter to print
> warnings number of times and then silently ignore. I.e., on my Arch
> Linux setup:
> hung_task_warnings:10
You can propose changing the default value of hung_task_warnings to -1.
Current patch might be inconvenient because printk() from hung_task_warning(t, false)
fails to go to consoles when that "t" was blocked for more than "timeout" seconds, for
if (sysctl_hung_task_panic) {
console_verbose();
hung_task_show_lock = true;
hung_task_call_panic = true;
}
path which is intended to force printk() to go to consoles is ignored by
/* Don't print warings twice */
if (!sysctl_hung_task_interval_warnings)
hung_task_warning(t, true);
when panic() should be called. (The vmcore would contain the printk() output which
was not sent to consoles if kdump is configured. But vmcore is not always available.)
> Yes, that's why it's disabled by default (=0).
> I tend to agree that printing with KERN_DEBUG may be better, but in my
> point of view the patch isn't enough justification for patching
> sched_show_task() and show_stack().
You can propose sched_show_task_log_lvl() and show_stack_log_lvl() like show_trace_log_lvl().
I think that sysctl_hung_task_interval_warnings should not be decremented automatically.
I guess that that variable should become a boolean which controls whether to report threads
(with KERN_DEBUG level) which was blocked for more than sysctl_hung_task_check_interval_secs
seconds (or a tristate which also controls whether the report should be sent to consoles
(because KERN_DEBUG level likely prevents sending to consoles)), and
hung_task_warning(t, false) should be called like
if (time_is_after_jiffies(t->last_switch_time + timeout * HZ)) {
if (sysctl_hung_task_interval_warnings)
hung_task_warning(t, false);
return;
}
rather than
if (sysctl_hung_task_interval_warnings)
hung_task_warning(t, false);
if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
return;
.
