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SubjectRe: [PATCH] hung_task: Allow printing warnings every check interval
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On 2019/07/25 2:02, Dmitry Safonov wrote:
> Hung task detector has one timeout and has two associated actions on it:
> - issuing warnings with names and stacks of blocked tasks
> - panic()
>
> We want switches to panic (and reboot) if there's a task
> in uninterruptible sleep for some minutes - at that moment something
> ugly has happened and the box needs a reboot.
> But we also want to detect conditions that are "out of range"
> or approaching the point of failure. Under such conditions we want
> to issue an "early warning" of an impending failure, minutes before
> the switch is going to panic.

Can't we do it by extending sysctl_hung_task_panic to accept values larger
than 1, and decrease by one when at least one thread was reported by each
check_hung_uninterruptible_tasks() check, and call panic() when
sysctl_hung_task_panic reached to 0 (or maybe 1 is simpler) ?

Hmm, might have the same problem regarding how/when to reset the counter.
If some userspace process can reset the counter, such process can trigger
SysRq-c when some period expired...

> It seems rather easy to add printing tasks and their stacks for
> notification and debugging purposes into hung task detector without
> complicating the code or major cost (prints are with KERN_INFO loglevel
> and so don't go on console, only into dmesg log).

Well, I don't think so. Might be noisy for systems without "quiet" kernel
command line option, and we can't pass KERN_DEBUG to e.g. sched_show_task()...

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