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()...
