Re: Random lockups on an email server - possibly kern/50168

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

   Date: Mon, 11 Apr 2016 10:01:13 -0400
   From: "D'Arcy J.M. Cain" <darcy%NetBSD.org@localhost>

   Crash didn't help.  When I pressed enter it dumped a ps output to the
   screen, probably the last command I ran when the system was up.  Here
   is a partial output of that as far back as screen would go.

   [...]

   I tried doing ps/n|more and crash just hung.

Trying to exec more may not work here.  Next time this happens, can
you just write down some of the pids from top output that are in
tstile, and ask crash to, e.g., `bt 0t18999'?  (`0t' means decimal
input, as opposed to the default hexadecimal.)

Another useful indication is the `flt_no' wchan (which likely means
one of the flt_noram[123456] waits), which suggests that the uvm pager
is stuck waiting for something -- probably waiting for the pager
daemon to do disk I/O, and all the other processes are probably stuck
waiting for a lock held by someone stuck in disk I/O.