On Mon, Jul 29, 2019 at 01:20:58PM +0000, Stuart Henderson wrote: > On 2019-07-29, Raimo Niskanen <raimo+open...@erix.ericsson.se> wrote: > > A new hang, I tried to invstigate: > > > > At July 19 the last log entry from my 'ps' log was from 14:55, which is > > also the time on the 'systat vmstat' screen when it froze. Then the machine > > hums along but just after midnight at 00:42:01 the first "/bsd: process: > > table is full" entry appears. That message repeats until I rebooted it > > today at July 29 10:48. > > > > I had a terminal with top running. It was still updating. It showed about > > 98% sys and 2% spin on one of 4 CPUs, the others 100% idle. Then (after > > the process table had gotten full) it had 1282 idle processes and 1 on > > processor, which was 'top' itself. > > Memory: Real: 456M/1819M act/tot Free: 14G Cache: 676M Swap: 0K/16G. > > > > I had 8 shells under tmux ready for debugging. 'ls worked. > > 'systat' on one hung. 'top' on another failed with "cannot fork". > > 'exec ps ajxww" printed two lines with /sbin/init and /sbin/slaac > > and then hung. 'exec reboot' did not succeed. Neither did a short power > > button, that at least caused a printout "stopping daemon nginx(failed)", > > but got no further. I had to do a hard power off. > > > > My theory now is that our daily tests right before 14:55 started a process > > (this process is the top 'top' process with 10:14 execution time) that > > triggers a lock or other contention problem in the kernel which causes > > one CPU to spin in the system, and blocks processes from dying. > > About 10 hours later the process table gets full. > > > > Any, ANY ideas of how to proceed would be appreciated! > > > > Best Regards > > Did you notice any odd waitchan's (WAIT in top output)? > > Maybe set ddb.console=1 in sysctl.conf and reboot (if not already > set), then try to break into DDB during a hang and see how things look > in ps there. (Test breaking into DDB before a hang first so you know > that you can do it .. you can just "c" to continue). > > There might also be clues in things like "sh malloc" or "sh all pools". > > Perhaps you could also get clues from running a kernel built with > 'option WITNESS', you may get some messages in dmesg, or it adds commands > to ddb like "show locks", "show all locks", "show witness" (see ddb(4) for > details).
I have enabled Witness, it went so-so. We'll see what it catches. I downloaded 6.5 amd64 src.tar.gz and sys.tar.gz, unpacked them, applied all patches for stable 001-006 and built a kernel with: include "arch/amd64/conf/GENERIC" option MULTIPROCESSOR option MP_LOCKDEBUG option WITNESS Then I activated in /etc/sysctl.conf: ddb.console=1 kern.witness.locktrace=1 kern.witness.watch=3 For fun, I pressed Ctrl+Alt+Esc at the console, got a ddb> prompt and typed "show witness". It printed lots of info, I scrolled down to the end, but during the printout there was an UVM fault: Spin locks: /usr/src/sys/.... : bla bla bla : uvm_fault(0xffffffff81e03b50, 0xffff800022368360, 0, 1) -> e kernel: page fault trap, code=0 Faulted in DDB: continuing... Then I typed "cont" and it panicked. If anybody want details I took a picture. Have I combined too many debugging options, or is this sh*t that happens? Nevertheless, now the machine is running again, with Witness... I'll be back. > > Can you provoke a hang by running this process manually? -- / Raimo Niskanen, Erlang/OTP, Ericsson AB
