> On Jan 23, 2018, at 13:00, Jens Axboe <axboe@xxxxxxxxx> wrote: > > On 1/23/18 10:54 AM, David Zarzycki wrote: >> Hi Jens, >> >> The bug still reproduces with this change. How confident are we that >> kernel objects are properly reference counted while they are >> throttled? > > I would be surprised if it made a change, thanks for checking. Since > you're not pulling devices out of your system, is really nothing that > needs ref counting here. I’m not talking about hardware object reference counting, just basic memory management reference counting. That being said, I’m not a Linux kernel programmer, so I perhaps Linux avoids classic reference counting somehow. > You don't have something running turning wbt on/off during the run, I assume? I doubt it. This is just a plain Red Hat Fedora 27 workstation install with many of frills uninstalled afterwards. I didn’t even know that WBT could be dynamically enabled/disabled. > > The whole thing is very odd. You do have lots of processes exiting with > segfaults and similar. The only thing I can think of is the wait queue > entry becoming invalid since it's on the stack, but I don't see how that > can happen. We should exit the wait path normally and remove ourselves > from the list. For whatever it may be worth, I hit this bug once while rebuilding the Fedora kernel RPM, which is similar in that they both have short lived processes, but is different in that the Fedora kernel RPM rebuild doesn’t intentionally segfault to validate correctness. Dave
