Hello, Dave. On Thu, Nov 19, 2015 at 11:18:36PM -0500, Dave Jones wrote: > One of my debian boxes got a systemd update. After rebooting, > I started seeing a use-after-free trace, followed by a lockup. > > I have two slightly different traces from separate boots, > which may give some clue as to how it's getting free'd in two ways.. > > http://codemonkey.org.uk/junk/IMG_0474.jpg > http://codemonkey.org.uk/junk/IMG_0476.jpg > > This isn't new, I booted back to 4.3, and hit slab debugging warnings > from the same code. (At the least it was broken differently) > > The WARN_ON referenced in the 2nd trace is this.. > > static void pids_cancel(struct pids_cgroup *pids, int num) > { > /* > * A negative count (or overflow for that matter) is invalid, > * and indicates a bug in the `pids` controller proper. > */ > WARN_ON_ONCE(atomic64_add_negative(-num, &pids->counter)); > }
I *think* I know what's going on. Zombies don't pin the css so if the cgroup gets removed, the free path may end up operating on a css which has already been freed. Will look more into it. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
