On 11/15/2013 03:19 AM, Tejun Heo wrote: > On Thu, Nov 14, 2013 at 05:25:29PM -0600, Shawn Bohrer wrote: >> In trying to reproduce the cgroup_mutex deadlock I reported earlier >> in https://lkml.org/lkml/2013/11/11/574 I believe I encountered a >> different issue that I'm also unable to understand. This machine >> started out reporting some soft lockups that look to me like they are >> on a read_lock(css_set_lock): >> > ... >> RIP: 0010:[<ffffffff8109253c>] [<ffffffff8109253c>] cgroup_attach_task+0xdc/0x7a0 > ... >> [<ffffffff81092e87>] attach_task_by_pid+0x167/0x1a0 >> [<ffffffff81092ef3>] cgroup_tasks_write+0x13/0x20 I've been getting this hang intermittently with the numad daemon running on CentOS/Fedora while running numa balancing tests. Started around 3.9 or so. > > Most likely the bug fixed by ea84753c98a7 ("cgroup: fix to break the > while loop in cgroup_attach_task() correctly"). 3.10.19 contains the > backported fix. > > Thanks. > Yes, that definitely looks like the right change -- and I ran post-3.12-rc6 for over a week without hitting the issue again. I'm willing to call that verified by since previously I couldn't go more than 2 days without encountering the bug. Ok, stupid question time since I stared at that loop several times while trying to figure out how things got stuck there. Apologies in advance if I'm just thick today -- but I'd really like to grok this bug. Are we getting some other thread from while_each_task() repeatedly keeping us in the loop? Or is there something else going on? The gut instinct is that calling something like while_each_task() on an exiting thread would either reliably give other threads in the group or quit [if the thread is the only one left in the group or if an exiting thread is no longer part of the group], but since that would make the continue work, obviously I'm missing something. Mel, I don't know how much time you've given to this since the last email, but this clears it up. Thanks for your time. Don Morris -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
