Since commit af4b8a83add95ef40716401395b44a1b579965f4 it's been possible to get into a situation where a pidns reaper is <defunct>, reparented to host pid 1, but never reaped. How to reproduce this is documented at
https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1168526 (and see https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1168526/comments/13) In short, run repeated starts of a container whose init is Process.exit(0); sysrq-t when such a task is playing zombie shows: [ 131.132978] init x ffff88011fc14580 0 2084 2039 0x00000000 [ 131.132978] ffff880116e89ea8 0000000000000002 ffff880116e89fd8 0000000000014580 [ 131.132978] ffff880116e89fd8 0000000000014580 ffff8801172a0000 ffff8801172a0000 [ 131.132978] ffff8801172a0630 ffff88011729fff0 ffff880116e14650 ffff88011729fff0 [ 131.132978] Call Trace: [ 131.132978] [<ffffffff816f6159>] schedule+0x29/0x70 [ 131.132978] [<ffffffff81064591>] do_exit+0x6e1/0xa40 [ 131.132978] [<ffffffff81071eae>] ? signal_wake_up_state+0x1e/0x30 [ 131.132978] [<ffffffff8106496f>] do_group_exit+0x3f/0xa0 [ 131.132978] [<ffffffff810649e4>] SyS_exit_group+0x14/0x20 [ 131.132978] [<ffffffff8170102f>] tracesys+0xe1/0xe6 Further debugging showed that every time this happened, zap_pid_ns_processes() started with nr_hashed being 3, while we were expecting it to drop to 2. Any time it didn't happen, nr_hashed was 1 or 2. So the reaper was waiting for nr_hashed to become 2, but free_pid() only wakes the reaper if nr_hashed hits 1. This patch makes free_pid() wake the reaper any time the reaper is PF_EXITING, to force it to re-test the pidns->nr_hashed = init_pids test. Note that this is more like what __unhash_process() used to do before af4b8a83add95ef40716401395b44a1b579965f4. Signed-off-by: Serge Hallyn <serge.hal...@ubuntu.com> Cc: "Eric W. Biederman" <ebied...@xmission.com> --- kernel/pid.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/pid.c b/kernel/pid.c index 0db3e79..6b312c4 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -274,6 +274,10 @@ void free_pid(struct pid *pid) case 0: schedule_work(&ns->proc_work); break; + default: + if (ns->child_reaper->flags & PF_EXITING) + wake_up_process(ns->child_reaper); + break; } } spin_unlock_irqrestore(&pidmap_lock, flags); -- 1.8.3.2 -- 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/
