On Thu, Aug 29, 2013 at 10:44:41AM -0500, Serge Hallyn wrote: > Signalfd does not guarantee that we'll get an event for every signal. > So if 3 tasks exit at the same time, we may get only one sigchld > event. Therefore, in signal_handler(), always check whether init has > exited. Do with with WNOWAIT so that we can still wait4 to cleanup > the init after lxc_poll() exists (rather than complicating the code). > > Note - there is still a race in the kernel which can cause the > container init to become a defunct child of the host init (!). This > doesn't solve that, but is a potential (if very unlikely) race which > apw pointed out while we were trying to create a reproducer for the > kernel bug. > > Signed-off-by: Serge Hallyn <serge.hal...@ubuntu.com>
Acked-by: Stéphane Graber <stgra...@ubuntu.com>
> ---
> src/lxc/start.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/src/lxc/start.c b/src/lxc/start.c
> index f552e35..a574a8d 100644
> --- a/src/lxc/start.c
> +++ b/src/lxc/start.c
> @@ -162,8 +162,10 @@ static int signal_handler(int fd, void *data,
> struct lxc_epoll_descr *descr)
> {
> struct signalfd_siginfo siginfo;
> + siginfo_t info;
> int ret;
> pid_t *pid = data;
> + bool init_died = false;
>
> ret = read(fd, &siginfo, sizeof(siginfo));
> if (ret < 0) {
> @@ -176,16 +178,23 @@ static int signal_handler(int fd, void *data,
> return -1;
> }
>
> + // check whether init is running
> + info.si_pid = 0;
> + ret = waitid(P_PID, *pid, &info, WEXITED | WNOWAIT | WNOHANG);
> + if (ret == 0 && info.si_pid == *pid) {
> + init_died = true;
> + }
> +
> if (siginfo.ssi_signo != SIGCHLD) {
> kill(*pid, siginfo.ssi_signo);
> INFO("forwarded signal %d to pid %d", siginfo.ssi_signo, *pid);
> - return 0;
> + return init_died ? 1 : 0;
> }
>
> if (siginfo.ssi_code == CLD_STOPPED ||
> siginfo.ssi_code == CLD_CONTINUED) {
> INFO("container init process was stopped/continued");
> - return 0;
> + return init_died ? 1 : 0;
> }
>
> /* more robustness, protect ourself from a SIGCHLD sent
> @@ -193,7 +202,7 @@ static int signal_handler(int fd, void *data,
> */
> if (siginfo.ssi_pid != *pid) {
> WARN("invalid pid for SIGCHLD");
> - return 0;
> + return init_died ? 1 : 0;
> }
>
> DEBUG("container init process exited");
> --
> 1.8.3.2
>
>
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--
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com
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