Bastian Blank [bastian@xxxxxxxxxxxx] wrote: | On Mon, Dec 01, 2008 at 01:15:18PM -0800, Sukadev Bhattiprolu wrote: | > Greg Kurz [gkurz@xxxxxxxxxx] wrote: | > | On Thu, 2008-11-27 at 02:17 +0100, Bastian Blank wrote: | > | > On Tue, Nov 25, 2008 at 07:45:28PM -0800, Sukadev Bhattiprolu wrote: | > | > > Currently task_active_pid_ns is not safe to call after a | > | > > task becomes a zombie and exit_task_namespaces is called, | > | > > as nsproxy becomes NULL. | > | > Why do you need to be able to get the pid namespace from zombie | > | > processes? | > After exiting namespaces, the process notifies parent. With new changes | > to signals (in this patchset), the signal code may need to determine | > the namespace of sender (the exiting child in this case). | | So the parent of a process with a new pid namespace will never get a | SIGCHLD? I am wondering what I said that leads to that conclusion :-) If parent has a handler the handler will be called as usual otherwise SIGCHLD will be ignored. But anyway, an earlier version of my patches checked the pid namespace sooner and so I had to generalize task_active_pid_ns(). With the present order of checks in siginfo_from_ancestor_ns(), we don't need to generalize task_active_pid_ns(). SIG_FROM_USER flag will be clear when do_notify_parent() calls send_signal(). IOW, while we should eventually generalize task_active_pid_ns(), it is not required for this signals patchset and we can ignore patches 1 and 2 for now. | | What I read in the kernel source (kernel/signal.c:do_notify_parent, | include/asm-generic/siginfo.h:CLD_EXITED) is that the exit signals | (SIGCHLD) are describes as sent by the kernel. Yes. Are you suggesting a check like if (!is_si_special(info) && !SI_FROMKERNEL(info)) ? /* must be from user, safe to check ns */ But SI_ASYNCIO comes from the driver - so its not safe to check pid ns. (sent a separate query on SI_ASYNCIO). | | > | I agree with Eric and Sukadev that task_active_pid_ns() is unsafe. There | > | isn't even a /* don't use with zombies */ in pid_namespace.h... | > Hmm. Its not unsafe at present. It would become unsafe if the signals code | > tries to determine the namespace of sender. | | Why? Even now it may be used on zombie tasks. It used to be unsafe, and iirc was fixed a while ago(in part by moving exit_task_namespaces() into exit_notify()). Are you saying there is another path (outside these signals patches) where task_active_pid_ns() is called for zombies ? _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers