On 07/31, Jürg Billeter wrote: > > PR_SET_KILLABLE clears the SIGNAL_UNKILLABLE flag. This allows > CLONE_NEWPID tasks to restore normal signal behavior, opting out of the > special signal protection for init processes. This prctl does not allow > setting the SIGNAL_UNKILLABLE flag, only clearing. > > The SIGNAL_UNKILLABLE flag, which is implicitly set for tasks cloned > with CLONE_NEWPID, has the effect of ignoring all signals (from > userspace) if the corresponding handler is set to SIG_DFL. The only > exceptions are SIGKILL and SIGSTOP and they are only accepted if raised > from an ancestor namespace. > > SIGINT, SIGQUIT and SIGTSTP are used in job control for ^C, ^\, ^Z. > While a task with the SIGNAL_UNKILLABLE flag could install handlers for > these signals, this is not sufficient to implement a shell that uses > CLONE_NEWPID for child processes: Ah. My question wasn't clear, sorry. Could you explain your use-case? Why a shell wants to use CLONE_NEWPID? And what do we actually want in, say, ^Z case? Just stop the child reaper or may be it would be better to stop the whole pid namespace? > * As SIGSTOP is ignored when raised from the SIGNAL_UNKILLABLE process > itself, it's not possible to implement the stop action in a custom > SIGTSTP handler. Yes. So may be we actually want to change __isig() paths to use SEND_SIG_FORCED (this is not that simple), or perhaps we can change __send_signal() to not drop SIGSTOP sent to itself, or may be we can even introduce SIG_DFL_EVEN_IF_INIT, I dunno. > * Many applications do not install handlers for these signals and > thus, job control won't work properly with unmodified applications. I can't understand this. An application should be changed anyway to do PR_SET_KILLABLE? Let me clarify. I am not arguing with this patch, probably it makes sense in any case. I am just trying to understand your real motivation for this change. > + case PR_SET_KILLABLE: > + if (arg2 != 1 || arg3 || arg4 || arg5) > + return -EINVAL; > + spin_lock_irq(&me->sighand->siglock); > + me->signal->flags &= ~SIGNAL_UNKILLABLE; > + spin_unlock_irq(&me->sighand->siglock); OK, but then you need to change the CLONE_PARENT/SIGNAL_UNKILLABLE check in copy_process(). Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
