Re: uninterruptible CLONE_VFORK (Was: oom: Make coredumpinterruptible)

[Roland McGrath]

> The parent can play with real_blocked or saved_sigmask to block all
> signals except STOP and KILL, use TASK_INTERRUPTIBLE for wait, and
> just return ERESTART each time it gets the signal (it should clear
> child->vfork_done if fatal_signal_pending).

Yes, perhaps.

> We should also check PF_KTHREAD though, there are in kernel users
> of CLONE_VFORK.

There is only __call_usermodehelper, but yes.

> > Bu the way that happens ordinarily is
> > to get all the way back to user mode and reenter with a normal syscall.
> > That doesn't touch the user stack itself, but it sure makes one nervous.
> 
> me too. Especially because I do not really know how !x86 machines
> implement this all.

The only problem I know of off hand is ia64's TIF_RESTORE_RSE (an
arch-specific ptrace detail).  But yes, it would require a careful
reading of all the arch code paths.

> We should also verify that the exiting/stopping parent can never write
> to its ->mm. For example, exit_mm() does put_user(tsk->clear_child_tid).
> Fortunately we can rely on PF_SIGNALED flag in this case.

Right.


Thanks,
Roland
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/