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    SubjectRe: [PATCH v2 0/3] make vfork killable
    On Sat, Aug 13, 2011 at 06:18:14PM +0200, Tejun Heo wrote:
    > Hello, Oleg.
    > On Fri, Aug 12, 2011 at 07:55:50PM +0200, Oleg Nesterov wrote:
    > > > an alternative approach
    > > > could be handling vfork waiting as a type of job control stop.
    > >
    > > Well, I didn't see the code, but to be honest this doesn't look
    > > like a good idea to me. Firstly, personally I do not think this
    > > has something to do with the job control stop.
    > >
    > > And, to me sys_restart_syscall() looks like the very natural
    > > approach, and simple.
    > I've been playing with this and it does a bit further than
    > implementation simplicity. Currently, we have three different modes
    > of stopping a task.
    > * Regular job control and ptrace.
    > * vfork wait.
    > * cgroup freeze.
    > Currently, all three behave differently and the latter two use
    > UNINTERRUPTIBLE sleep causing rather nasty problems. If we want to
    > fix the UNINTERRUPTIBLE sleep problem, we end up introducing a new
    > user visible state no matter which way we go - ie. a task will be in a
    > state which isn't UNINTERRUPTIBLE sleep but still behave differently
    > in terms of signal delivery and job control.
    > What's needed is this different state of being stopped which reponds
    > to all kernel's desires (killing and ptracing) but stays stopped
    > regardless of what the user requests.
    > There's multiple ways to implement this and forced syscall restart is
    > one way to achieve it - ie. while the stop condition is pending,
    > syscall is forced to be restarted after interruption and re-enter
    > stop. The downside is that that wouldn't work with cgroup freeze at
    > all - there's no syscall to restart.
    > So, what I'm proposing is to basically add another job control state
    > which is similar to process group stop but controlled by other
    > parameters like vfork wait condition or control group frozen state.

    Are you proposing one new jobctl state for vfork and another for
    the cgroup freezer?

    > This allows these stops to be handled in a way very similar to already
    > esablished job control states including interaction with ptrace.

    Interesting. So long as shells and ptracers in containers would not see
    jobctl traps/events triggered by tasks outside the container it sounds

    -Matt Helsley

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