lkml.org 
[lkml]   [2018]   [Dec]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v5 4/7] cgroup: cgroup v2 freezer
    On 12/07, Roman Gushchin wrote:
    >
    > Cgroup v2 freezer tries to put tasks into a state similar to jobctl
    > stop. This means that tasks can be killed, ptraced (using
    > PTRACE_SEIZE*), and interrupted. It is possible to attach to
    > a frozen task, get some information (e.g. read registers) and detach.

    I fail to understand how this all supposed to work.

    > @@ -368,6 +369,8 @@ static inline int signal_pending_state(long state, struct task_struct *p)
    > return 0;
    > if (!signal_pending(p))
    > return 0;
    > + if (unlikely(cgroup_task_frozen(p) && p->jobctl == JOBCTL_TRAP_FREEZE))
    > + return __fatal_signal_pending(p);

    I think I will never agree with this change ;) and I don't think it actually helps.

    > +void cgroup_enter_frozen(void)
    > +{
    > + if (!current->frozen) {
    > + spin_lock_irq(&css_set_lock);
    > + current->frozen = true;
    > + cgroup_inc_frozen_cnt(task_dfl_cgroup(current), false, true);
    > + spin_unlock_irq(&css_set_lock);
    > + }
    > +
    > + __set_current_state(TASK_INTERRUPTIBLE);
    > + schedule();

    So once again, suppose it races with PTRACE_INTERRUPT, or SIGSTOP, or something
    else which should be handled by get_signal() before do_freezer_trap().

    If (say) PTRACE_INTERRUPT comes before schedule it will be lost. Otherwise
    the frozen task will react. This can't be right. Or I am totally confused.

    Perhaps you can split this patch? start with cgroup_enter_frozen() using
    TASK_KILLABLE, then teach it to handle ptrace/stop/etc? I think this way it
    would be simpler to discuss the necessary changes and document what exactly
    are you trying to do.

    and btw.... what about suspend? try_to_freeze_tasks() will obviously fail
    if there is a ->frozen thread?

    Oleg.

    \
     
     \ /
      Last update: 2018-12-11 17:27    [W:3.811 / U:0.060 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site