Hello,
On Wed, Feb 19, 2020 at 10:32:31AM -0800, Marco Ballesio wrote:
> @@ -94,6 +94,18 @@ The following cgroupfs files are created by cgroup freezer.
> Shows the parent-state. 0 if none of the cgroup's ancestors is
> frozen; otherwise, 1.
>
> +* freezer.killable: Read-write
> +
> + When read, returns the killable state of a cgroup - "1" if frozen
> + tasks will respond to fatal signals, or "0" if they won't.
> +
> + When written, this property sets the killable state of the cgroup.
> + A value equal to "1" will switch the state of all frozen tasks in
> + the cgroup to TASK_INTERRUPTIBLE (similarly to cgroup v2) and will
> + make them react to fatal signals. A value of "0" will switch the
> + state of frozen tasks to TASK_UNINTERRUPTIBLE and they won't respond
> + to signals unless thawed or unfrozen.
As Roman said, I'm not too sure about adding a new cgroup1 freezer
interface at this point. If we do this, *maybe* a mount option would
be more minimal?
> diff --git a/kernel/freezer.c b/kernel/freezer.c
> index dc520f01f99d..92de1bfe62cf 100644
> --- a/kernel/freezer.c
> +++ b/kernel/freezer.c
> @@ -42,6 +42,9 @@ bool freezing_slow_path(struct task_struct *p)
> if (test_tsk_thread_flag(p, TIF_MEMDIE))
> return false;
>
> + if (cgroup_freezer_killable(p) && fatal_signal_pending(p))
> + return false;
> +
> if (pm_nosig_freezing || cgroup_freezing(p))
> return true;
>
> @@ -63,7 +66,12 @@ bool __refrigerator(bool check_kthr_stop)
> pr_debug("%s entered refrigerator\n", current->comm);
>
> for (;;) {
> - set_current_state(TASK_UNINTERRUPTIBLE);
> + bool killable = cgroup_freezer_killable(current);
> +
> + if (killable)
> + set_current_state(TASK_INTERRUPTIBLE);
> + else
> + set_current_state(TASK_UNINTERRUPTIBLE);
>
> spin_lock_irq(&freezer_lock);
> current->flags |= PF_FROZEN;
> @@ -75,6 +83,16 @@ bool __refrigerator(bool check_kthr_stop)
> if (!(current->flags & PF_FROZEN))
> break;
> was_frozen = true;
> +
> + /*
> + * Now we're sure that there is no pending fatal signal.
> + * Clear TIF_SIGPENDING to not get out of schedule()
> + * immediately (if there is a non-fatal signal pending), and
> + * put the task into sleep.
> + */
and this looks really racy to me. What happens if this task gets a
fatal signal here? We clear TIF_SIGPENDING and go to sleep?
> + if (killable)
> + clear_thread_flag(TIF_SIGPENDING);
> +
> schedule();
> }
Thanks.
--
tejun
