----
Sorry for the double post - I got Pavel's email incorrect earlier.
Pavel: your email under FREEZER in MAINTAINERS is out of date...
----
Matt Helsley wrote:
> The CHECKPOINTING state prevents userspace from unfreezing tasks until
> sys_checkpoint() is finished. When doing container checkpoint userspace
> will do:
[...]
> /*
> + * cgroup freezer state changes made without the aid of the cgroup filesystem
> + * must go through this function to ensure proper locking is observed.
> + */
> +static int freezer_checkpointing(struct task_struct *task,
> + enum freezer_state next_state)
> +{
> + struct freezer *freezer;
> + enum freezer_state state;
> +
> + task_lock(task);
> + freezer = task_freezer(task);
> + spin_lock_irq(&freezer->lock);
> + state = freezer->state;
After "echo FROZEN > /freezer/0/freezer_state", it is likely that
freezer->state remains CGROUP_FREEZING --
Then, looking at freezer_read():
...
if (state == CGROUP_FREEZING) {
/* We change from FREEZING to FROZEN lazily if the cgroup was
* only partially frozen when we exitted write. */
update_freezer_state(cgroup, freezer);
state = freezer->state;
}
...
IOW, usually, only if someone reads the freezer_state file will
the freezer->status reliably reflect the state.
So, I searched for where else freezer->state is consulted, and found:
int cgroup_frozen(struct task_struct *task)
{
struct freezer *freezer;
enum freezer_state state;
task_lock(task);
freezer = task_freezer(task);
state = freezer->state;
task_unlock(task);
return state == CGROUP_FROZEN;
}
Which is called (only?) from kernel/power/process.c:thaw_tasks().
Here, too, unless some read from the freezer_state file, this
test will incorrectly fail.
Perhaps introduce a freezer_unlazy_state(freezer) helper, or a
a freezer_get_state(freezer) helper to use in those places ?
> + if ((state == CGROUP_FROZEN && next_state == CGROUP_CHECKPOINTING) ||
> + (state == CGROUP_CHECKPOINTING && next_state == CGROUP_FROZEN))
> + freezer->state = next_state;
> + spin_unlock_irq(&freezer->lock);
> + task_unlock(task);
> +
> + return state;
> +}
[...]
Oren.
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