Hi Tejun, Thanks for looking at this, can you review this V2 patch from Pavel? To me it makes sense even without 1/2 which I didn't even bother to read. At least as a simple workaround for now. On 07/09, Tejun Heo wrote: > > Hello, > > On Tue, Jul 09, 2024 at 03:05:21PM +0100, Pavel Begunkov wrote: > > > ----------------------------------------------------------------------- > > > Either way I have no idea whether a cgroup_task_frozen() task should > > > react to task_work_add(TWA_SIGNAL) or not. > > > > > > Documentation/admin-guide/cgroup-v2.rst says > > > > > > Writing "1" to the file causes freezing of the cgroup and all > > > descendant cgroups. This means that all belonging processes will > > > be stopped and will not run until the cgroup will be explicitly > > > unfrozen. > > > > > > AFAICS this is not accurate, they can run but can't return to user-mode. > > > So I guess task_work_run() is fine. > > > > IIUC it's a user facing doc, so maybe it's accurate enough from that > > perspective. But I do agree that the semantics around task_work is > > not exactly clear. > > A good correctness test for cgroup freezer is whether it'd be safe to > snapshot and restore the tasks in the cgroup while frozen. Well, I don't really understand what can snapshot/restore actually mean... I forgot everything about cgroup freezer and I am already sleeping, but even if we forget about task_work_add/TIF_NOTIFY_SIGNAL/etc, afaics ptrace can change the state of cgroup_task_frozen() task between snapshot and restore ? Oleg.
