Hello, Oleg. On Tue, Nov 13, 2018 at 04:37:01PM +0100, Oleg Nesterov wrote: > On 11/12, Roman Gushchin wrote: > > > > This patch implements freezer for cgroup v2. However the functionality > > is similar, the interface is different to cgroup v1: it follows > > cgroup v2 interface principles. > > Oh, it seems that I actually need to apply this patch to (try to) understand > the details ;) Will try tomorrow. Yeah, it's a bit of a head spin like everything in signal delivery / ptrace paths. ... > OK, please forget for now, but perhaps it would be more clean to add > JOBCTL_TRAP_FREEZE to the JOBCTL_PENDING_MASK check in recalc_sigpending() > and change get_signal to check JOBCTL_TRAP_MASK | JOBCTL_TRAP_FREEZE; and > I am not even sure cgroup_freezer_enter() should live in do_jobctl_trap(). I'm sure you're aware of the context but just to refresh - one thing which was really broken about cgroup1 freezer was that it piggybacked on hibernation freezer and put frozen tasks in a state which is undefined when seen from userspace - they're just stuck in D sleep somewhere in the kernel. That's fine when the whole system is not gonna be running, but not when only a subportion is being frozen. So, the primary goal of cgroup2 freezer is putting the tasks in an equivalent state as jobctl stop. It's a jobctl stop but controlled by cgroup frozen state, meaning that they can be killed, PTRACE_SEIZE'd and INTERRUPT'ed (PTRACE_ATTACH doesn't work as signal delivery should be blocked but that's fine) and so on. Thanks. -- tejun
