Hello, James. On Thu, Jul 21, 2016 at 08:04:16AM -0700, James Bottomley wrote: > > I understand what you're trying to achieve but don't think cgroup's > > filesystem interface can accomodate that. To support that level of > > automatic delegation, the API should be providing enough isolation so > > that operations in one domain (user-specific operations) are > > transparent from the other (system-wide administration), which simply > > isn't true for cgroupfs. As a simple example, imagine a process > > being moved to another cgroup racing against the special operations > > you're describing ahead. Both sides are multi-step operations and > > there are no ways of synchronizing against each other from kernel > > side and the outcomes can easily be non-sensical. > > So if I understand, it's not about actually moving the tasks: echoing > the pid to the tasks file is atomic and we can mediate races there.
Yeah, each operation is atomic but most meaningul operations are multi-step. > It's about the debris left behind if the admin (or someone with > delegated authority) moves the task to a wholly different cgroup. > > Now we have a cgroup directory in the old cgroup, which the current > task has been removed from, for which the current user has permissions > and could then move the task back to. Is that the essence of the > problem? That'd be one side. The other side is the one moving. Let's say the system admin thing wants to move all processe from A proper to B. It would do that by draining processes from A's procs file into B's and even that is multistep and can race. Thanks. -- tejun
