On 2018-04-11 07:09:13 [-0700], Tejun Heo wrote: > Hello, > > On Wed, Apr 11, 2018 at 03:56:43PM +0200, Vlastimil Babka wrote: > > > vmstat_update() is invoked by a kworker on a specific CPU. This worker > > > it bound to this CPU. The name of the worker was "kworker/1:1" so it > > > should have been a worker which was bound to CPU1. A worker which can > > > run on any CPU would have a `u' before the first digit. > > > > Oh my, and I have just been assured by Tejun that his cannot happen :) > > And yet, in the original report [1] I see: > > > > CPU: 0 PID: 269 Comm: kworker/1:1 Not tainted > > > > So is this perhaps related to the cpu hotplug that [1] mentions? e.g. is > > the cpu being hotplugged cpu 1, the worker started too early before > > stuff can be scheduled on the CPU, so it has to run on different than > > designated CPU? > > > > [1] https://marc.info/?l=linux-mm&m=152088260625433&w=2 > > The report says that it happens when hotplug is attempted. Per-cpu > doesn't pin the cpu alive, so if the cpu goes down while a work item > is in flight or a work item is queued while a cpu is offline it'll end > up executing on some other cpu. So, if a piece of code doesn't want > that happening, it gotta interlock itself - ie. start queueing when > the cpu comes online and flush and prevent further queueing when its > cpu goes down. I missed that cpuhotplug part while reading it. So in that case, let me add a CPU-hotplug notifier which cancels that work. After all it is not need once the CPU is gone. > Thanks. > Sebastian
