On Mon 15-11-21 22:52:27, Dennis Zhou wrote:
On Mon, Nov 15, 2021 at 11:11:44PM +0000, Alexey Makhalov wrote:
On Nov 15, 2021, at 4:58 AM, Michal Hocko mhocko@suse.com wrote:
On Mon 15-11-21 11:04:16, Alexey Makhalov wrote:
Hi Michal,
I have asked several times for details about the specific setup that has led to the reported crash. Without much success so far. Reproduction steps would be the first step. That would allow somebody to work on this at least if Alexey doesn't have time to dive into this deeper.
I didn’t know that repro steps are still not clear.
To reproduce the panic you need to have a system, where you can hot add the CPU that belongs to memoryless NUMA node which is not present and onlined yet. In other words, by hot adding CPU, you will add both CPU and NUMA node at the same time.
There seems to be something different in your setup because memory less nodes have reportedly worked on x86. I suspect something must be different in your setup. Maybe it is that you are adding a cpu that is outside of possible cpus intialized during boot time. Those should have their nodes initialized properly - at least per init_cpu_to_node. Your report doesn't really explain how the cpu is hotadded. Maybe you are trying to do something that has never been supported on x86.
Memoryless nodes are supported by x86. But hot add of such nodes not quite done.
I need some clarification here. It sounds like memoryless nodes work on x86, but hotplug + memoryless nodes isn't a supported use case or you're introducing it as a new use case?
If this is a new use case, then I'm inclined to say this patch should NOT go in and a proper fix should be implemented on hotplug's side. I don't want to be in the business of having/seeing this conversation reoccur because we just papered over this issue in percpu.
The patch still seems to be in the mmotm tree. I have sent a different fix candidate [1] which should be more robust and cover also other potential places.
[1] http://lkml.kernel.org/r/20211214100732.26335-1-mhocko@kernel.org