Re: [PATCH] mm/vmstat: flush per-cpu node stats when a node goes offline

[Gregory Price <gourry@gourry.net>]

On Sat, Jun 27, 2026 at 03:31:07AM -0400, Gregory Price wrote:
>  
>  	/*
>  	 * all memory/cpu of this node are removed, we can offline this
> -	 * node now.
> +	 * node now.  Fold any pending per-cpu vmstat diffs into the global
> +	 * counters first: once the node leaves the online set the periodic
> +	 * fold skips it, orphaning the residual on a later online.
>  	 */
> +	sync_vm_stats();

Sashiko points out this can deadlock on concurrent cpu hotplug, which
after a quick look seems accurate.

Has also made me realize the sync code is also racy with cpu hotplug
as well as it iterates per-online-cpu.

There are probably more races like this out there.

Will need to give this a little more thought.

>  	node_set_offline(nid);
>  	unregister_node(nid);
>  }