[PATCH] percpu: Sync vmalloc mappings in pcpu_alloc() and free_percpu()

[Joerg Roedel]

On Thu, Apr 30, 2020 at 10:39:19PM -0400, Steven Rostedt wrote:
> What's so damn special about alloc_percpu()? It's definitely not a fast
> path. And it's not used often.

Okay, I fixed it in the percpu code. It is definitly not a nice
solution, but having to call vmalloc_sync_mappings/unmappings() is not a
nice solution at any place in the code. Here is the patch which fixes
this issue for me. I am also not sure what to put in the Fixes tag, as
it is related to tracing code accessing per-cpu data from the page-fault
handler, not sure when this got introduced. Maybe someone else can
provide a meaningful Fixes- or stable tag.

I also have an idea in mind how to make this all more robust and get rid
of the vmalloc_sync_mappings/unmappings() interface, will show more when
I know it works the way I think it does.

Regards,

	Joerg