[PATCH v4 00/15] follow_pfn and other iomap races

[Christoph Hellwig]

On Thu, Oct 29, 2020 at 10:38:16AM +0100, Daniel Vetter wrote:
> Hm so Jason and me discussed this, but e.g. the s390 is safe with with
> just the pagetable locks. So we'd need two versions.
> 
> The more practical problem is that I haven't found a reasonable way to
> check that a passed in mmu_notifier is registered against the mm we're
> working on, and without that check it feels a bit silly. But if you
> see how to do that I think we can do an EXPORT_SYMBOL_GPL follow_pfn
> which takes the notifier, and an __follow_pfn for s390 and similar
> internal code which isn't exported.

True, this is a bit of a mess.  So maybe just rename it to __follow_pfn,
proper documentation of the requirements and a switch to
EXPORT_SYMBOL_GPL.