Revert "mm: init_mlocked_on_free_v3"

There was insufficient review and no agreement that this is the right
approach.

There are serious flaws with the implementation that make processes using
mlock() not even work with simple fork() [1] and we get reliable crashes
when rebooting.

Further, simply because we might be unmapping a single PTE of a large
mlocked folio, we shouldn't zero out the whole folio.

... especially because the code can also *corrupt* urelated memory because
	kernel_init_pages(page, folio_nr_pages(folio));

Could end up writing outside of the actual folio if we work with a tail
page.

Let's revert it.  Once there is agreement that this is the right approach,
the issues were fixed and there was reasonable review and proper testing,
we can consider it again.

[1] https://lkml.kernel.org/r/[email protected]

Link: https://lkml.kernel.org/r/[email protected]
Fixes: ba42b524a040 ("mm: init_mlocked_on_free_v3")
Signed-off-by: David Hildenbrand <[email protected]>
Reported-by: David Wang <[email protected]>
Closes: https://lore.kernel.org/lkml/[email protected]/
Reported-by: Lance Yang <[email protected]>
Closes: https://lkml.kernel.org/r/[email protected]
Acked-by: Lance Yang <[email protected]>
Cc: York Jasper Niebuhr <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Kees Cook <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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