mm: allow ->huge_fault() to be called without the mmap_lock held

mm: allow ->huge_fault() to be called without the mmap_lock held

Remove the checks for the VMA lock being held, allowing the page fault
path to call into the filesystem instead of retrying with the mmap_lock
held.  This will improve scalability for DAX page faults.  Also update the
documentation to match (and fix some other changes that have happened
recently).

Link: https://lkml.kernel.org/r/20230818202335.2739663-3-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>