FROMLIST: mm: Allow fault_dirty_shared_page() to be called under the VMA lock

By making maybe_unlock_mmap_for_io() handle the VMA lock correctly,
we make fault_dirty_shared_page() safe to be called without the mmap
lock held.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reported-by: David Hildenbrand <david@redhat.com>
Tested-by: Suren Baghdasaryan <surenb@google.com>

Link: https://lore.kernel.org/all/20230812002033.1002367-1-willy@infradead.org/



Bug: 293665307
Change-Id: Ifed050cc4d194c538765ab403de09199b94c7b1b
Signed-off-by: Suren Baghdasaryan <surenb@google.com>