FROMGIT: mm: run the fault-around code under the VMA lock

The map_pages fs method should be safe to run under the VMA lock instead
of the mmap lock.  This should have a measurable reduction in contention
on the mmap lock.

Link: https://lkml.kernel.org/r/20230724185410.1124082-9-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

(cherry picked from commit 7456c15600264d635293c91df1e0c0b5a1e73578
https: //git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-unstable)

Bug: 293665307
Change-Id: Iaa1b0c2deeade361b34118f41b5deb591268a269
Signed-off-by: Suren Baghdasaryan <surenb@google.com>