This reverts commit b7f55d928e.
As explained by Linus in [*], write faults on a mmap region are reads
from a filesysten point of view, so taking the inode glock exclusively
on write faults is incorrect.
Instead, when a page is marked writable, the .page_mkwrite vm operation
will be called, which is where the exclusive lock taking needs to
happen. I got this wrong because of a broken test case that made me
believe .page_mkwrite isn't getting called when it actually is.
[*] https://lore.kernel.org/lkml/CAHk-=wj8EWr_D65i4oRSj2FTbrc6RdNydNNCGxeabRnwtoU=3Q@mail.gmail.com/
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
d5b8145455