LU-14541 llite: Check for page deletion after fault

LU-14541 llite: Check for page deletion after fault

Before completing a page fault and returning to the kernel,
we lock the page and verify it has not been truncated.  But
we must also verify the page has not been deleted from
Lustre, or we can return a disconnected (ie, not tracked by
Lustre) page to the kernel.

We mark deleted pages !uptodate, but this doesn't matter
for faulted pages, because the kernel assumes they are
returned uptodate, and maps them in to the process address
space.  Once mapped, the page state is not checked until
the page is unmapped.

But because the page is referenced by the mapping, it stays
in the page cache even though it's been disconnected from
Lustre.

Because the page is disconnected from Lustre, it will not
be found and cancelled on lock cancellation.  This can
result in stale data reads.

This is particularly an issue with releasepage (called from
drop_caches or under memory pressure), which can delete
pages separately from cancelling covering locks.

If releasepage is disabled, which is effectively what
"LU-14541 llite: Check vmpage in releasepage"
does, this is not an issue.  But disabling releasepage
causes other problems and is incorrect anyway.

Lustre-change: https://review.whamcloud.com/49653
Lustre-commit: b3d2114e538cf95a7e036f8313e9095fe821da79

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: If1164db8f8e92a1cf811431d56d15f30d8eb3faa
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50598
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Qian Yingjin <qian@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>