xfs: bug fixes for 6.4-rcX

[Dave Chinner <david@fromorbit.com>]

Hi folks,

The following patches are fixes for recently discovered problems.
I'd like to consider them all for a 6.4-rc merge, though really only
patch 2 is a necessary recent regression fix.

The first patch addresses a long standing buffer UAF during shutdown
situations, where shutdown log item completions can race with CIL
abort and iclog log item completions.

The second patch addresses a small performance regression from the
6.3 allocator rewrite which is also a potential AGF-AGF deadlock
vector as it allows out-of-order locking.

The third patch is a change needed by patch 4, which I split out for
clarity. By itself it does nothing.

The fourth patch is a fix for a AGI->AGF->inode cluster buffer lock
ordering deadlock. This was introduced when we started pinning inode
cluster buffers in xfs_trans_log_inode() in 5.8 to fix long-standing
inode reclaim blocking issues, but I've only seen it in the wild
once on a system making heavy use of OVL and hence O_TMPFILE based
operations.

This has all passed through fstests without any issues being
detected, but wider testing would be appreciated along with review.

-Dave.