mm/balloon_compaction: remove dependency on page lock

mm/balloon_compaction: remove dependency on page lock

Let's stop using the page lock in balloon code and instead use only the
balloon_device_lock.

As soon as we set the PG_movable_ops flag, we might now get isolation
callbacks for that page as we are no longer holding the page lock.  In
there, we'll simply synchronize using the balloon_device_lock.

So in balloon_page_isolate() lookup the balloon_dev_info through
page->private under balloon_device_lock.

It's crucial that we update page->private under the balloon_device_lock,
so the isolation callback can properly deal with concurrent deflation.

Consequently, make sure that balloon_page_finalize() is called under
balloon_device_lock as we remove a page from the list and clear
page->private.  balloon_page_insert() is already called with the
balloon_device_lock held.

Note that the core will still lock the pages, for example in
isolate_movable_ops_page().  The lock is there still relevant for handling
the PageMovableOpsIsolated flag, but that can be later changed to use an
atomic test-and-set instead, or moved into the movable_ops backends.

Link: https://lkml.kernel.org/r/20260119230133.3551867-10-david@kernel.org
Signed-off-by: David Hildenbrand (Red Hat) <david@kernel.org>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Eugenio Pérez <eperezma@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Jerrin Shaji George <jerrin.shaji-george@broadcom.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: SeongJae Park <sj@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>