mm/damon/core: initialize damos->walk_completed in damon_new_scheme()

The function for allocating and initialize a 'struct damos' object,
damon_new_scheme(), is not initializing damos->walk_completed field.  Only
damos_walk_complete() is setting the field.  Hence the field will be
eventually set and used correctly from second damos_walk() call for the
scheme.  But the first damos_walk() could mistakenly not walk on the
regions.  Actually, a common usage of DAMOS for taking an access pattern
snapshot is installing a monitoring-purpose DAMOS scheme, doing
damos_walk() to retrieve the snapshot, and then removing the scheme. 
DAMON user-space tool (damo) also gets runtime snapshot in the way.  Hence
the problem can continuously happen in such use cases.  Initialize it
properly in the allocation function.

Link: https://lkml.kernel.org/r/20250228174450.41472-1-sj@kernel.org
Fixes: bf0eaba0ff ("mm/damon/core: implement damos_walk()")
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/core.c

@@ -373,6 +373,7 @@ struct damos *damon_new_scheme(struct damos_access_pattern *pattern,
 	 * or damon_attrs are updated.
 	 */
 	scheme->next_apply_sis = 0;
+	scheme->walk_completed = false;
 	INIT_LIST_HEAD(&scheme->filters);
 	scheme->stat = (struct damos_stat){};
 	INIT_LIST_HEAD(&scheme->list);