mm/damon/lru_sort: handle ctx allocation failure

mm/damon/lru_sort: handle ctx allocation failure

DAMON_LRU_SORT allocates the damon_ctx object for its kdamond in its init
function.  damon_lru_sort_enabled_store() wrongly assumes the allocation
will always succeed once tried.  If the damon_ctx allocation was failed,
therefore, code execution reaches to damon_commit_ctx() while 'ctx' is
NULL.  As a result, it dereferences the NULL 'ctx' pointer.  Avoid the
NULL dereference by returning -ENOMEM if 'ctx' is NULL.

Link: https://lore.kernel.org/20260529000104.7006-3-sj@kernel.org
Fixes: c4a8e662c839 ("mm/damon/lru_sort: use damon_initialized()")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.18.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>