mm/damon/core-test: fix memory leak in damon_new_ctx()

When CONFIG_DAMON_KUNIT_TEST=y and making CONFIG_DEBUG_KMEMLEAK=y and
CONFIG_DEBUG_KMEMLEAK_AUTO_SCAN=y, the below memory leak is detected.

The damon_ctx which is allocated by kzalloc() in damon_new_ctx() in
damon_test_ops_registration() and damon_test_set_attrs() are not freed. 
So use damon_destroy_ctx() to free it.  After applying this patch, the
following memory leak is never detected

    unreferenced object 0xffff2b49c6968800 (size 512):
      comm "kunit_try_catch", pid 350, jiffies 4294895294 (age 557.028s)
      hex dump (first 32 bytes):
        88 13 00 00 00 00 00 00 a0 86 01 00 00 00 00 00  ................
        00 87 93 03 00 00 00 00 0a 00 00 00 00 00 00 00  ................
      backtrace:
        [<0000000088e71769>] slab_post_alloc_hook+0xb8/0x368
        [<0000000073acab3b>] __kmem_cache_alloc_node+0x174/0x290
        [<00000000b5f89cef>] kmalloc_trace+0x40/0x164
        [<00000000eb19e83f>] damon_new_ctx+0x28/0xb4
        [<00000000daf6227b>] damon_test_ops_registration+0x34/0x328
        [<00000000559c4801>] kunit_try_run_case+0x50/0xac
        [<000000003932ed49>] kunit_generic_run_threadfn_adapter+0x20/0x2c
        [<000000003c3e9211>] kthread+0x124/0x130
        [<0000000028f85bdd>] ret_from_fork+0x10/0x20
    unreferenced object 0xffff2b49c1a9cc00 (size 512):
      comm "kunit_try_catch", pid 356, jiffies 4294895306 (age 557.000s)
      hex dump (first 32 bytes):
        88 13 00 00 00 00 00 00 a0 86 01 00 00 00 00 00  ................
        00 00 00 00 00 00 00 00 0a 00 00 00 00 00 00 00  ................
      backtrace:
        [<0000000088e71769>] slab_post_alloc_hook+0xb8/0x368
        [<0000000073acab3b>] __kmem_cache_alloc_node+0x174/0x290
        [<00000000b5f89cef>] kmalloc_trace+0x40/0x164
        [<00000000eb19e83f>] damon_new_ctx+0x28/0xb4
        [<00000000058495c4>] damon_test_set_attrs+0x30/0x1a8
        [<00000000559c4801>] kunit_try_run_case+0x50/0xac
        [<000000003932ed49>] kunit_generic_run_threadfn_adapter+0x20/0x2c
        [<000000003c3e9211>] kthread+0x124/0x130
        [<0000000028f85bdd>] ret_from_fork+0x10/0x20

Link: https://lkml.kernel.org/r/20230918120951.2230468-3-ruanjinjie@huawei.com
Fixes: d1836a3b ("mm/damon/core-test: initialise context before test in damon_test_set_attrs()")
Fixes: 4f540f5a ("mm/damon/core-test: add a kunit test case for ops registration")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Reviewed-by: Feng Tang <feng.tang@intel.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/core-test.h

@@ -269,6 +269,8 @@ static void damon_test_ops_registration(struct kunit *test)
 
 	/* Check double-registration failure again */
 	KUNIT_EXPECT_EQ(test, damon_register_ops(&ops), -EINVAL);
+
+	damon_destroy_ctx(c);
 }
 
 static void damon_test_set_regions(struct kunit *test)
@@ -346,6 +348,8 @@ static void damon_test_set_attrs(struct kunit *test)
 	invalid_attrs = valid_attrs;
 	invalid_attrs.aggr_interval = 4999;
 	KUNIT_EXPECT_EQ(test, damon_set_attrs(c, &invalid_attrs), -EINVAL);
+
+	damon_destroy_ctx(c);
 }
 
 static void damon_test_moving_sum(struct kunit *test)