mm/damon/vaddr-test: fix memory leak in damon_do_test_apply_three_regions()

In the Linux kernel, the following vulnerability has been resolved:

mm/damon/vaddr-test: fix memory leak in damon_do_test_apply_three_regions()

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

Since commit 9f86d624292c ("mm/damon/vaddr-test: remove unnecessary
variables"), the damon_destroy_ctx() is removed, but still call
damon_new_target() and damon_new_region(), the damon_region which is
allocated by kmem_cache_alloc() in damon_new_region() and the damon_target
which is allocated by kmalloc in damon_new_target() are not freed. And
the damon_region which is allocated in damon_new_region() in
damon_set_regions() is also not freed.

So use damon_destroy_target to free all the damon_regions and damon_target.

unreferenced object 0xffff888107c9a940 (size 64):
comm "kunit_try_catch", pid 1069, jiffies 4294670592 (age 732.761s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 06 00 00 00 6b 6b 6b 6b ............kkkk
60 c7 9c 07 81 88 ff ff f8 cb 9c 07 81 88 ff ff `...............
backtrace:
[<ffffffff817e0167>] kmalloc_trace+0x27/0xa0
[<ffffffff819c11cf>] damon_new_target+0x3f/0x1b0
[<ffffffff819c7d55>] damon_do_test_apply_three_regions.constprop.0+0x95/0x3e0
[<ffffffff819c82be>] damon_test_apply_three_regions1+0x21e/0x260
[<ffffffff829fce6a>] kunit_generic_run_threadfn_adapter+0x4a/0x90
[<ffffffff81237cf6>] kthread+0x2b6/0x380
[<ffffffff81097add>] ret_from_fork+0x2d/0x70
[<ffffffff81003791>] ret_from_fork_asm+0x11/0x20
unreferenced object 0xffff8881079cc740 (size 56):
comm "kunit_try_catch", pid 1069, jiffies 4294670592 (age 732.761s)
hex dump (first 32 bytes):
05 00 00 00 00 00 00 00 14 00 00 00 00 00 00 00 ................
6b 6b 6b 6b 6b 6b 6b 6b 00 00 00 00 6b 6b 6b 6b kkkkkkkk....kkkk
backtrace:
[<ffffffff819bc492>] damon_new_region+0x22/0x1c0
[<ffffffff819c7d91>] damon_do_test_apply_three_regions.constprop.0+0xd1/0x3e0
[<ffffffff819c82be>] damon_test_apply_three_regions1+0x21e/0x260
[<ffffffff829fce6a>] kunit_generic_run_threadfn_adapter+0x4a/0x90
[<ffffffff81237cf6>] kthread+0x2b6/0x380
[<ffffffff81097add>] ret_from_fork+0x2d/0x70
[<ffffffff81003791>] ret_from_fork_asm+0x11/0x20
unreferenced object 0xffff888107c9ac40 (size 64):
comm "kunit_try_catch", pid 1071, jiffies 4294670595 (age 732.843s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 06 00 00 00 6b 6b 6b 6b ............kkkk
a0 cc 9c 07 81 88 ff ff 78 a1 76 07 81 88 ff ff ........x.v.....
backtrace:
[<ffffffff817e0167>] kmalloc_trace+0x27/0xa0
[<ffffffff819c11cf>] damon_new_target+0x3f/0x1b0
[<ffffffff819c7d55>] damon_do_test_apply_three_regions.constprop.0+0x95/0x3e0
[<ffffffff819c851e>] damon_test_apply_three_regions2+0x21e/0x260
[<ffffffff829fce6a>] kunit_generic_run_threadfn_adapter+0x4a/0x90
[<ffffffff81237cf6>] kthread+0x2b6/0x380
[<ffffffff81097add>] ret_from_fork+0x2d/0x70
[<ffffffff81003791>] ret_from_fork_asm+0x11/0x20
unreferenced object 0xffff8881079ccc80 (size 56):
comm "kunit_try_catch", pid 1071, jiffies 4294670595 (age 732.843s)
hex dump (first 32 bytes):
05 00 00 00 00 00 00 00 14 00 00 00 00 00 00 00 ................
6b 6b 6b 6b 6b 6b 6b 6b 00 00 00 00 6b 6b 6b 6b kkkkkkkk....kkkk
backtrace:
[<ffffffff819bc492>] damon_new_region+0x22/0x1c0
[<ffffffff819c7d91>] damon_do_test_apply_three_regions.constprop.0+0xd1/0x3e0
[<ffffffff819c851e>] damon_test_apply_three_regions2+0x21e/0x260
[<ffffffff829fce6a>] kunit_generic_run_threadfn_adapter+0x4a/0x90
[<ffffffff81237cf6>] kthread+0x2b6/0x380
[<ffffffff81097add>] ret_from_fork+0x2d/0x70
[<ffff
---truncated---