[PATCH] samples/damon/mtier: fail early if address range parameters are invalid

[Zenghui Yu <yuzenghui@huawei.com>]

The comment on top of `struct damon_region` clearly says that

    For any use case, @ar should be non-zero positive size.

which is now verified in damon_verify_new_region() if the kernel is built
with DAMON_DEBUG_SANITY.

The WARN_ONCE() can be triggered if the mtier sample module is enabled
before node{0,1}_{start,end}_addr have been properly initialized, which is
obviously not good.

 ------------[ cut here ]------------
 start 0 >= end 0
 WARNING: mm/damon/core.c:116 at damon_new_region+0xf0/0x118, CPU#39: bash/34144
 Call trace:
  damon_new_region+0xf0/0x118 (P)
  damon_sample_mtier_build_ctx+0xd4/0x368
  damon_sample_mtier_start+0x1c/0x90
  damon_sample_mtier_enable_store+0x98/0xb0
  param_attr_store+0xb4/0x128
  module_attr_store+0x2c/0x50
  sysfs_kf_write+0x58/0x90
  kernfs_fop_write_iter+0x16c/0x238
  vfs_write+0x2c0/0x370
  ksys_write+0x74/0x118
  __arm64_sys_write+0x24/0x38
  invoke_syscall+0xa8/0x118
  el0_svc_common.constprop.0+0x48/0xf0
  do_el0_svc+0x24/0x38
  el0_svc+0x54/0x370
  el0t_64_sync_handler+0xa0/0xe8
  el0t_64_sync+0x1ac/0x1b0
 ---[ end trace 0000000000000000 ]---

Fix it by checking the validity of parameters right before
damon_new_region() and fail early if they're invalid.

Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
---
 samples/damon/mtier.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/samples/damon/mtier.c b/samples/damon/mtier.c
index 775838a23d93..4a5d3fb12e1b 100644
--- a/samples/damon/mtier.c
+++ b/samples/damon/mtier.c
@@ -118,6 +118,9 @@ static struct damon_ctx *damon_sample_mtier_build_ctx(bool promote)
 	} else {
 		addr.start = promote ? node1_start_addr : node0_start_addr;
 		addr.end = promote ? node1_end_addr : node0_end_addr;
+
+		if (addr.start >= addr.end)
+			goto free_out;
 	}
 
 	region = damon_new_region(addr.start, addr.end);
-- 
2.33.0