[PATCH 2/4] mm/damon/sysfs: propagate damon_call() error in turn_damon_on

[SJ Park <sj@kernel.org>]

From: Xuewen Wang <wangxuewen@kylinos.cn>

damon_sysfs_turn_damon_on() ignored the return value of damon_call()
for the repeat call control registration and always returned the stale
result of damon_start() (0 at that point). When damon_call() fails,
e.g., the kdamond is already exiting, the user still gets success from
the state file write while monitoring is not actually on.

Save and return the damon_call() result instead. No rollback of
damon_start() is needed since a failed damon_call() guarantees the
context is stopped.

Signed-off-by: Xuewen Wang <wangxuewen@kylinos.cn>
Reviewed-by: SJ Park <sj@kernel.org>
Signed-off-by: SJ Park <sj@kernel.org>
---
Changes from v1
- v1: https://lore.kernel.org/20260915093928.3389096-1-wangxuewen@kylinos.cn
- Collect R-b: from SJ.
- Rebase to the latest mm-new.

 mm/damon/sysfs.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 43519afb9eb7..70a4b64fb8ea 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -2607,7 +2607,8 @@ static int damon_sysfs_turn_damon_on(struct damon_sysfs_kdamond *kdamond)
 	repeat_call_control->data = kdamond;
 	repeat_call_control->repeat = true;
 	repeat_call_control->dealloc_on_cancel = true;
-	if (damon_call(ctx, repeat_call_control))
+	err = damon_call(ctx, repeat_call_control);
+	if (err)
 		kfree(repeat_call_control);
 	return err;
 }
-- 
2.47.3