DAMON sysfs interface directly uses damon_ctx->kdamond field with manual
synchronization using damon_ctx->kdamond_lock, to get the pid of the
kdamond.  Use a new dedicated function for the purpose, namely
damon_kdamond_pid(), since that doesn't require manual and error-prone
synchronization.

Avoid use of kdamond_lock outside of the core.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 95fd9375a7d8..4de25708b05a 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1819,10 +1819,9 @@ static ssize_t pid_show(struct kobject *kobj,
 	if (!ctx)
 		goto out;
 
-	mutex_lock(&ctx->kdamond_lock);
-	if (ctx->kdamond)
-		pid = ctx->kdamond->pid;
-	mutex_unlock(&ctx->kdamond_lock);
+	pid = damon_kdamond_pid(ctx);
+	if (pid < 0)
+		pid = -1;
 out:
 	mutex_unlock(&damon_sysfs_lock);
 	return sysfs_emit(buf, "%d\n", pid);
-- 
2.47.3