[RFC PATCH 1/4] mm/damon/core: handle NULL ctx parameter in damon_call()

When NULL damon_ctx pointer parameter is passed, damon_call() could do
NULL dereference.  The caller is responsible to avoid that.  It is easy
to forget, and there are many damon_call() callers.  Meanwhile,
damon_call() is never meant to be performance critical.  It uses mutex
and completion.  Add the NULL pointer check inside damon_call() so that
callers can pass the parameter without NULL checks.

Signed-off-by: SJ Park <[email protected]>
---
 mm/damon/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 92631a36d7b51..5882f9c94c47f 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2188,6 +2188,8 @@ int damon_kdamond_pid(struct damon_ctx *ctx)
  */
 int damon_call(struct damon_ctx *ctx, struct damon_call_control *control)
 {
+	if (!ctx)
+		return -EINVAL;
 	if (!control->repeat)
 		init_completion(&control->completion);
 	control->canceled = false;
-- 
2.47.3