Page reporting fetches pr_dev_info using rcu_access_pointer(), which is
for safely fetching a pointer that will not be dereferenced but could
concurrently updated. The code indeed does not dereference pr_dev_info
after fetcing it using rcu_access_pointer(), but it fetches the pointer
while concurrent updtes to the pointer is avoided by holding the update
side lock, page_reporting_mutex.
In the case, rcu_dereference_protected() is recommended because it
provides better readability and performance on some cases, as
rcu_dereference_protected() avoids use of READ_ONCE(). Replace the
rcu_access_pointer() calls with rcu_dereference_protected().
Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
---
mm/page_reporting.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index 79a8554f024c..079e0ebe1fb7 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -356,7 +356,7 @@ int page_reporting_register(struct page_reporting_dev_info *prdev)
mutex_lock(&page_reporting_mutex);
/* nothing to do if already in use */
- if (rcu_access_pointer(pr_dev_info)) {
+ if (rcu_dereference_protected(pr_dev_info, true)) {
err = -EBUSY;
goto err_out;
}
@@ -401,7 +401,7 @@ void page_reporting_unregister(struct page_reporting_dev_info *prdev)
{
mutex_lock(&page_reporting_mutex);
- if (rcu_access_pointer(pr_dev_info) == prdev) {
+ if (rcu_dereference_protected(pr_dev_info, true) == prdev) {
/* Disable page reporting notification */
RCU_INIT_POINTER(pr_dev_info, NULL);
synchronize_rcu();
--
2.25.1
