[PATCH v6 09/16] firmware: arm_scmi: Protect device request lookup with RCU

The SCMI device request notifier looks up protocol OF nodes from the
active_protocols IDR. The IDR lookup can run concurrently with protocol
activation while probe is still registering protocols and creating their
SCMI devices.

Wrap the lookup in an RCU read-side critical section as required by the
IDR API for lockless readers.

Fixes: 53b8c25df708 ("firmware: arm_scmi: Add common notifier helpers")
Reported-by: Sashiko <[email protected]>
Signed-off-by: Sudeep Holla <[email protected]>
---
 drivers/firmware/arm_scmi/driver.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index f607557c04ad..a2871dca24dc 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -33,6 +33,7 @@
 #include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/processor.h>
+#include <linux/rcupdate.h>
 #include <linux/refcount.h>
 #include <linux/slab.h>
 #include <linux/xarray.h>
@@ -2958,7 +2959,9 @@ static int scmi_device_request_notifier(struct notifier_block *nb,
 	struct scmi_device_id *id_table = data;
 	struct scmi_info *info = req_nb_to_scmi_info(nb);
 
+	rcu_read_lock();
 	np = idr_find(&info->active_protocols, id_table->protocol_id);
+	rcu_read_unlock();
 	if (!np)
 		return NOTIFY_DONE;
 

-- 
2.43.0