firmware: arm_sdei: Use cpus_read_lock() to avoid races with cpuhp

SDEI has private events that need registering and enabling on each CPU.
CPUs can come and go while we are trying to do this. SDEI tries to avoid
these problems by setting the reregister flag before the register call,
so any CPUs that come online register the event too. Sticking plaster
like this doesn't work, as if the register call fails, a CPU that
subsequently comes online will register the event before reregister
is cleared.

Take cpus_read_lock() around the register and enable calls. We don't
want surprise CPUs to do the wrong thing if they race with these calls
failing.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/drivers/firmware/arm_sdei.c b/drivers/firmware/arm_sdei.c
index f15f459e9df05c4a95a8c3491ab2b14978642b1d..45536408a8c1cbe1533ad91593b95ccc06c11a43 100644 (file)
--- a/drivers/firmware/arm_sdei.c
+++ b/drivers/firmware/arm_sdei.c
@@ -418,14 +418,19 @@ int sdei_event_enable(u32 event_num)
                return -ENOENT;
        }
 
-       spin_lock(&sdei_list_lock);
-       event->reenable = true;
-       spin_unlock(&sdei_list_lock);
 
+       cpus_read_lock();
        if (event->type == SDEI_EVENT_TYPE_SHARED)
                err = sdei_api_event_enable(event->event_num);
        else
                err = sdei_do_cross_call(_local_event_enable, event);
+
+       if (!err) {
+               spin_lock(&sdei_list_lock);
+               event->reenable = true;
+               spin_unlock(&sdei_list_lock);
+       }
+       cpus_read_unlock();
        mutex_unlock(&sdei_events_lock);
 
        return err;
@@ -627,21 +632,18 @@ int sdei_event_register(u32 event_num, sdei_event_callback *cb, void *arg)
                        break;
                }
 
-               spin_lock(&sdei_list_lock);
-               event->reregister = true;
-               spin_unlock(&sdei_list_lock);
-
+               cpus_read_lock();
                err = _sdei_event_register(event);
                if (err) {
-                       spin_lock(&sdei_list_lock);
-                       event->reregister = false;
-                       event->reenable = false;
-                       spin_unlock(&sdei_list_lock);
-
                        sdei_event_destroy(event);
                        pr_warn("Failed to register event %u: %d\n", event_num,
                                err);
+               } else {
+                       spin_lock(&sdei_list_lock);
+                       event->reregister = true;
+                       spin_unlock(&sdei_list_lock);
                }
+               cpus_read_unlock();
        } while (0);
        mutex_unlock(&sdei_events_lock);