acpi: bus: check once more for an empty list after locking it

List could have become empty after the unlocked check that was made earlier,
so check again inside the lock.

Should fix https://bugzilla.redhat.com/show_bug.cgi?id=427765

Signed-off-by: Chuck Ebbert <cebbert@redhat.com>
Cc: <stable@kernel.org>
Cc: Len Brown <lenb@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
index 5b6760e0f957..2d1955c11833 100644
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c
@@ -373,10 +373,11 @@ int acpi_bus_receive_event(struct acpi_bus_event *event)
         }
 
         spin_lock_irqsave(&acpi_bus_event_lock, flags);
-        entry =
-            list_entry(acpi_bus_event_list.next, struct acpi_bus_event, node);
-        if (entry)
+        if (!list_empty(&acpi_bus_event_list)) {
+                entry = list_entry(acpi_bus_event_list.next,
+                                   struct acpi_bus_event, node);
                 list_del(&entry->node);
+        }
         spin_unlock_irqrestore(&acpi_bus_event_lock, flags);
 
         if (!entry)