[PATCH for v5.3] cec-notifier: clear cec_adap in cec_notifier_unregister

[Hans Verkuil <hverkuil-cisco@xs4all.nl>]

If cec_notifier_cec_adap_unregister() is called before
cec_unregister_adapter() then everything is OK (and this is the
case today). But if it is the other way around, then
cec_notifier_unregister() is called first, and that doesn't
set n->cec_adap to NULL.

So if e.g. cec_notifier_set_phys_addr() is called after
cec_notifier_unregister() but before cec_unregister_adapter()
then n->cec_adap points to an unregistered and likely deleted
cec adapter. So just set n->cec_adap->notifier and n->cec_adap
to NULL for rubustness.

Eventually cec_notifier_unregister will disappear and this will
be simplified substantially.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
---
 drivers/media/cec/cec-notifier.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/media/cec/cec-notifier.c b/drivers/media/cec/cec-notifier.c
index 52a867bde15f..4d82a5522072 100644
--- a/drivers/media/cec/cec-notifier.c
+++ b/drivers/media/cec/cec-notifier.c
@@ -218,6 +218,8 @@ void cec_notifier_unregister(struct cec_notifier *n)

 	mutex_lock(&n->lock);
 	n->callback = NULL;
+	n->cec_adap->notifier = NULL;
+	n->cec_adap = NULL;
 	mutex_unlock(&n->lock);
 	cec_notifier_put(n);
 }
-- 
2.20.1