gpio: cdev: wake up linereq poll() on device unbind

Add a notifier block to the linereq structure and register it with the
gpio_device's device notifier. Upon reception of an event, wake up the
wait queue so that the user-space be forced out of poll() and need to go
into a new system call which will then fail due to the chip being gone.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Kent Gibson <warthog618@gmail.com>

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index bc1542544e49cb09241de56ab5f9f9dbb6b0e334..7d0c83127ccb755cfaefcaa42157d1af49d312bd 100644 (file)
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -555,6 +555,7 @@ struct line {
  * @label: consumer label used to tag GPIO descriptors
  * @num_lines: the number of lines in the lines array
  * @wait: wait queue that handles blocking reads of events
+ * @device_unregistered_nb: notifier block for receiving gdev unregister events
  * @event_buffer_size: the number of elements allocated in @events
  * @events: KFIFO for the GPIO events
  * @seqno: the sequence number for edge events generated on all lines in
@@ -569,6 +570,7 @@ struct linereq {
        const char *label;
        u32 num_lines;
        wait_queue_head_t wait;
+       struct notifier_block device_unregistered_nb;
        u32 event_buffer_size;
        DECLARE_KFIFO_PTR(events, struct gpio_v2_line_event);
        atomic_t seqno;
@@ -610,6 +612,17 @@ struct linereq {
         GPIO_V2_LINE_FLAG_EVENT_CLOCK_HTE | \
         GPIO_V2_LINE_EDGE_FLAGS)
 
+static int linereq_unregistered_notify(struct notifier_block *nb,
+                                      unsigned long action, void *data)
+{
+       struct linereq *lr = container_of(nb, struct linereq,
+                                         device_unregistered_nb);
+
+       wake_up_poll(&lr->wait, EPOLLIN | EPOLLERR);
+
+       return NOTIFY_OK;
+}
+
 static void linereq_put_event(struct linereq *lr,
                              struct gpio_v2_line_event *le)
 {
@@ -1567,6 +1580,10 @@ static void linereq_free(struct linereq *lr)
 {
        unsigned int i;
 
+       if (lr->device_unregistered_nb.notifier_call)
+               blocking_notifier_chain_unregister(&lr->gdev->device_notifier,
+                                                  &lr->device_unregistered_nb);
+
        for (i = 0; i < lr->num_lines; i++) {
                if (lr->lines[i].desc) {
                        edge_detector_stop(&lr->lines[i]);
@@ -1727,6 +1744,12 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
                        offset);
        }
 
+       lr->device_unregistered_nb.notifier_call = linereq_unregistered_notify;
+       ret = blocking_notifier_chain_register(&gdev->device_notifier,
+                                              &lr->device_unregistered_nb);
+       if (ret)
+               goto out_free_linereq;
+
        fd = get_unused_fd_flags(O_RDONLY | O_CLOEXEC);
        if (fd < 0) {
                ret = fd;