gpiolib: cdev: Cleanup kfifo_out() error handling

The handling of kfifo_out() errors in read functions obscures any error.
The error condition should never occur but, while a ret is set to -EIO, it
is subsequently ignored and the read functions instead return the number
of bytes copied to that point, potentially masking the fact that any error
occurred.

Log a warning and return -EIO in the case of a kfifo_out() error to make
it clear something very odd is going on here.

Signed-off-by: Kent Gibson <warthog618@gmail.com>
Link: https://lore.kernel.org/r/20240529131953.195777-4-warthog618@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index c7218c9f2c5e7daafe478fa7b423eaf3b4773c74..1cb952daacfb570e4194f28d6b24456b7f63927b 100644 (file)
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -1642,16 +1642,15 @@ static ssize_t linereq_read(struct file *file, char __user *buf,
                                        return ret;
                        }
 
-                       ret = kfifo_out(&lr->events, &le, 1);
-               }
-               if (ret != 1) {
-                       /*
-                        * This should never happen - we were holding the
-                        * lock from the moment we learned the fifo is no
-                        * longer empty until now.
-                        */
-                       ret = -EIO;
-                       break;
+                       if (kfifo_out(&lr->events, &le, 1) != 1) {
+                               /*
+                                * This should never happen - we hold the
+                                * lock from the moment we learned the fifo
+                                * is no longer empty until now.
+                                */
+                               WARN(1, "failed to read from non-empty kfifo");
+                               return -EIO;
+                       }
                }
 
                if (copy_to_user(buf + bytes_read, &le, sizeof(le)))
@@ -1995,16 +1994,15 @@ static ssize_t lineevent_read(struct file *file, char __user *buf,
                                        return ret;
                        }
 
-                       ret = kfifo_out(&le->events, &ge, 1);
-               }
-               if (ret != 1) {
-                       /*
-                        * This should never happen - we were holding the lock
-                        * from the moment we learned the fifo is no longer
-                        * empty until now.
-                        */
-                       ret = -EIO;
-                       break;
+                       if (kfifo_out(&le->events, &ge, 1) != 1) {
+                               /*
+                                * This should never happen - we hold the
+                                * lock from the moment we learned the fifo
+                                * is no longer empty until now.
+                                */
+                               WARN(1, "failed to read from non-empty kfifo");
+                               return -EIO;
+                       }
                }
 
                if (copy_to_user(buf + bytes_read, &ge, ge_size))
@@ -2707,12 +2705,15 @@ static ssize_t lineinfo_watch_read(struct file *file, char __user *buf,
                        if (count < event_size)
                                return -EINVAL;
 #endif
-                       ret = kfifo_out(&cdev->events, &event, 1);
-               }
-               if (ret != 1) {
-                       ret = -EIO;
-                       break;
-                       /* We should never get here. See lineevent_read(). */
+                       if (kfifo_out(&cdev->events, &event, 1) != 1) {
+                               /*
+                                * This should never happen - we hold the
+                                * lock from the moment we learned the fifo
+                                * is no longer empty until now.
+                                */
+                               WARN(1, "failed to read from non-empty kfifo");
+                               return -EIO;
+                       }
                }
 
 #ifdef CONFIG_GPIO_CDEV_V1