firmware loader: fix device lifetime

Callers of request_firmware* must hold the reference count of
@device, otherwise it is easy to trigger oops since the firmware
loader device is the child of @device.

This patch adds comments about the usage. In fact, most of drivers
call request_firmware* in its probe() or open(), so the constraint
should be reasonable and can be satisfied.

Also this patch holds the reference count of @device before
schedule_work() in request_firmware_nowait() to avoid that
the @device is released after request_firmware_nowait returns
and before the worker function is scheduled.

Signed-off-by: Ming Lei <ming.lei@canonical.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index fc119ce6fdb8..7d3a83bb1318 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -742,6 +742,8 @@ err_put_dev:
  *      @name will be used as $FIRMWARE in the uevent environment and
  *      should be distinctive enough not to be confused with any other
  *      firmware image for this or any other device.
+ *
+ *      Caller must hold the reference count of @device.
  **/
 int
 request_firmware(const struct firmware **firmware_p, const char *name,
@@ -823,6 +825,7 @@ static void request_firmware_work_func(struct work_struct *work)
 
  out:
         fw_work->cont(fw, fw_work->context);
+        put_device(fw_work->device);
 
         module_put(fw_work->module);
         kfree(fw_work);
@@ -841,6 +844,8 @@ static void request_firmware_work_func(struct work_struct *work)
  * @cont: function will be called asynchronously when the firmware
  *      request is over.
  *
+ *      Caller must hold the reference count of @device.
+ *
  *      Asynchronous variant of request_firmware() for user contexts where
  *      it is not possible to sleep for long time. It can't be called
  *      in atomic contexts.
@@ -869,6 +874,7 @@ request_firmware_nowait(
                 return -EFAULT;
         }
 
+        get_device(fw_work->device);
         INIT_WORK(&fw_work->work, request_firmware_work_func);
         schedule_work(&fw_work->work);
         return 0;