[PATCH v3] staging: gpib: Fix device reference leak in fmh_gpib driver

[Ma Ke <make24@iscas.ac.cn>]

The fmh_gpib driver contains a device reference count leak in
fmh_gpib_attach_impl() where driver_find_device() increases the
reference count of the device by get_device() when matching but this
reference is not properly decreased. Add put_device() in
fmh_gpib_detach(), which ensures that the reference count of the
device is correctly managed.

Found by code review.

Cc: stable@vger.kernel.org
Fixes: 8e4841a0888c ("staging: gpib: Add Frank Mori Hess FPGA PCI GPIB driver")
Signed-off-by: Ma Ke <make24@iscas.ac.cn>
---
Changes in v3:
- deleted the redundant put_device() to avoid double free as suggestions;
Changes in v2:
- modified the free operations as suggestions. Thanks for dan carpenter's instructions.
---
 drivers/staging/gpib/fmh_gpib/fmh_gpib.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/staging/gpib/fmh_gpib/fmh_gpib.c b/drivers/staging/gpib/fmh_gpib/fmh_gpib.c
index 4138f3d2bae7..efce01b39b9b 100644
--- a/drivers/staging/gpib/fmh_gpib/fmh_gpib.c
+++ b/drivers/staging/gpib/fmh_gpib/fmh_gpib.c
@@ -1517,6 +1517,11 @@ void fmh_gpib_detach(struct gpib_board *board)
 					   resource_size(e_priv->gpib_iomem_res));
 	}
 	fmh_gpib_generic_detach(board);
+
+	if (board->dev) {
+		put_device(board->dev);
+		board->dev = NULL;
+	}
 }
 
 static int fmh_gpib_pci_attach_impl(struct gpib_board *board,
-- 
2.17.1