[PATCH 5.4 041/309] usb: gadget: f_fs: set req->num_sgs as 0 for non-sg transfer

[Greg Kroah-Hartman]

From: Peter Chen <peter.chen@xxxxxxx>

commit d2450c6937018d40d4111fe830fa48d4ddceb8d0 upstream.

The UDC core uses req->num_sgs to judge if scatter buffer list is used.
Eg: usb_gadget_map_request_by_dev. For f_fs sync io mode, the request
is re-used for each request, so if the 1st request->length > PAGE_SIZE,
and the 2nd request->length is <= PAGE_SIZE, the f_fs uses the 1st
req->num_sgs for the 2nd request, it causes the UDC core get the wrong
req->num_sgs value (The 2nd request doesn't use sg). For f_fs async
io mode, it is not harm to initialize req->num_sgs as 0 either, in case,
the UDC driver doesn't zeroed request structure.

Cc: Jun Li <jun.li@xxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Fixes: 772a7a724f69 ("usb: gadget: f_fs: Allow scatter-gather buffers")
Signed-off-by: Peter Chen <peter.chen@xxxxxxx>
Signed-off-by: Felipe Balbi <balbi@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/usb/gadget/function/f_fs.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -1062,6 +1062,7 @@ static ssize_t ffs_epfile_io(struct file
 			req->num_sgs = io_data->sgt.nents;
 		} else {
 			req->buf = data;
+			req->num_sgs = 0;
 		}
 		req->length = data_len;
 
@@ -1105,6 +1106,7 @@ static ssize_t ffs_epfile_io(struct file
 			req->num_sgs = io_data->sgt.nents;
 		} else {
 			req->buf = data;
+			req->num_sgs = 0;
 		}
 		req->length = data_len;