usb: gadget: ffs: fix: Always call ffs_closed() in ffs_data_clear()

Originally FFS_FL_CALL_CLOSED_CALLBACK flag has been used to
indicate if we should call ffs_closed_callback().

Commit 4b187fceec3c ("usb: gadget: FunctionFS: add devices
management code") changed its semantic to indicate if we should
call ffs_closed() function which does a little bit more.

This situation leads to:

[  122.362269] ------------[ cut here ]------------
[  122.362287] WARNING: CPU: 2 PID: 2384 at drivers/usb/gadget/function/f_fs.c:3417 ffs_ep0_write+0x730/0x810 [usb_f_fs]()
[  122.362292] Modules linked in:
[  122.362555] CPU: 2 PID: 2384 Comm: adbd Tainted: G        W       4.1.0-0.rc4.git0.1.1.fc22.i686 #1
[  122.362561] Hardware name: To be filled by O.E.M. To be filled by O.E.M./Aptio CRB, BIOS 5.6.5 07/25/2014
[  122.362567]  c0d1f947 415badfa 00000000 d1029e64 c0a86e54 00000000 d1029e94 c045b937
[  122.362584]  c0c37f94 00000002 00000950 f9b313d4 00000d59 f9b2ebf0 f9b2ebf0 fffffff0
[  122.362600]  00000003 deb53d00 d1029ea4 c045ba42 00000009 00000000 d1029f08 f9b2ebf0
[  122.362617] Call Trace:
[  122.362633]  [<c0a86e54>] dump_stack+0x41/0x52
[  122.362645]  [<c045b937>] warn_slowpath_common+0x87/0xc0
[  122.362658]  [<f9b2ebf0>] ? ffs_ep0_write+0x730/0x810 [usb_f_fs]
[  122.362668]  [<f9b2ebf0>] ? ffs_ep0_write+0x730/0x810 [usb_f_fs]
[  122.362678]  [<c045ba42>] warn_slowpath_null+0x22/0x30
[  122.362689]  [<f9b2ebf0>] ffs_ep0_write+0x730/0x810 [usb_f_fs]
[  122.362702]  [<f9b2e4c0>] ? ffs_ep0_read+0x380/0x380 [usb_f_fs]
[  122.362712]  [<c05a1c1f>] __vfs_write+0x2f/0x100
[  122.362722]  [<c05a42f2>] ? __sb_start_write+0x52/0x110
[  122.362731]  [<c05a2534>] vfs_write+0x94/0x1b0
[  122.362740]  [<c0a8a1c0>] ? mutex_lock+0x10/0x30
[  122.362749]  [<c05a2f41>] SyS_write+0x51/0xb0
[  122.362759]  [<c0a8c71f>] sysenter_do_call+0x12/0x12
[  122.362766] ---[ end trace 0673d3467cecf8db ]---

in some cases (reproduction path below). This commit get back
semantic of that flag and ensures that ffs_closed() is called
always when needed but ffs_closed_callback() is called only
if this flag is set.

Reproduction path:
Compile kernel without any UDC driver or bound some gadget
to existing one and then:

$ modprobe g_ffs
$ mount none -t functionfs mount_point
$ ffs-example mount_point

This will fail with -ENODEV as there is no udc.

$ ffs-example mount_point

This will fail with -EBUSY because ffs_data has not been
properly cleaned up.

Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/function/f_fs.c

@@ -315,7 +315,6 @@ static ssize_t ffs_ep0_write(struct file *file, const char __user *buf,
 				return ret;
 			}
 
-			set_bit(FFS_FL_CALL_CLOSED_CALLBACK, &ffs->flags);
 			return len;
 		}
 		break;
@@ -1463,8 +1462,7 @@ static void ffs_data_clear(struct ffs_data *ffs)
 {
 	ENTER();
 
-	if (test_and_clear_bit(FFS_FL_CALL_CLOSED_CALLBACK, &ffs->flags))
-		ffs_closed(ffs);
+	ffs_closed(ffs);
 
 	BUG_ON(ffs->gadget);
 
@@ -3422,9 +3420,13 @@ static int ffs_ready(struct ffs_data *ffs)
 	ffs_obj->desc_ready = true;
 	ffs_obj->ffs_data = ffs;
 
-	if (ffs_obj->ffs_ready_callback)
+	if (ffs_obj->ffs_ready_callback) {
 		ret = ffs_obj->ffs_ready_callback(ffs);
+		if (ret)
+			goto done;
+	}
 
+	set_bit(FFS_FL_CALL_CLOSED_CALLBACK, &ffs->flags);
 done:
 	ffs_dev_unlock();
 	return ret;
@@ -3443,7 +3445,8 @@ static void ffs_closed(struct ffs_data *ffs)
 
 	ffs_obj->desc_ready = false;
 
-	if (ffs_obj->ffs_closed_callback)
+	if (test_and_clear_bit(FFS_FL_CALL_CLOSED_CALLBACK, &ffs->flags) &&
+	    ffs_obj->ffs_closed_callback)
 		ffs_obj->ffs_closed_callback(ffs);
 
 	if (!ffs_obj->opts || ffs_obj->opts->no_configfs