usb: gadget: f_fs: Fix possibe deadlock

BugLink: http://bugs.launchpad.net/bugs/1702863

commit b3ce3ce upstream.

When system try to close /dev/usb-ffs/adb/ep0 on one core, at the same
time another core try to attach new UDC, which will cause deadlock as
below scenario. Thus we should release ffs lock before issuing
unregister_gadget_item().

[   52.642225] c1 ======================================================
[   52.642228] c1 [ INFO: possible circular locking dependency detected ]
[   52.642236] c1 4.4.6+ #1 Tainted: G        W  O
[   52.642241] c1 -------------------------------------------------------
[   52.642245] c1 usb ffs open/2808 is trying to acquire lock:
[   52.642270] c0  (udc_lock){+.+.+.}, at: [<ffffffc00065aeec>]
		usb_gadget_unregister_driver+0x3c/0xc8
[   52.642272] c1  but task is already holding lock:
[   52.642283] c0  (ffs_lock){+.+.+.}, at: [<ffffffc00066b244>]
		ffs_data_clear+0x30/0x140
[   52.642285] c1 which lock already depends on the new lock.
[   52.642287] c1
               the existing dependency chain (in reverse order) is:
[   52.642295] c0
	       -> #1 (ffs_lock){+.+.+.}:
[   52.642307] c0        [<ffffffc00012340c>] __lock_acquire+0x20f0/0x2238
[   52.642314] c0        [<ffffffc000123b54>] lock_acquire+0xe4/0x298
[   52.642322] c0        [<ffffffc000aaf6e8>] mutex_lock_nested+0x7c/0x3cc
[   52.642328] c0        [<ffffffc00066f7bc>] ffs_func_bind+0x504/0x6e8
[   52.642334] c0        [<ffffffc000654004>] usb_add_function+0x84/0x184
[   52.642340] c0        [<ffffffc000658ca4>] configfs_composite_bind+0x264/0x39c
[   52.642346] c0        [<ffffffc00065b348>] udc_bind_to_driver+0x58/0x11c
[   52.642352] c0        [<ffffffc00065b49c>] usb_udc_attach_driver+0x90/0xc8
[   52.642358] c0        [<ffffffc0006598e0>] gadget_dev_desc_UDC_store+0xd4/0x128
[   52.642369] c0        [<ffffffc0002c14e8>] configfs_write_file+0xd0/0x13c
[   52.642376] c0        [<ffffffc00023c054>] vfs_write+0xb8/0x214
[   52.642381] c0        [<ffffffc00023cad4>] SyS_write+0x54/0xb0
[   52.642388] c0        [<ffffffc000085ff0>] el0_svc_naked+0x24/0x28
[   52.642395] c0
              -> #0 (udc_lock){+.+.+.}:
[   52.642401] c0        [<ffffffc00011e3d0>] print_circular_bug+0x84/0x2e4
[   52.642407] c0        [<ffffffc000123454>] __lock_acquire+0x2138/0x2238
[   52.642412] c0        [<ffffffc000123b54>] lock_acquire+0xe4/0x298
[   52.642420] c0        [<ffffffc000aaf6e8>] mutex_lock_nested+0x7c/0x3cc
[   52.642427] c0        [<ffffffc00065aeec>] usb_gadget_unregister_driver+0x3c/0xc8
[   52.642432] c0        [<ffffffc00065995c>] unregister_gadget_item+0x28/0x44
[   52.642439] c0        [<ffffffc00066b34c>] ffs_data_clear+0x138/0x140
[   52.642444] c0        [<ffffffc00066b374>] ffs_data_reset+0x20/0x6c
[   52.642450] c0        [<ffffffc00066efd0>] ffs_data_closed+0xac/0x12c
[   52.642454] c0        [<ffffffc00066f070>] ffs_ep0_release+0x20/0x2c
[   52.642460] c0        [<ffffffc00023dbe4>] __fput+0xb0/0x1f4
[   52.642466] c0        [<ffffffc00023dd9c>] ____fput+0x20/0x2c
[   52.642473] c0        [<ffffffc0000ee944>] task_work_run+0xb4/0xe8
[   52.642482] c0        [<ffffffc0000cd45c>] do_exit+0x360/0xb9c
[   52.642487] c0        [<ffffffc0000cf228>] do_group_exit+0x4c/0xb0
[   52.642494] c0        [<ffffffc0000dd3c8>] get_signal+0x380/0x89c
[   52.642501] c0        [<ffffffc00008a8f0>] do_signal+0x154/0x518
[   52.642507] c0        [<ffffffc00008af00>] do_notify_resume+0x70/0x78
[   52.642512] c0        [<ffffffc000085ee8>] work_pending+0x1c/0x20
[   52.642514] c1
              other info that might help us debug this:
[   52.642517] c1  Possible unsafe locking scenario:
[   52.642518] c1        CPU0                    CPU1
[   52.642520] c1        ----                    ----
[   52.642525] c0   lock(ffs_lock);
[   52.642529] c0                                lock(udc_lock);
[   52.642533] c0                                lock(ffs_lock);
[   52.642537] c0   lock(udc_lock);
[   52.642539] c1
                      *** DEADLOCK ***
[   52.642543] c1 1 lock held by usb ffs open/2808:
[   52.642555] c0  #0:  (ffs_lock){+.+.+.}, at: [<ffffffc00066b244>]
		ffs_data_clear+0x30/0x140
[   52.642557] c1 stack backtrace:
[   52.642563] c1 CPU: 1 PID: 2808 Comm: usb ffs open Tainted: G
[   52.642565] c1 Hardware name: Spreadtrum SP9860g Board (DT)
[   52.642568] c1 Call trace:
[   52.642573] c1 [<ffffffc00008b430>] dump_backtrace+0x0/0x170
[   52.642577] c1 [<ffffffc00008b5c0>] show_stack+0x20/0x28
[   52.642583] c1 [<ffffffc000422694>] dump_stack+0xa8/0xe0
[   52.642587] c1 [<ffffffc00011e548>] print_circular_bug+0x1fc/0x2e4
[   52.642591] c1 [<ffffffc000123454>] __lock_acquire+0x2138/0x2238
[   52.642595] c1 [<ffffffc000123b54>] lock_acquire+0xe4/0x298
[   52.642599] c1 [<ffffffc000aaf6e8>] mutex_lock_nested+0x7c/0x3cc
[   52.642604] c1 [<ffffffc00065aeec>] usb_gadget_unregister_driver+0x3c/0xc8
[   52.642608] c1 [<ffffffc00065995c>] unregister_gadget_item+0x28/0x44
[   52.642613] c1 [<ffffffc00066b34c>] ffs_data_clear+0x138/0x140
[   52.642618] c1 [<ffffffc00066b374>] ffs_data_reset+0x20/0x6c
[   52.642621] c1 [<ffffffc00066efd0>] ffs_data_closed+0xac/0x12c
[   52.642625] c1 [<ffffffc00066f070>] ffs_ep0_release+0x20/0x2c
[   52.642629] c1 [<ffffffc00023dbe4>] __fput+0xb0/0x1f4
[   52.642633] c1 [<ffffffc00023dd9c>] ____fput+0x20/0x2c
[   52.642636] c1 [<ffffffc0000ee944>] task_work_run+0xb4/0xe8
[   52.642640] c1 [<ffffffc0000cd45c>] do_exit+0x360/0xb9c
[   52.642644] c1 [<ffffffc0000cf228>] do_group_exit+0x4c/0xb0
[   52.642647] c1 [<ffffffc0000dd3c8>] get_signal+0x380/0x89c
[   52.642651] c1 [<ffffffc00008a8f0>] do_signal+0x154/0x518
[   52.642656] c1 [<ffffffc00008af00>] do_notify_resume+0x70/0x78
[   52.642659] c1 [<ffffffc000085ee8>] work_pending+0x1c/0x20

Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Cc: Jerry Zhang <zhangjerry@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

drivers/usb/gadget/function/f_fs.c

@@ -3463,6 +3463,7 @@ static void ffs_closed(struct ffs_data *ffs)
 {
 	struct ffs_dev *ffs_obj;
 	struct f_fs_opts *opts;
+	struct config_item *ci;
 
 	ENTER();
 	ffs_dev_lock();
@@ -3486,8 +3487,11 @@ static void ffs_closed(struct ffs_data *ffs)
 	    || !atomic_read(&opts->func_inst.group.cg_item.ci_kref.refcount))
 		goto done;
 
-	unregister_gadget_item(ffs_obj->opts->
-			       func_inst.group.cg_item.ci_parent->ci_parent);
+	ci = opts->func_inst.group.cg_item.ci_parent->ci_parent;
+	ffs_dev_unlock();
+
+	unregister_gadget_item(ci);
+	return;
 done:
 	ffs_dev_unlock();
 }