[PATCH 1/1] usb: misc: usbtest: add fix for driver hang

[Lu Baolu]

In sg_timeout(), req->status is set to "-ETIMEDOUT" before calling
into usb_sg_cancel(). usb_sg_cancel() will do nothing and return
directly if req->status has been set to a non-zero value. This will
cause driver hang as soon as transfer time out is triggered.

In my test case, below system log shows when port reset happens after
urb being submitted.

[55099.746213] usb 2-3: USB disconnect, device number 2
[55321.955451] INFO: task kworker/6:0:59 blocked for more than 120 seconds.
[55321.955463]       Not tainted 4.7.0-rc6+ #19
[55321.955466] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[55321.955472] kworker/6:0     D ffff88045ad3bbf8     0    59      2 0x00000000
[55321.955489] Workqueue: usb_hub_wq hub_event
[55321.955493]  ffff88045ad3bbf8 ffff880400000030 ffff88045ad30f40 ffff88045ad3bbd0
[55321.955499]  ffff88045ad3c000 ffff8804590920fc ffff88045ad30f40 00000000ffffffff
[55321.955505]  ffff880459092100 ffff88045ad3bc10 ffffffff817b5925 ffff8804590920f8
[55321.955511] Call Trace:
[55321.955521]  [<ffffffff817b5925>] schedule+0x35/0x80
[55321.955527]  [<ffffffff817b5c1e>] schedule_preempt_disabled+0xe/0x10
[55321.955533]  [<ffffffff817b7505>] __mutex_lock_slowpath+0x95/0x110
[55321.955538]  [<ffffffff817b759f>] mutex_lock+0x1f/0x2f
[55321.955544]  [<ffffffff815b28a3>] usb_disconnect+0x53/0x270
[55321.955550]  [<ffffffff815b4521>] hub_port_connect+0x71/0x900
[55321.955556]  [<ffffffff815b08be>] ? hub_port_reset+0x3de/0x630
[55321.955562]  [<ffffffff815b53ee>] hub_event+0x63e/0xb20
[55321.955569]  [<ffffffff810ae675>] ? put_prev_entity+0x35/0x730
[55321.955577]  [<ffffffff810921f3>] process_one_work+0x153/0x3f0
[55321.955583]  [<ffffffff810929ab>] worker_thread+0x12b/0x4b0
[55321.955590]  [<ffffffff81092880>] ? rescuer_thread+0x340/0x340
[55321.955595]  [<ffffffff810981c9>] kthread+0xc9/0xe0
[55321.955601]  [<ffffffff817b961f>] ret_from_fork+0x1f/0x40
[55321.955606]  [<ffffffff81098100>] ? kthread_park+0x60/0x60
[55321.955638] INFO: task testusb:3011 blocked for more than 120 seconds.
[55321.955643]       Not tainted 4.7.0-rc6+ #19
[55321.955647] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[55321.955651] testusb         D ffff880449a079f8     0  3011   2367 0x00000000
[55321.955657]  ffff880449a079f8 0000000000000002 ffff88045754cc40 ffffffff815b91b9
[55321.955663]  ffff880449a08000 7fffffffffffffff ffff880449a07cb0 ffff88045754cc40
[55321.955668]  0000000000000000 ffff880449a07a10 ffffffff817b5925 ffff880449a07cb8
[55321.955673] Call Trace:
[55321.955680]  [<ffffffff815b91b9>] ? usb_hcd_submit_urb+0xa9/0xba0
[55321.955685]  [<ffffffff817b5925>] schedule+0x35/0x80
[55321.955691]  [<ffffffff817b8661>] schedule_timeout+0x231/0x2d0
[55321.955698]  [<ffffffff8117a592>] ? __alloc_pages_nodemask+0x112/0x2b0
[55321.955703]  [<ffffffff817b62e4>] wait_for_completion+0xa4/0x110
[55321.955709]  [<ffffffff810a2cb0>] ? wake_up_q+0x80/0x80
[55321.955713]  [<ffffffff815bcf78>] usb_sg_wait+0x138/0x190
[55321.955722]  [<ffffffffc01b6fdf>] perform_sglist+0xef/0x180 [usbtest]
[55321.955728]  [<ffffffffc01b6020>] ? usbtest_resume+0x10/0x10 [usbtest]
[55321.955734]  [<ffffffffc01b9648>] usbtest_do_ioctl+0x898/0x1520 [usbtest]
[55321.955740]  [<ffffffff815ba2a5>] ? usb_hcd_reset_endpoint+0x25/0x60
[55321.955745]  [<ffffffff815bd4f5>] ? usb_enable_endpoint+0x85/0x90
[55321.955751]  [<ffffffffc01ba3f3>] usbtest_ioctl+0x123/0x26e [usbtest]
[55321.955756]  [<ffffffff81172335>] ? filemap_map_pages+0x295/0x310
[55321.955763]  [<ffffffff815c5cc8>] ? proc_ioctl+0x48/0x210
[55321.955769]  [<ffffffff815c5db0>] proc_ioctl+0x130/0x210
[55321.955776]  [<ffffffff815c7d4a>] usbdev_do_ioctl+0x50a/0x1170
[55321.955782]  [<ffffffff815c89de>] usbdev_ioctl+0xe/0x20
[55321.955789]  [<ffffffff81207786>] do_vfs_ioctl+0x96/0x590
[55321.955794]  [<ffffffff81203723>] ? putname+0x53/0x60
[55321.955800]  [<ffffffff81207cf9>] SyS_ioctl+0x79/0x90
[55321.955806]  [<ffffffff817b93f6>] entry_SYSCALL_64_fastpath+0x1e/0xa

This patch fixes this driver hang. It should be back-ported to stable
kernel with version after v3.15.

Cc: stable@xxxxxxxxxxxxxxx
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
 drivers/usb/misc/usbtest.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/usb/misc/usbtest.c b/drivers/usb/misc/usbtest.c
index 6b978f0..6c6586d 100644
--- a/drivers/usb/misc/usbtest.c
+++ b/drivers/usb/misc/usbtest.c
@@ -585,7 +585,6 @@ static void sg_timeout(unsigned long _req)
 {
 	struct usb_sg_request	*req = (struct usb_sg_request *) _req;
 
-	req->status = -ETIMEDOUT;
 	usb_sg_cancel(req);
 }
 
-- 
2.1.4