USB: gadget: f_hid: fix deadlock in f_hidg_write()

In f_hidg_write() the write_spinlock is acquired before calling
usb_ep_queue() which causes a deadlock when dummy_hcd is being used.
This is because dummy_queue() callbacks into f_hidg_req_complete() which
tries to acquire the same spinlock. This is (part of) the backtrace when
the deadlock occurs:

  0xffffffffc06b1410 in f_hidg_req_complete
  0xffffffffc06a590a in usb_gadget_giveback_request
  0xffffffffc06cfff2 in dummy_queue
  0xffffffffc06a4b96 in usb_ep_queue
  0xffffffffc06b1eb6 in f_hidg_write
  0xffffffff8127730b in __vfs_write
  0xffffffff812774d1 in vfs_write
  0xffffffff81277725 in SYSC_write

Fix this by releasing the write_spinlock before calling usb_ep_queue()

Reviewed-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Tested-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: stable@vger.kernel.org # 4.11+
Fixes: 749494b6bdbb ("usb: gadget: f_hid: fix: Move IN request allocation to set_alt()")
Signed-off-by: Radoslav Gerganov <rgerganov@vmware.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/drivers/usb/gadget/function/f_hid.c b/drivers/usb/gadget/function/f_hid.c
index 75b113a5b25c..f3816a5c861e 100644
--- a/drivers/usb/gadget/function/f_hid.c
+++ b/drivers/usb/gadget/function/f_hid.c
@@ -391,20 +391,20 @@ try_again:
         req->complete = f_hidg_req_complete;
         req->context  = hidg;
 
+        spin_unlock_irqrestore(&hidg->write_spinlock, flags);
+
         status = usb_ep_queue(hidg->in_ep, req, GFP_ATOMIC);
         if (status < 0) {
                 ERROR(hidg->func.config->cdev,
                         "usb_ep_queue error on int endpoint %zd\n", status);
-                goto release_write_pending_unlocked;
+                goto release_write_pending;
         } else {
                 status = count;
         }
-        spin_unlock_irqrestore(&hidg->write_spinlock, flags);
 
         return status;
 release_write_pending:
         spin_lock_irqsave(&hidg->write_spinlock, flags);
-release_write_pending_unlocked:
         hidg->write_pending = 0;
         spin_unlock_irqrestore(&hidg->write_spinlock, flags);