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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 <>
Tested-by: James Bottomley <>
Cc: # 4.11+
Fixes: 749494b ("usb: gadget: f_hid: fix: Move IN request allocation to set_alt()")
Signed-off-by: Radoslav Gerganov <>
Signed-off-by: Felipe Balbi <>
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rgerganov authored and Felipe Balbi committed Mar 20, 2019
1 parent 091dacc commit 072684e8c58d17e853f8e8b9f6d9ce2e58d2b036
Showing with 3 additions and 3 deletions.
  1. +3 −3 drivers/usb/gadget/function/f_hid.c
@@ -391,20 +391,20 @@ static ssize_t f_hidg_write(struct file *file, const char __user *buffer,
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) {
"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;
spin_lock_irqsave(&hidg->write_spinlock, flags);
hidg->write_pending = 0;
spin_unlock_irqrestore(&hidg->write_spinlock, flags);

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