FAILED: patch "[PATCH] USB: gadget: f_hid: fix deadlock in f_hidg_write()" failed to apply to 4.9-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 072684e8c58d17e853f8e8b9f6d9ce2e58d2b036 Mon Sep 17 00:00:00 2001
From: Radoslav Gerganov <rgerganov@xxxxxxxxxx>
Date: Tue, 5 Mar 2019 10:10:34 +0000
Subject: [PATCH] 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@xxxxxxxxxxxxxxxxxxxxx>
Tested-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 4.11+
Fixes: 749494b6bdbb ("usb: gadget: f_hid: fix: Move IN request allocation to set_alt()")
Signed-off-by: Radoslav Gerganov <rgerganov@xxxxxxxxxx>
Signed-off-by: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx>

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 @@ 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) {
 		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);