[PATCH 4.19 41/67] usb: gadget: f_fs: Ensure io_completion_wq is idle during unbind

[Greg Kroah-Hartman]

From: Wesley Cheng <wcheng@xxxxxxxxxxxxxx>

commit 6fc1db5e6211e30fbb1cee8d7925d79d4ed2ae14 upstream.

During unbind, ffs_func_eps_disable() will be executed, resulting in
completion callbacks for any pending USB requests.  When using AIO,
irrespective of the completion status, io_data work is queued to
io_completion_wq to evaluate and handle the completed requests.  Since
work runs asynchronously to the unbind() routine, there can be a
scenario where the work runs after the USB gadget has been fully
removed, resulting in accessing of a resource which has been already
freed. (i.e. usb_ep_free_request() accessing the USB ep structure)

Explicitly drain the io_completion_wq, instead of relying on the
destroy_workqueue() (in ffs_data_put()) to make sure no pending
completion work items are running.

Signed-off-by: Wesley Cheng <wcheng@xxxxxxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/1621644261-1236-1-git-send-email-wcheng@xxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/usb/gadget/function/f_fs.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -3469,6 +3469,9 @@ static void ffs_func_unbind(struct usb_c
 		ffs->func = NULL;
 	}
 
+	/* Drain any pending AIO completions */
+	drain_workqueue(ffs->io_completion_wq);
+
 	if (!--opts->refcnt)
 		functionfs_unbind(ffs);