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SubjectRe: [PATCH] USB: serial: mos7720: defer state restore to a workqueue
On Mon, 16 Nov 2020, Johan Hovold wrote:

>On Fri, Nov 13, 2020 at 08:27:25PM -0800, Davidlohr Bueso wrote:
>> @@ -1883,21 +1724,17 @@ static void mos7720_release(struct usb_serial *serial)
>> if (mos_parport->msg_pending)
>> wait_for_completion_timeout(&mos_parport->syncmsg_compl,
>> msecs_to_jiffies(MOS_WDR_TIMEOUT));
>> + /*
>> + * If delayed work is currently scheduled, wait for it to
>> + * complete. This also implies barriers that ensure the
>> + * below serial clearing is not hoisted above the ->work.
>> + */
>> + cancel_work_sync(&mos_parport->work);
>
>As I mentioned, this needs to be done *after* deregistering the port or
>you could theoretically end up with the work item being requeued.

Hmm sorry yes I forgot to mention this. I was counting on the private_data
already being null to prevent any new work being actually scheduled, so an
incoming restore state, for example, would be a nop.

>
>Yes, the same applies for the "synchronous" requests, but that's a
>preexisting issue.

Per the above I also assumed sync requests were also safe as is.

But I can certainly re-order things, how about:

mos7720_release():
mos_parport->pp->private_data = NULL;
parport_remove_port(mos_parport->pp);

wait_for_completion_timeout();
cancel_work_sync();

usb_set_serial_data(serial, NULL);
mos_parport->serial = NULL;

parport_del_port(mos_parport->pp);
kref_put();

Thanks,
Davidlohr

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