Commit 0e0d7520 authored Jul 29, 2014 by David Herrmann Committed by Jiri Kosina Aug 25, 2014

HID: uhid: simplify report-cb shutdown

The report-query is blocking, so when user-space destroys a device we have
to wake up any blocking kernel context that is currently in the report-cb.
We used some broken correlation between @report_done and @running so far.
Replace it by a much more obvious use.

We now wake up the report-cb if either @report_done or @running is set.
wake_up() and wait_event() serve as implicit barriers (as they always do)
so no need to use smp_rmb/wmb directly.

Note that @report_done is never reset by anyone but the report-cb, thus
it cannot flip twice while we wait for it. And whenever we set @running,
we afterwards synchronously remove the HID device. Therefore, we wait for
all report-cbs to finish before we return. This way, @running can never
flip to true while we wait for it.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

parent cee5aa1f

drivers/hid/uhid.c

+2 −9

Original line number	Diff line number	Diff line
		@@ -172,13 +172,9 @@ static int uhid_hid_get_raw(struct hid_device *hid, unsigned char rnum,
		spin_unlock_irqrestore(&uhid->qlock, flags);

		ret = wait_event_interruptible_timeout(uhid->report_wait,
		atomic_read(&uhid->report_done), 5 * HZ);
		atomic_read(&uhid->report_done) \|\| !uhid->running,
		5 * HZ);

		/*
		* Make sure "uhid->running" is cleared on shutdown before
		* "uhid->report_done" is set.
		*/
		smp_rmb();
		if (!ret \|\| !uhid->running) {
		ret = -EIO;
		} else if (ret < 0) {
		@@ -493,10 +489,7 @@ static int uhid_dev_destroy(struct uhid_device *uhid)
		if (!uhid->running)
		return -EINVAL;

		/* clear "running" before setting "report_done" */
		uhid->running = false;
		smp_wmb();
		atomic_set(&uhid->report_done, 1);
		wake_up_interruptible(&uhid->report_wait);

		hid_destroy_device(uhid->hid);