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>

1 files changed, 2 insertions, 9 deletions

diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
index 0cb92e347258..16af4d382391 100644
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -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);