[media] gspca: Don't set gspca_dev->dev to NULL before stop0

In commit a3d6e8cc0e6ddc8b3cfdeb3c979f07ed1aa528b3 gspca_dev->dev is set
to NULL on disconnect, before calling stop0. The plan was to get rid of
gspca_dev->present and instead simply check for gspca_dev->dev everywhere
where we were checking for present. This should be race free since all users
of gspca_dev->dev hold the usb_lock, or so I thought.

But I was wrong, drivers which use a work-queue + synchronous bulk transfers
to get the video data don't hold the usb_lock while doing so, their stop0
callbacks stop the workqueue, so they won't be using gspca_dev->dev anymore
after the stop0 call, but they might be dereferincing it before, so we should
not set gspca_dev->dev to NULL on disconnect before calling stop0.

This also means that the workqueue functions in these drivers cannot
use gspca_dev->dev to check if they need to stop because of disconnection,
so we will need to keep gspca_dev->present around, and set that to 0 on
disconnect, before calling stop0. Unfortunately as part of the plan to remove
gspca_dev->present, these workqueues where already moved over to checking
for gspca_dev->dev instead of gspca_dev->present as part of commit
254902b01d2acc6aced99ec17caa4c6cd890cdea, so this patch also reverts those
parts of that commit.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/media/usb/gspca/zc3xx.c b/drivers/media/usb/gspca/zc3xx.c
index f0bacee33ef9..234d9eaa8eea 100644
--- a/drivers/media/usb/gspca/zc3xx.c
+++ b/drivers/media/usb/gspca/zc3xx.c
@@ -5950,7 +5950,7 @@ static void transfer_update(struct work_struct *work)
                 if (gspca_dev->frozen)
                         goto err;
 #endif
-                if (!gspca_dev->dev || !gspca_dev->streaming)
+                if (!gspca_dev->present || !gspca_dev->streaming)
                         goto err;
 
                 /* Bit 0 of register 11 indicates FIFO overflow */
@@ -6842,7 +6842,7 @@ static void sd_stop0(struct gspca_dev *gspca_dev)
                 mutex_lock(&gspca_dev->usb_lock);
                 sd->work_thread = NULL;
         }
-        if (!gspca_dev->dev)
+        if (!gspca_dev->present)
                 return;
         send_unknown(gspca_dev, sd->sensor);
 }