[media] cx88: fix locking of sub-driver operations

The BKL conversion of this driver seems to have gone wrong.
Loading the cx88-blackbird driver deadlocks.

The cause: mpeg_ops::open in the cx2388x blackbird driver acquires the
device lock and calls the sub-driver's request_acquire, which tries to
acquire the lock again.  Fix it by clarifying the semantics of
request_acquire, request_release, advise_acquire, and advise_release:
now all will rely on the caller to acquire the device lock.

Based on work by Ben Hutchings <ben@decadent.org.uk>.

Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=31962

Reported-by: Andi Huber <hobrom@gmx.at>
Tested-by: Andi Huber <hobrom@gmx.at>
Tested-by: Marlon de Boer <marlon@hyves.nl>
Cc: stable@kernel.org
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 0 insertions, 4 deletions

diff --git a/drivers/media/video/cx88/cx88-mpeg.c b/drivers/media/video/cx88/cx88-mpeg.c
index a092c3a4c56d..91d3d179c3c7 100644
--- a/drivers/media/video/cx88/cx88-mpeg.c
+++ b/drivers/media/video/cx88/cx88-mpeg.c
@@ -624,13 +624,11 @@ static int cx8802_request_acquire(struct cx8802_driver *drv)
 
         if (drv->advise_acquire)
         {
-                mutex_lock(&drv->core->lock);
                 core->active_ref++;
                 if (core->active_type_id == CX88_BOARD_NONE) {
                         core->active_type_id = drv->type_id;
                         drv->advise_acquire(drv);
                 }
-                mutex_unlock(&drv->core->lock);
 
                 mpeg_dbg(1,"%s() Post acquire GPIO=%x\n", __func__, cx_read(MO_GP0_IO));
         }
@@ -643,14 +641,12 @@ static int cx8802_request_release(struct cx8802_driver *drv)
 {
         struct cx88_core *core = drv->core;
 
-        mutex_lock(&drv->core->lock);
         if (drv->advise_release && --core->active_ref == 0)
         {
                 drv->advise_release(drv);
                 core->active_type_id = CX88_BOARD_NONE;
                 mpeg_dbg(1,"%s() Post release GPIO=%x\n", __func__, cx_read(MO_GP0_IO));
         }
-        mutex_unlock(&drv->core->lock);
 
         return 0;
 }