cx88: fix locking of sub-driver operations

BugLink: http://bugs.launchpad.net/bugs/793702

commit 1fe70e963028f34ba5e32488a7870ff4b410b19b upstream.

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>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

diff --git a/drivers/media/video/cx88/cx88-blackbird.c b/drivers/media/video/cx88/cx88-blackbird.c
index b93fbd3..a6f7d53 100644 (file)
--- a/drivers/media/video/cx88/cx88-blackbird.c
+++ b/drivers/media/video/cx88/cx88-blackbird.c
@@ -1125,13 +1125,13 @@ static int mpeg_release(struct file *file)
 
        /* Make sure we release the hardware */
        drv = cx8802_get_driver(dev, CX88_MPEG_BLACKBIRD);
-       mutex_unlock(&dev->core->lock);
-
        if (drv)
                drv->request_release(drv);
 
        atomic_dec(&dev->core->mpeg_users);
 
+       mutex_unlock(&dev->core->lock);
+
        return 0;
 }
 

diff --git a/drivers/media/video/cx88/cx88-dvb.c b/drivers/media/video/cx88/cx88-dvb.c
index 88a1507..5eccd02 100644 (file)
--- a/drivers/media/video/cx88/cx88-dvb.c
+++ b/drivers/media/video/cx88/cx88-dvb.c
@@ -134,8 +134,6 @@ static int cx88_dvb_bus_ctrl(struct dvb_frontend* fe, int acquire)
 
        mutex_lock(&dev->core->lock);
        drv = cx8802_get_driver(dev, CX88_MPEG_DVB);
-       mutex_unlock(&dev->core->lock);
-
        if (drv) {
                if (acquire){
                        dev->frontends.active_fe_id = fe_id;
@@ -145,6 +143,7 @@ static int cx88_dvb_bus_ctrl(struct dvb_frontend* fe, int acquire)
                        dev->frontends.active_fe_id = 0;
                }
        }
+       mutex_unlock(&dev->core->lock);
 
        return ret;
 }

diff --git a/drivers/media/video/cx88/cx88-mpeg.c b/drivers/media/video/cx88/cx88-mpeg.c
index 918172b..9147c16 100644 (file)
--- 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;
 }

diff --git a/drivers/media/video/cx88/cx88.h b/drivers/media/video/cx88/cx88.h
index 6ff34c7..e912919 100644 (file)
--- a/drivers/media/video/cx88/cx88.h
+++ b/drivers/media/video/cx88/cx88.h
@@ -500,7 +500,8 @@ struct cx8802_driver {
        /* Caller must _not_ hold core->lock */
        int (*probe)(struct cx8802_driver *drv);
 
-       /* Caller must hold core->lock */
+       /* Callers to the following functions must hold core->lock */
+
        int (*remove)(struct cx8802_driver *drv);
 
        /* MPEG 8802 -> mini driver - Access for hardware control */