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    Subject[120/146] [media] cx88: fix locking of sub-driver operations
    2.6.38-stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Jonathan Nieder <jrnieder@gmail.com>

    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>

    ---
    drivers/media/video/cx88/cx88-blackbird.c | 4 ++--
    drivers/media/video/cx88/cx88-dvb.c | 3 +--
    drivers/media/video/cx88/cx88-mpeg.c | 4 ----
    drivers/media/video/cx88/cx88.h | 3 ++-
    4 files changed, 5 insertions(+), 9 deletions(-)

    --- 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 *fil

    /* 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;
    }

    --- 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_

    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_
    dev->frontends.active_fe_id = 0;
    }
    }
    + mutex_unlock(&dev->core->lock);

    return ret;
    }
    --- 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

    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
    {
    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;
    }
    --- 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 */



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