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    Subject[PATCH 1/5] Driver core: driver_find() drops reference before returning
    As part of the removal of get_driver()/put_driver(), this patch
    (as1510) changes driver_find(); it now drops the reference it acquires
    before returning. The patch also adjusts all the callers of
    driver_find() to remove the now unnecessary calls to put_driver().

    In addition, the patch adds a warning to driver_find(): Callers must
    make sure the driver they are searching for does not get unloaded
    while they are using it. This has always been the case; driver_find()
    has never prevented a driver from being unregistered or unloaded.
    Hence the patch will not introduce any new bugs. The existing callers
    all seem to be okay in this respect, however I don't understand the
    video drivers well enough to be certain about them.

    Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
    CC: Dmitry Torokhov <dmitry.torokhov@gmail.com>
    CC: Kyungmin Park <kyungmin.park@samsung.com>
    CC: Andy Walls <awalls@md.metrocast.net>
    CC: Martin Schwidefsky <schwidefsky@de.ibm.com>

    ---

    drivers/base/driver.c | 7 +++++--
    drivers/input/gameport/gameport.c | 1 -
    drivers/input/serio/serio.c | 1 -
    drivers/media/video/cx18/cx18-alsa-main.c | 1 -
    drivers/media/video/ivtv/ivtvfb.c | 2 --
    drivers/media/video/s5p-fimc/fimc-mdevice.c | 5 +----
    drivers/media/video/s5p-tv/mixer_video.c | 1 -
    drivers/s390/net/smsgiucv_app.c | 9 ++++-----
    8 files changed, 10 insertions(+), 17 deletions(-)

    Index: usb-3.3/drivers/base/driver.c
    ===================================================================
    --- usb-3.3.orig/drivers/base/driver.c
    +++ usb-3.3/drivers/base/driver.c
    @@ -234,7 +234,6 @@ int driver_register(struct device_driver

    other = driver_find(drv->name, drv->bus);
    if (other) {
    - put_driver(other);
    printk(KERN_ERR "Error: Driver '%s' is already registered, "
    "aborting...\n", drv->name);
    return -EBUSY;
    @@ -275,7 +274,9 @@ EXPORT_SYMBOL_GPL(driver_unregister);
    * Call kset_find_obj() to iterate over list of drivers on
    * a bus to find driver by name. Return driver if found.
    *
    - * Note that kset_find_obj increments driver's reference count.
    + * This routine provides no locking to prevent the driver it returns
    + * from being unregistered or unloaded while the caller is using it.
    + * The caller is responsible for preventing this.
    */
    struct device_driver *driver_find(const char *name, struct bus_type *bus)
    {
    @@ -283,6 +284,8 @@ struct device_driver *driver_find(const
    struct driver_private *priv;

    if (k) {
    + /* Drop reference added by kset_find_obj() */
    + kobject_put(k);
    priv = to_driver(k);
    return priv->driver;
    }
    Index: usb-3.3/drivers/input/gameport/gameport.c
    ===================================================================
    --- usb-3.3.orig/drivers/input/gameport/gameport.c
    +++ usb-3.3/drivers/input/gameport/gameport.c
    @@ -449,7 +449,6 @@ static ssize_t gameport_rebind_driver(st
    } else if ((drv = driver_find(buf, &gameport_bus)) != NULL) {
    gameport_disconnect_port(gameport);
    error = gameport_bind_driver(gameport, to_gameport_driver(drv));
    - put_driver(drv);
    } else {
    error = -EINVAL;
    }
    Index: usb-3.3/drivers/input/serio/serio.c
    ===================================================================
    --- usb-3.3.orig/drivers/input/serio/serio.c
    +++ usb-3.3/drivers/input/serio/serio.c
    @@ -441,7 +441,6 @@ static ssize_t serio_rebind_driver(struc
    } else if ((drv = driver_find(buf, &serio_bus)) != NULL) {
    serio_disconnect_port(serio);
    error = serio_bind_driver(serio, to_serio_driver(drv));
    - put_driver(drv);
    serio_remove_duplicate_events(serio, SERIO_RESCAN_PORT);
    } else {
    error = -EINVAL;
    Index: usb-3.3/drivers/media/video/cx18/cx18-alsa-main.c
    ===================================================================
    --- usb-3.3.orig/drivers/media/video/cx18/cx18-alsa-main.c
    +++ usb-3.3/drivers/media/video/cx18/cx18-alsa-main.c
    @@ -285,7 +285,6 @@ static void __exit cx18_alsa_exit(void)

    drv = driver_find("cx18", &pci_bus_type);
    ret = driver_for_each_device(drv, NULL, NULL, cx18_alsa_exit_callback);
    - put_driver(drv);

    cx18_ext_init = NULL;
    printk(KERN_INFO "cx18-alsa: module unload complete\n");
    Index: usb-3.3/drivers/media/video/ivtv/ivtvfb.c
    ===================================================================
    --- usb-3.3.orig/drivers/media/video/ivtv/ivtvfb.c
    +++ usb-3.3/drivers/media/video/ivtv/ivtvfb.c
    @@ -1293,7 +1293,6 @@ static int __init ivtvfb_init(void)

    drv = driver_find("ivtv", &pci_bus_type);
    err = driver_for_each_device(drv, NULL, &registered, ivtvfb_callback_init);
    - put_driver(drv);
    if (!registered) {
    printk(KERN_ERR "ivtvfb: no cards found\n");
    return -ENODEV;
    @@ -1310,7 +1309,6 @@ static void ivtvfb_cleanup(void)

    drv = driver_find("ivtv", &pci_bus_type);
    err = driver_for_each_device(drv, NULL, NULL, ivtvfb_callback_cleanup);
    - put_driver(drv);
    }

    module_init(ivtvfb_init);
    Index: usb-3.3/drivers/media/video/s5p-fimc/fimc-mdevice.c
    ===================================================================
    --- usb-3.3.orig/drivers/media/video/s5p-fimc/fimc-mdevice.c
    +++ usb-3.3/drivers/media/video/s5p-fimc/fimc-mdevice.c
    @@ -344,16 +344,13 @@ static int fimc_md_register_platform_ent
    return -ENODEV;
    ret = driver_for_each_device(driver, NULL, fmd,
    fimc_register_callback);
    - put_driver(driver);
    if (ret)
    return ret;

    driver = driver_find(CSIS_DRIVER_NAME, &platform_bus_type);
    - if (driver) {
    + if (driver)
    ret = driver_for_each_device(driver, NULL, fmd,
    csis_register_callback);
    - put_driver(driver);
    - }
    return ret;
    }

    Index: usb-3.3/drivers/media/video/s5p-tv/mixer_video.c
    ===================================================================
    --- usb-3.3.orig/drivers/media/video/s5p-tv/mixer_video.c
    +++ usb-3.3/drivers/media/video/s5p-tv/mixer_video.c
    @@ -58,7 +58,6 @@ static struct v4l2_subdev *find_and_regi
    }

    done:
    - put_driver(drv);
    return sd;
    }

    Index: usb-3.3/drivers/s390/net/smsgiucv_app.c
    ===================================================================
    --- usb-3.3.orig/drivers/s390/net/smsgiucv_app.c
    +++ usb-3.3/drivers/s390/net/smsgiucv_app.c
    @@ -168,7 +168,7 @@ static int __init smsgiucv_app_init(void
    rc = dev_set_name(smsg_app_dev, KMSG_COMPONENT);
    if (rc) {
    kfree(smsg_app_dev);
    - goto fail_put_driver;
    + goto fail;
    }
    smsg_app_dev->bus = &iucv_bus;
    smsg_app_dev->parent = iucv_root;
    @@ -177,7 +177,7 @@ static int __init smsgiucv_app_init(void
    rc = device_register(smsg_app_dev);
    if (rc) {
    put_device(smsg_app_dev);
    - goto fail_put_driver;
    + goto fail;
    }

    /* convert sender to uppercase characters */
    @@ -191,12 +191,11 @@ static int __init smsgiucv_app_init(void
    rc = smsg_register_callback(SMSG_PREFIX, smsg_app_callback);
    if (rc) {
    device_unregister(smsg_app_dev);
    - goto fail_put_driver;
    + goto fail;
    }

    rc = 0;
    -fail_put_driver:
    - put_driver(smsgiucv_drv);
    +fail:
    return rc;
    }
    module_init(smsgiucv_app_init);


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