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[media] dvb_frontend: eliminate blocking wait in dvb_unregister_frontend()

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The wait_event() call in dvb_unregister_frontend() waits synchronously
for other tasks to free a file descriptor, but it does that while
holding several mutexes.  That alone is a bad idea, but if one user
process happens to keep a (defunct) file descriptor open indefinitely,
the kernel will correctly detect a hung task:

    INFO: task kworker/0:1:314 blocked for more than 30 seconds.
          Not tainted 4.7.0-rc1-hosting+ #50
    "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
    kworker/0:1     D ffff88003daf7a50     0   314      2 0x00000000
    Workqueue: usb_hub_wq hub_event
     ffff88003daf7a50 0000000000000296 ffff88003daf7a30 ffff88003fc13f98
     ffff88003dadce00 ffff88003daf8000 ffff88003e3fc010 ffff88003d48d4f8
     ffff88003e3b5030 ffff88003e3f8898 ffff88003daf7a68 ffffffff810cf860
    Call Trace:
     [<ffffffff810cf860>] schedule+0x30/0x80
     [<ffffffff812f88d3>] dvb_unregister_frontend+0x93/0xc0
     [<ffffffff8107a000>] ? __wake_up_common+0x80/0x80
     [<ffffffff813019c7>] dvb_usb_adapter_frontend_exit+0x37/0x70
     [<ffffffff81300614>] dvb_usb_exit+0x34/0xb0
     [<ffffffff81300d4a>] dvb_usb_device_exit+0x3a/0x50
     [<ffffffff81302dc2>] pctv452e_usb_disconnect+0x52/0x60
     [<ffffffff81295a07>] usb_unbind_interface+0x67/0x1e0
     [<ffffffff810609f3>] ? __blocking_notifier_call_chain+0x53/0x70
     [<ffffffff8127ba67>] __device_release_driver+0x77/0x110
     [<ffffffff8127c2d3>] device_release_driver+0x23/0x30
     [<ffffffff8127ab5d>] bus_remove_device+0x10d/0x150
     [<ffffffff8127879b>] device_del+0x13b/0x260
     [<ffffffff81299dea>] ? usb_remove_ep_devs+0x1a/0x30
     [<ffffffff8129468e>] usb_disable_device+0x9e/0x1e0
     [<ffffffff8128bb09>] usb_disconnect+0x89/0x260
     [<ffffffff8128db8d>] hub_event+0x30d/0xfc0
     [<ffffffff81059475>] process_one_work+0x1c5/0x4a0
     [<ffffffff8105940c>] ? process_one_work+0x15c/0x4a0
     [<ffffffff81059799>] worker_thread+0x49/0x480
     [<ffffffff81059750>] ? process_one_work+0x4a0/0x4a0
     [<ffffffff81059750>] ? process_one_work+0x4a0/0x4a0
     [<ffffffff8105f65e>] kthread+0xee/0x110
     [<ffffffff810400bf>] ret_from_fork+0x1f/0x40
     [<ffffffff8105f570>] ? __kthread_unpark+0x70/0x70
    5 locks held by kworker/0:1/314:
     #0:  ("usb_hub_wq"){......}, at: [<ffffffff8105940c>] process_one_work+0x15c/0x4a0
     #1:  ((&hub->events)){......}, at: [<ffffffff8105940c>] process_one_work+0x15c/0x4a0
     #2:  (&dev->mutex){......}, at: [<ffffffff8128d8cb>] hub_event+0x4b/0xfc0
     #3:  (&dev->mutex){......}, at: [<ffffffff8128bad2>] usb_disconnect+0x52/0x260
     #4:  (&dev->mutex){......}, at: [<ffffffff8127c2cb>] device_release_driver+0x1b/0x30

This patch removes the blocking wait, and postpones the kfree() call
until all file handles have been closed by using struct kref.

Signed-off-by: Max Kellermann <max@duempel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
This commit is contained in:
Max Kellermann 2016-07-04 09:08:51 -03:00 committed by Mauro Carvalho Chehab
parent a8e55d7e65
commit fe35637b0a
1 changed files with 25 additions and 8 deletions
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33
drivers/media/dvb-core/dvb_frontend.c
View File

@ -99,6 +99,7 @@ MODULE_PARM_DESC(dvb_mfe_wait_time, "Wait up to <mfe_wait_time> seconds on open(
static DEFINE_MUTEX(frontend_mutex);
struct dvb_frontend_private {
struct kref refcount;
/* thread/frontend values */
struct dvb_device *dvbdev;
@ -137,6 +138,23 @@ struct dvb_frontend_private {
#endif
};
static void dvb_frontend_private_free(struct kref *ref)
{
struct dvb_frontend_private *fepriv =
container_of(ref, struct dvb_frontend_private, refcount);
kfree(fepriv);
}
static void dvb_frontend_private_put(struct dvb_frontend_private *fepriv)
{
kref_put(&fepriv->refcount, dvb_frontend_private_free);
}
static void dvb_frontend_private_get(struct dvb_frontend_private *fepriv)
{
kref_get(&fepriv->refcount);
}
static void dvb_frontend_wakeup(struct dvb_frontend *fe);
static int dtv_get_frontend(struct dvb_frontend *fe,
struct dtv_frontend_properties *c,
@ -2543,6 +2561,8 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
fepriv->events.eventr = fepriv->events.eventw = 0;
}
dvb_frontend_private_get(fepriv);
if (adapter->mfe_shared)
mutex_unlock (&adapter->mfe_lock);
return ret;
@ -2591,6 +2611,8 @@ static int dvb_frontend_release(struct inode *inode, struct file *file)
fe->ops.ts_bus_ctrl(fe, 0);
}
dvb_frontend_private_put(fepriv);
return ret;
}
@ -2679,6 +2701,8 @@ int dvb_register_frontend(struct dvb_adapter* dvb,
}
fepriv = fe->frontend_priv;
kref_init(&fepriv->refcount);
sema_init(&fepriv->sem, 1);
init_waitqueue_head (&fepriv->wait_queue);
init_waitqueue_head (&fepriv->events.wait_queue);
@ -2713,18 +2737,11 @@ int dvb_unregister_frontend(struct dvb_frontend* fe)
mutex_lock(&frontend_mutex);
dvb_frontend_stop (fe);
mutex_unlock(&frontend_mutex);
if (fepriv->dvbdev->users < -1)
wait_event(fepriv->dvbdev->wait_queue,
fepriv->dvbdev->users==-1);
mutex_lock(&frontend_mutex);
dvb_unregister_device (fepriv->dvbdev);
/* fe is invalid now */
kfree(fepriv);
mutex_unlock(&frontend_mutex);
dvb_frontend_private_put(fepriv);
return 0;
}
EXPORT_SYMBOL(dvb_unregister_frontend);