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s390/cio: introduce locking for register/unregister functions
Unbinding an I/O subchannel with a child-CCW device in disconnected state sometimes causes a kernel-panic. The race condition was seen mostly during testing, when setting all the CHPIDs of a device to offline and at the same time, the unbinding the I/O subchannel driver. The kernel-panic occurs because of double delete, the I/O subchannel driver calls device_del on the CCW device while another device_del invocation for the same device is in-flight. For instance, disabling all the CHPIDs will trigger the ccw_device_remove function, which will call a ccw_device_unregister(), which ends up calling the device_del() which is asynchronous via cdev's todo workqueue. And unbinding the I/O subchannel driver calls io_subchannel_remove() function which calls the ccw_device_unregister() and device_del(). This double delete can be prevented by serializing all CCW device registration/unregistration calls into the driver core. This patch introduces a mutex which will be used for this purpose. Signed-off-by: Vineeth Vijayan <vneethv@linux.ibm.com> Reported-by: Boris Fiuczynski <fiuczy@linux.ibm.com> Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
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2 changed files with 11 additions and 0 deletions
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@ -15,6 +15,7 @@
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#include <asm/fcx.h>
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#include <asm/irq.h>
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#include <asm/schid.h>
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#include <linux/mutex.h>
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/* structs from asm/cio.h */
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struct irb;
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@ -87,6 +88,7 @@ struct ccw_device {
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spinlock_t *ccwlock;
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/* private: */
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struct ccw_device_private *private; /* cio private information */
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struct mutex reg_mutex;
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/* public: */
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struct ccw_device_id id;
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struct ccw_driver *drv;
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@ -244,10 +244,13 @@ int ccw_device_is_orphan(struct ccw_device *cdev)
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static void ccw_device_unregister(struct ccw_device *cdev)
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{
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mutex_lock(&cdev->reg_mutex);
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if (device_is_registered(&cdev->dev)) {
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/* Undo device_add(). */
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device_del(&cdev->dev);
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}
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mutex_unlock(&cdev->reg_mutex);
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if (cdev->private->flags.initialized) {
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cdev->private->flags.initialized = 0;
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/* Release reference from device_initialize(). */
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@ -653,11 +656,13 @@ static void ccw_device_do_unbind_bind(struct ccw_device *cdev)
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{
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int ret;
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mutex_lock(&cdev->reg_mutex);
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if (device_is_registered(&cdev->dev)) {
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device_release_driver(&cdev->dev);
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ret = device_attach(&cdev->dev);
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WARN_ON(ret == -ENODEV);
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}
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mutex_unlock(&cdev->reg_mutex);
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}
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static void
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@ -740,6 +745,7 @@ static int io_subchannel_initialize_dev(struct subchannel *sch,
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INIT_LIST_HEAD(&priv->cmb_list);
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init_waitqueue_head(&priv->wait_q);
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timer_setup(&priv->timer, ccw_device_timeout, 0);
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mutex_init(&cdev->reg_mutex);
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atomic_set(&priv->onoff, 0);
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cdev->ccwlock = sch->lock;
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@ -825,6 +831,7 @@ static void io_subchannel_register(struct ccw_device *cdev)
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* be registered). We need to reprobe since we may now have sense id
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* information.
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*/
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mutex_lock(&cdev->reg_mutex);
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if (device_is_registered(&cdev->dev)) {
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if (!cdev->drv) {
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ret = device_reprobe(&cdev->dev);
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@ -847,12 +854,14 @@ static void io_subchannel_register(struct ccw_device *cdev)
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spin_lock_irqsave(sch->lock, flags);
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sch_set_cdev(sch, NULL);
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spin_unlock_irqrestore(sch->lock, flags);
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mutex_unlock(&cdev->reg_mutex);
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/* Release initial device reference. */
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put_device(&cdev->dev);
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goto out_err;
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}
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out:
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cdev->private->flags.recog_done = 1;
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mutex_unlock(&cdev->reg_mutex);
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wake_up(&cdev->private->wait_q);
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out_err:
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if (adjust_init_count && atomic_dec_and_test(&ccw_device_init_count))
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