Commit 9f9d53e5 authored Oct 13, 2016 by Jan Höppner Committed by Martin Schwidefsky Oct 28, 2016

s390/dasd: Fix locking issue when changing RO attribute



The function dasd_ro_store() calls set_disk_ro() to set the device in
question read-only. Since set_disk_ro() might sleep, we can't call it
while holding a lock. However, we also can't simply check if the device,
block, and gdp references are valid before we call set_disk_ro() because
an offline processing might have been started in the meanwhile which
will destroy those references.

In order to reliably call set_disk_ro() we have to ensure several
things:

- Still check validity of the mentioned references but additionally
  check if offline processing is running and bail out accordingly. Also,
  do this while holding the device lock.
- To ensure that the block device is still safe after the lock, increase
  the open_count while still holding the device lock.

Reviewed-by: Stefan Haberland <sth@linux.vnet.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

parent 9de67725

drivers/s390/block/dasd_devmap.c

+15 −2

Original line number	Diff line number	Diff line
		@@ -761,6 +761,7 @@ dasd_ro_store(struct device dev, struct device_attribute attr,
		{
		struct ccw_device *cdev = to_ccwdev(dev);
		struct dasd_device *device;
		unsigned long flags;
		unsigned int val;
		int rc;

		@@ -775,10 +776,22 @@ dasd_ro_store(struct device dev, struct device_attribute attr,
		if (IS_ERR(device))
		return PTR_ERR(device);

		spin_lock_irqsave(get_ccwdev_lock(cdev), flags);
		val = val \|\| test_bit(DASD_FLAG_DEVICE_RO, &device->flags);
		if (device->block && device->block->gdp)

		if (!device->block \|\| !device->block->gdp \|\|
		test_bit(DASD_FLAG_OFFLINE, &device->flags)) {
		spin_unlock_irqrestore(get_ccwdev_lock(cdev), flags);
		goto out;
		}
		/* Increase open_count to avoid losing the block device */
		atomic_inc(&device->block->open_count);
		spin_unlock_irqrestore(get_ccwdev_lock(cdev), flags);

		set_disk_ro(device->block->gdp, val);
		atomic_dec(&device->block->open_count);

		out:
		dasd_put_device(device);

		return count;

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