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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>
This commit is contained in:
Jan Höppner 2016-10-13 13:31:39 +02:00 committed by Martin Schwidefsky
parent 9de67725c8
commit 9f9d53e5bd
1 changed files with 15 additions and 2 deletions
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17
drivers/s390/block/dasd_devmap.c
View File

@ -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)
set_disk_ro(device->block->gdp, val);
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;