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[S390] tape: Fix race condition in tape block device driver

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Due to incorrect function call sequence it can happen that a tape block
request is finished before the request is taken from the block request queue.

The following sequence leads to that condition:
 * tapeblock_start_request() -> start CCW program
 * Request finishes -> IO interrupt
 * tapeblock_end_request()
 * end_that_request_last()

If blkdev_dequeue_request() has not been called before end_that_request_last(),
a kernel bug is triggered in end_that_request_last() because the request is
still queued. To solve that problem blkdev_dequeue_request() has to be called
before starting the CCW program.

Signed-off-by: Michael Holzheu <holzheu@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Michael Holzheu 2008-05-30 10:03:25 +02:00 committed by Martin Schwidefsky
parent 97195d6b41
commit f71ad62a26
1 changed files with 2 additions and 2 deletions
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4
drivers/s390/char/tape_block.c
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@ -179,11 +179,11 @@ tapeblock_requeue(struct work_struct *work) {
tapeblock_end_request(req, -EIO);
continue;
}
blkdev_dequeue_request(req);
nr_queued++;
spin_unlock_irq(&device->blk_data.request_queue_lock);
rc = tapeblock_start_request(device, req);
spin_lock_irq(&device->blk_data.request_queue_lock);
blkdev_dequeue_request(req);
nr_queued++;
}
spin_unlock_irq(&device->blk_data.request_queue_lock);
atomic_set(&device->blk_data.requeue_scheduled, 0);