On Thu, 2012-08-16 at 07:52 +0000, Bart Van Assche wrote: > On 08/16/12 01:35, Chanho Min wrote: > >> functions will occur in line. I also don't see why the sdev reference > >> couldn't drop to zero here. > > scsi_request_fn is called under the lock of request_queue->queue_lock. > > If we drop the sdev reference to zero here, > > scsi_device_dev_release_usercontext is > > invoked and make request_queue to NULL. When caller of scsi_request_fn try to > > unlock request_queue->queue_lock, the oops is occurred. > > Whether or not your patch is applied, if the put_device() call in > scsi_request_fn() decreases the sdev reference count to zero, the > scsi_request_fn() caller will still try to unlock the queue lock after > scsi_request_fn() finished and hence will trigger a use-after-free. I'm > afraid the only real solution is to modify the SCSI and/or block layers > such that scsi_remove_device() can't finish while scsi_request_fn() is > in progress. And once that is guaranteed the get_device() / put_device() > pair can be left out from scsi_request_fn(). Well, no. The only way to destroy a queue is with blk_cleanup_queue() which does the final put. blk_cleanup_queue has a rather clunky drain check that looks at both queued and in-flight requests. Even if we have a scsi_remove_device() racing with the scsi_request_fn() and it gets to blk_cleanup_queue(), that call gets held at the drain wait until the scsi_request_fn() has exited. The same is true for all other request functions, so we're safe. James -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
