On 09/06/2012 12:58 PM, Bart Van Assche wrote: > _suOn 09/06/12 18:27, Michael Christie wrote: >> On Sep 3, 2012, at 9:12 AM, Bart Van Assche <bvanassche@xxxxxxx> wrote: >>> If the put_device() call in scsi_request_fn() drops the sdev refcount >>> to zero then the spin_lock() call after the put_device() call triggers >>> a use-after-free. Avoid that by making sure that blk_cleanup_queue() >>> can only finish after all active scsi_request_fn() calls have returned. >> >> If we have this patch http://marc.info/?l=linux-scsi&m=134453905402413&w=2 >> it seems we have all the scsi layer callers of the request_fn/ >> *blk_run_queue holding a reference to the device when they make the call. >> Right, or are there some other places missing? >> >> What are the other places we can call the request_fn without already >> holding a reference to the device? Is it the block layer? Is that why we >> need this patch? > > Hello Mike, > > The purpose of this patch is indeed to make *blk_run_queue() calls from > the block layer safe. There are several direct or indirect > *blk_run_queue() calls in the block layer where a reference on the queue > is held but not on the sdev, e.g. in the md, dm and bsg drivers. > Is there a race still? If some blk code is calling blk_run_queue (waiting on the queue lock) but no IO is queued, blk_drain_queue/blk_cleanup_queue could complete since the drain counters are zero. Then blk_run_queue could grab the queue lock and call the request_fn on a freed scsi_device (sdev pointed to by q->queuedata would be freed so scsi_reuqest_fn would be freed). Do we need a check in __blk_run_queue for QUEUE_FLAG_DEAD (if dead then fail IO?), or do we need a check in scsi_request_fn for this. A dead queue check or maybe null q->queuedata in scsi_device_dev_release_usercontext (do this with the queue lock held), then check for null q->queuedata in scsi_request_fn? -- 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
