On Sat, 2 Jul 2011, Andi Kleen wrote: > > The problem is that blk_peek_request() calls scsi_prep_fn(), which > > does this: > > > > struct scsi_device *sdev = q->queuedata; > > int ret = BLKPREP_KILL; > > > > if (req->cmd_type == REQ_TYPE_BLOCK_PC) > > ret = scsi_setup_blk_pc_cmnd(sdev, req); > > return scsi_prep_return(q, req, ret); > > > > It doesn't check to see if sdev is NULL, nor does > > scsi_setup_blk_pc_cmnd(). That accounts for this error: > > I actually added a NULL check in scsi_setup_blk_pc_cmnd early on, > but that just caused RCU CPU stalls afterwards and then eventually > a hung system. The RCU problem is likely to be a separate issue. It might even be a result of the use-after-free problem with the elevator. At any rate, it's clear that the crash in the refcounting log you posted occurred because scsi_setup_blk_pc_cmnd() called scsi_prep_state_check(), which tried to dereference the NULL pointer. Would you like to try this patch to see if it fixes the problem? As I said before, I'm not certain it's the best thing to do, but it worked on my system. Alan Stern Index: usb-3.0/drivers/scsi/scsi_lib.c =================================================================== --- usb-3.0.orig/drivers/scsi/scsi_lib.c +++ usb-3.0/drivers/scsi/scsi_lib.c @@ -1247,6 +1247,8 @@ int scsi_prep_fn(struct request_queue *q struct scsi_device *sdev = q->queuedata; int ret = BLKPREP_KILL; + if (!sdev) + return ret; if (req->cmd_type == REQ_TYPE_BLOCK_PC) ret = scsi_setup_blk_pc_cmnd(sdev, req); return scsi_prep_return(q, req, ret); Index: usb-3.0/drivers/scsi/scsi_sysfs.c =================================================================== --- usb-3.0.orig/drivers/scsi/scsi_sysfs.c +++ usb-3.0/drivers/scsi/scsi_sysfs.c @@ -322,6 +322,8 @@ static void scsi_device_dev_release_user kfree(evt); } + /* Freeing the queue signals to block that we're done */ + scsi_free_queue(sdev->request_queue); blk_put_queue(sdev->request_queue); /* NULL queue means the device can't be used */ sdev->request_queue = NULL; @@ -936,8 +938,6 @@ void __scsi_remove_device(struct scsi_de /* cause the request function to reject all I/O requests */ sdev->request_queue->queuedata = NULL; - /* Freeing the queue signals to block that we're done */ - scsi_free_queue(sdev->request_queue); put_device(dev); } -- 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
