Re: Linux 3.0 oopses when pulling a USB CDROM

[Andi Kleen]

> 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.

-Andi
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