On 05/02/2012 04:25 PM, Stefan Bader wrote: > While looking at a bug report [1] I found that the immediate cause of the crash > was in that specific case the reference cp->cmd for a printk: > > /* > * The device didn't switch to MSG IN phase after > * having reselected the initiator. > */ > case SIR_RESEL_NO_MSG_IN: > scmd_printk(KERN_WARNING, cp->cmd, > "No MSG IN phase after reselection\n"); > goto out_stuck; > > Unfortunately cp (that is returned by sym_ccb_from_dsa()) is NULL. This probably > is as old as 2.6.24 when this patch added the scmd_printk: > > commit 3fb364e089e05c35ead55a08d56d3004193681f6 > Author: Matthew Wilcox <matthew@xxxxxx> > Date: Fri Oct 5 15:55:10 2007 -0400 > > [SCSI] sym53c8xx: Use scmd_printk where appropriate > > A quick research looks like it might be other cases where this happened[2]. > Maybe more often (or solely?) when running in a VM (KVM). I even found some post > that looks like it tries to fix just this problem[3]. > > However without more knowledge about that driver it could also be a problem in > the hardware emulation so that normally cp == NULL should never happen. Or it > might be that the emulation is just running sufficiently "different" to cause > races to happen which never would be observed on real hardware. > > Would [3] still make sense? > cp->cmd == NULL would point to a race with SCSI command completion, basically the same issue USB is facing right now. So yes, it can happen (as you've seen), so I would got for [3]. And if only to avoid the Oops and figure out what _really_ went wrong here. Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg) -- 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
