Re: [PATCH 1/1] megaraid_{mm,mbox}: fix a bug in reset handler

[Andre Hedrick]

Andrew,

This is real, and is a known bug which is 100% reproducable (sp).
There are other harry issues too, but this is as much as I can say.

cpu_relax() will not work, already tried some time ago.


Andre Hedrick
LAD Storage Consulting Group

On Wed, 12 Apr 2006, Andrew Morton wrote:

> "Ju, Seokmann" <Seokmann.Ju@xxxxxxxx> wrote:
> >
> > This patch has fix for a bug in the 'megaraid_reset_handler()'.
> > 
> >  When abort failed, the driver gets reset handleer called. In the reset
> >  handler, driver calls 'scsi_done()' callback for same SCSI command
> >  packet (struct scsi_cmnd) multiple times if there are multiple SCSI
> >  command packet in the pend_list. More over, if there are entry in the
> >  pend_lsit with IOCTL packet associated, the driver returns it to wrong
> >  free_list so that, in turn, the driver could end up with 'NULL pointer
> >  dereference..' during I/O command building with incorrect resource.
> > 
> >  Also, the patch contains several minor/cosmetic changes besides this.
> >
> > ..
> >
> > @@ -2655,32 +2655,48 @@
> >  	// Also, reset all the commands currently owned by the driver
> >  	spin_lock_irqsave(PENDING_LIST_LOCK(adapter), flags);
> >  	list_for_each_entry_safe(scb, tmp, &adapter->pend_list, list) {
> > -
> >  		list_del_init(&scb->list);	// from pending list
> >  
> > -		con_log(CL_ANN, (KERN_WARNING
> > -			"megaraid: %ld:%d[%d:%d], reset from pending list\n",
> > -				scp->serial_number, scb->sno,
> > -				scb->dev_channel, scb->dev_target));
> > +		if (scb->sno >= MBOX_MAX_SCSI_CMDS) {
> > +			con_log(CL_ANN, (KERN_WARNING 
> > +			"megaraid: IOCTL packet with %d[%d:%d] being reset\n",
> > +			scb->sno, scb->dev_channel, scb->dev_target));
> >  
> > -		scp->result = (DID_RESET << 16);
> > -		scp->scsi_done(scp);
> > +			scb->status = -EFAULT;
> 
> What is the significance of -EFAULT here?  Seems inappropriate?
> 
> > @@ -2918,12 +2933,12 @@
> >  	wmb();
> >  	WRINDOOR(raid_dev, raid_dev->mbox_dma | 0x1);
> >  
> > -	for (i = 0; i < 0xFFFFF; i++) {
> > +	for (i = 0; i < 0xFFFFFF; i++) {
> >  		if (mbox->numstatus != 0xFF) break;
> >  		rmb();
> >  	}
> 
> Oh my.  That's an awfully long interrupts-off spin.  1.7e7 operations with
> an NMI watchdog timeout of five seconds - I'm surprised it doesn't trigger.
> 
> Is that reading from a PCI register there?   Or main memory?
> 
> I'm somewhat surprised that the compiler never "optimises" this into a
> lockup, actually.  That's what `volatile' is for.
> 
> Is it not possible to do this with an interrupt?
> 
> A `cpu_relax()' in that loop would help cool things down a bit.
> 
> 
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