linux-kernel - Re: cciss

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Date:	Wed, 23 Jul 2014 10:19:11 -0500
From:	scameron@...rdog.cce.hp.com
To:	Randy Dunlap <rdunlap@...radead.org>
Cc:	linux-kernel@...r.kernel.org, xerofoify@...il.com,
	scott.benesh@...com, iss_storagedev@...com,
	michael.miller@...onical.com, scameron@...rdog.cce.hp.com
Subject: Re: cciss_scsi.c: Fix me

On Wed, Jul 23, 2014 at 08:11:33AM -0700, Randy Dunlap wrote:
> On 07/23/2014 07:41 AM, scameron@...rdog.cce.hp.com wrote:
> > On Wed, Jul 23, 2014 at 02:15:29PM +0000, Benesh, Scott wrote:
> >> From: Nick Krause [mailto:xerofoify@...il.com] 
> >> Sent: Saturday, July 19, 2014 11:51 PM
> >> To: mike.miller@...com
> >> Cc: ISS StorageDev; linux-kernel@...r.kernel.org
> >> Subject: cciss_scsi.c: Fix me
> >>
> >> Hey Mike,
> >> I seem to be hitting a fix me message in this file in function,cciss_scsi_queue_command_lck.
> >> I am wondering what you want to do when C is Null?
> >> Cheers Nick
> > 
> > Hi Nick,
> > 
> > Mike's moved on from HP to Canonical now.
> > 
> > It looks like you're running out of commands for tape drives,
> > which shouldn't ever happen, since we set 
> > 
> > 	sh->can_queue = cciss_tape_cmds;
> > 
> > and we allocate that many commands + 2....
> > 
> > scsi_cmd_stack_setup(ctlr_info_t *h, struct cciss_scsi_adapter_data_t *sa)
> > {
> >         int i;
> >         struct cciss_scsi_cmd_stack_t *stk;
> >         size_t size;
> > 
> >         stk = &sa->cmd_stack;
> >         stk->nelems = cciss_tape_cmds + 2;
> > 
> > You're apparently hitting this:
> > 
> >         spin_lock_irqsave(&h->lock, flags);
> >         c = scsi_cmd_alloc(h);
> >         spin_unlock_irqrestore(&h->lock, flags);
> >         if (c == NULL) {                        /* trouble... */
> >                 dev_warn(&h->pdev->dev, "scsi_cmd_alloc returned NULL!\n");
> >                 /* FIXME: next 3 lines are -> BAD! <- */
> >                 cmd->result = DID_NO_CONNECT << 16;
> >                 done(cmd);
> >                 return 0;
> >         }
> > 
> > which means that scsi_cmd_alloc returned NULL, which only happens
> > if the thing has run out of commands.
> > 
> > It's not obvious to me how it can be that it runs out of commands.
> > Maybe we're losing them somehow, but this has not previously been
> > a problem that I'm aware of.
> > 
> > Are you able to reproduce the problem?
> > 
> > What's going on on the system when it happens?
> > 
> > putting in a dump_stack(); near that FIXME might give a clue.
> > 
> > Which kernel are you running?
> > 
> > -- steve
> 
> Hi Steve,
> 
> You apparently have not been following the Nick saga.
> 
> Nick is using cscope to search for FIXMEs in the kernel source tree and
> then trying to generate patches to remove or 'fix' them.
> 
> He is not hitting a kernel oops or panic or bug.

Ah, ok, thanks.  That explains it, because I was pretty sure that
code is a "this will never happen" case.

-- steve

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