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SubjectRe: 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@beardog.cce.hp.com wrote:
> > On Wed, Jul 23, 2014 at 02:15:29PM +0000, Benesh, Scott wrote:
> >> From: Nick Krause [mailto:xerofoify@gmail.com]
> >> Sent: Saturday, July 19, 2014 11:51 PM
> >> To: mike.miller@hp.com
> >> Cc: ISS StorageDev; linux-kernel@vger.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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