linux-kernel - Re: [PATCH] hpsa: fix uninitialized trans_support in hpsa_put_ctlr_into_performant

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Date:	Mon, 14 Apr 2014 10:52:41 -0500
From:	scameron@...rdog.cce.hp.com
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Davidlohr Bueso <davidlohr@...com>,
	Baoquan He <bhe@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Joerg Roedel <joro@...tes.org>,
	"open list:INTEL IOMMU (VT-d)" <iommu@...ts.linux-foundation.org>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	scameron@...rdog.cce.hp.com
Subject: Re: [PATCH] hpsa: fix uninitialized trans_support in hpsa_put_ctlr_into_performant_mode()

On Mon, Apr 14, 2014 at 08:45:16AM -0700, James Bottomley wrote:
> Your subject line is very tame.  It should be the one line summary of
> why we apply the patch, so it should read something like
> 
>  hpsa: fix NULL deref in performant mode
> 
> On Thu, 2014-04-10 at 17:17 -0500, scameron@...rdog.cce.hp.com wrote:
> > Without this, you'll see a null pointer dereference in
> > hpsa_enter_performant_mode().
> 
> The description should be more comprehensible.
> 
> I'm clear that the use before initialisation is a bug ... I'm less clear
> on why it causes an oops.
> 
> > Signed-off-by: Stephen M. Cameron <scameron@...rdog.cce.hp.com>
> > ---
> >  drivers/scsi/hpsa.c |    4 ++++
> >  1 files changed, 4 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/scsi/hpsa.c b/drivers/scsi/hpsa.c
> > index 8cf4a0c..ef4dfdd 100644
> > --- a/drivers/scsi/hpsa.c
> > +++ b/drivers/scsi/hpsa.c
> > @@ -7463,6 +7463,10 @@ static void hpsa_put_ctlr_into_performant_mode(struct ctlr_info *h)
> >  	if (hpsa_simple_mode)
> >  		return;
> >  
> > +	trans_support = readl(&(h->cfgtable->TransportSupport));
> > +	if (!(trans_support & PERFORMANT_MODE))
> > +		return;
> > +
> >  	/* Check for I/O accelerator mode support */
> >  	if (trans_support & CFGTBL_Trans_io_accel1) {
> >  		transMethod |= CFGTBL_Trans_io_accel1 |
> 
> Shouldn't you be moving this check from its previous location, rather
> than adding a new one that makes the original obsolete?

Oh... I didn't notice that.   So that's what happened to that hunk.
Yes, that is what should be done.

I will resend the patch after fixing up this and the commit message.

-- steve


> 
> James
> 
> ---
> 
> diff --git a/drivers/scsi/hpsa.c b/drivers/scsi/hpsa.c
> index 8cf4a0c..9a6e4a2 100644
> --- a/drivers/scsi/hpsa.c
> +++ b/drivers/scsi/hpsa.c
> @@ -7463,6 +7463,10 @@ static void hpsa_put_ctlr_into_performant_mode(struct ctlr_info *h)
>  	if (hpsa_simple_mode)
>  		return;
>  
> +	trans_support = readl(&(h->cfgtable->TransportSupport));
> +	if (!(trans_support & PERFORMANT_MODE))
> +		return;
> +
>  	/* Check for I/O accelerator mode support */
>  	if (trans_support & CFGTBL_Trans_io_accel1) {
>  		transMethod |= CFGTBL_Trans_io_accel1 |
> @@ -7479,10 +7483,6 @@ static void hpsa_put_ctlr_into_performant_mode(struct ctlr_info *h)
>  	}
>  
>  	/* TODO, check that this next line h->nreply_queues is correct */
> -	trans_support = readl(&(h->cfgtable->TransportSupport));
> -	if (!(trans_support & PERFORMANT_MODE))
> -		return;
> -
>  	h->nreply_queues = h->msix_vector > 0 ? h->msix_vector : 1;
>  	hpsa_get_max_perf_mode_cmds(h);
>  	/* Performant mode ring buffer and supporting data structures */
> 
--
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