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

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Date:	Mon, 14 Apr 2014 08:45:16 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	scameron@...rdog.cce.hp.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>
Subject: Re: [PATCH] hpsa: fix uninitialized trans_support in
 hpsa_put_ctlr_into_performant_mode()

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?

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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