[PATCH 10/14] drivers/ata/libata: Move dereference after NULL test

[PATCH 10/14] drivers/ata/libata: Move dereference after NULL test

[Julia Lawall]

From: Julia Lawall <julia@diku.dk>

In each case, if the NULL test on qc is needed, then the derefernce
should be after the NULL test.

A simplified version of the semantic match that detects this problem is as
follows (http://coccinelle.lip6.fr/):

// <smpl>
@match exists@
expression x, E;
identifier fld;
@@

* x->fld
  ... when != \(x = E\|&x\)
* x == NULL
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>

---
 drivers/ata/libata-core.c           |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index b525a09..d02c95c 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4919,10 +4919,11 @@ struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev)
  */
 void ata_qc_free(struct ata_queued_cmd *qc)
 {
-	struct ata_port *ap = qc->ap;
+	struct ata_port *ap;
 	unsigned int tag;
 
 	WARN_ON_ONCE(qc == NULL); /* ata_qc_from_tag _might_ return NULL */
+	ap = qc->ap;
 
 	qc->flags = 0;
 	tag = qc->tag;
@@ -4934,11 +4935,13 @@ void ata_qc_free(struct ata_queued_cmd *qc)
 
 void __ata_qc_complete(struct ata_queued_cmd *qc)
 {
-	struct ata_port *ap = qc->ap;
-	struct ata_link *link = qc->dev->link;
+	struct ata_port *ap;
+	struct ata_link *link;
 
 	WARN_ON_ONCE(qc == NULL); /* ata_qc_from_tag _might_ return NULL */
 	WARN_ON_ONCE(!(qc->flags & ATA_QCFLAG_ACTIVE));
+	ap = qc->ap;
+	link = qc->dev->link;
 
 	if (likely(qc->flags & ATA_QCFLAG_DMAMAP))
 		ata_sg_clean(qc);

Re: [PATCH 10/14] drivers/ata/libata: Move dereference after NULL test

[Jeff Garzik]

On 10/17/2009 02:41 AM, Julia Lawall wrote:
> From: Julia Lawall<julia@diku.dk>
>
> In each case, if the NULL test on qc is needed, then the derefernce
> should be after the NULL test.
>
> A simplified version of the semantic match that detects this problem is as
> follows (http://coccinelle.lip6.fr/):
>
> //<smpl>
> @match exists@
> expression x, E;
> identifier fld;
> @@
>
> * x->fld
>    ... when != \(x = E\|&x\)
> * x == NULL
> //</smpl>
>
> Signed-off-by: Julia Lawall<julia@diku.dk>

applied