linux-kernel - [PATCH] drivers/char/epca.c: eliminate unnecessary NULL test

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Date:	Sun, 21 Mar 2010 22:17:47 +0100 (CET)
From:	Julia Lawall <julia@...u.dk>
To:	"Digi International, Inc" <Eng.Linux@...i.com>, Eng.Linux@...i.com,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [PATCH] drivers/char/epca.c: eliminate unnecessary NULL test

From: Julia Lawall <julia@...u.dk>

Since chan0 must be a valid pointer at this point, it seems very unlikely
that ch could be NULL.  If ch could be NULL, without channel >=
bd->numports, then something else has to be done to avoid the NULL pointer
dereference in the subsequent initialization of bc.

The semantic match that finds the problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@r exists@
expression E, E1;
identifier f;
statement S1,S3;
iterator iter;
@@

if ((E == NULL && ...) || ...)
{
  ... when != false ((E == NULL && ...) || ...)
      when != true  ((E != NULL && ...) || ...)
      when != iter(E,...) S1
      when != E = E1
(
  sizeof(E->f)
|
* E->f
)
  ... when any
  return ...;
}
else S3
// </smpl>

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

---
 drivers/char/epca.c                 |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/char/epca.c b/drivers/char/epca.c
index 17b044a..ea78e6f 100644
--- a/drivers/char/epca.c
+++ b/drivers/char/epca.c
@@ -1500,9 +1500,8 @@ static void doevent(int crd)
 		lstat = readb(eventbuf + 3);
 
 		ch = chan0 + channel;
-		if ((unsigned)channel >= bd->numports || !ch)  {
-			if (channel >= bd->numports)
-				ch = chan0;
+		if ((unsigned)channel >= bd->numports)  {
+			ch = chan0;
 			bc = ch->brdchan;
 			goto next;
 		}
--
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