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From: Nam Cao <namcao@linutronix.de>
To: Larry Finger <Larry.Finger@lwfinger.net>,
	Florian Schilhabel <florian.c.schilhabel@googlemail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-staging@lists.linux.dev,
	linux-kernel@vger.kernel.org,
	Nikita Zhandarovich <n.zhandarovich@fintech.ru>
Cc: Nam Cao <namcao@linutronix.de>,
	syzbot+83763e624cfec6b462cb@syzkaller.appspotmail.com
Subject: [PATCH] staging: rtl8712: remove unnecessary alignment of pxmitpriv->pxmitbuf
Date: Sat, 25 May 2024 09:32:29 +0200
Message-Id: <20240525073229.4144612-1-namcao@linutronix.de>
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This driver wants pxmitpriv->pxmitbuf to be 4-byte aligned. This is ensured
by allocating 4 more bytes than required with kmalloc(), then do the
p = p + 4 - (p & 3) trick to make sure the pointer is 4-byte aligned.

This is unnecessary. Pointers from kmalloc() are already at least
8-byte-aligned.

Remove this alignment trick to simplify the code, and also to stop wasting
4 extra bytes of dynamic memory allocator.

This also gets rid of a (false) warning from kmemleak. This 4-byte-aligned
buffer is used to store pointers from kmalloc(). For 64-bit platforms,
pointer size is 8 bytes and kmemleak only scans for pointers in 8-byte
blocks, thus it misses the pointers stored in this 4-byte-aligned buffer
and thinks that these pointers have been leaked. This is just a false
warning, not a real problem. But still, it would be nice to get rid of
these warnings.

Reported-and-tested-by: syzbot+83763e624cfec6b462cb@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-staging/000000000000809328060a8a4c1c@google.com
Signed-off-by: Nam Cao <namcao@linutronix.de>
---
Patch sent using this driver with this patch applied.

 drivers/staging/rtl8712/rtl871x_xmit.c | 13 +++++--------
 drivers/staging/rtl8712/rtl871x_xmit.h |  1 -
 2 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/drivers/staging/rtl8712/rtl871x_xmit.c b/drivers/staging/rtl8712/rtl871x_xmit.c
index 6353dbe554d3..408616e9afcf 100644
--- a/drivers/staging/rtl8712/rtl871x_xmit.c
+++ b/drivers/staging/rtl8712/rtl871x_xmit.c
@@ -117,12 +117,9 @@ int _r8712_init_xmit_priv(struct xmit_priv *pxmitpriv,
 	/*init xmit_buf*/
 	_init_queue(&pxmitpriv->free_xmitbuf_queue);
 	_init_queue(&pxmitpriv->pending_xmitbuf_queue);
-	pxmitpriv->pallocated_xmitbuf =
-		kmalloc(NR_XMITBUFF * sizeof(struct xmit_buf) + 4, GFP_ATOMIC);
-	if (!pxmitpriv->pallocated_xmitbuf)
+	pxmitpriv->pxmitbuf = kmalloc(NR_XMITBUFF * sizeof(struct xmit_buf), GFP_ATOMIC);
+	if (!pxmitpriv->pxmitbuf)
 		goto clean_up_frame_buf;
-	pxmitpriv->pxmitbuf = pxmitpriv->pallocated_xmitbuf + 4 -
-			      ((addr_t)(pxmitpriv->pallocated_xmitbuf) & 3);
 	pxmitbuf = (struct xmit_buf *)pxmitpriv->pxmitbuf;
 	for (i = 0; i < NR_XMITBUFF; i++) {
 		INIT_LIST_HEAD(&pxmitbuf->list);
@@ -165,8 +162,8 @@ int _r8712_init_xmit_priv(struct xmit_priv *pxmitpriv,
 		for (k = 0; k < 8; k++)		/* delete xmit urb's */
 			usb_free_urb(pxmitbuf->pxmit_urb[k]);
 	}
-	kfree(pxmitpriv->pallocated_xmitbuf);
-	pxmitpriv->pallocated_xmitbuf = NULL;
+	kfree(pxmitpriv->pxmitbuf);
+	pxmitpriv->pxmitbuf = NULL;
 clean_up_frame_buf:
 	kfree(pxmitpriv->pallocated_frame_buf);
 	pxmitpriv->pallocated_frame_buf = NULL;
@@ -193,7 +190,7 @@ void _free_xmit_priv(struct xmit_priv *pxmitpriv)
 		pxmitbuf++;
 	}
 	kfree(pxmitpriv->pallocated_frame_buf);
-	kfree(pxmitpriv->pallocated_xmitbuf);
+	kfree(pxmitpriv->pxmitbuf);
 	free_hwxmits(padapter);
 }
 
diff --git a/drivers/staging/rtl8712/rtl871x_xmit.h b/drivers/staging/rtl8712/rtl871x_xmit.h
index cdcbc87a3cad..784172c385e3 100644
--- a/drivers/staging/rtl8712/rtl871x_xmit.h
+++ b/drivers/staging/rtl8712/rtl871x_xmit.h
@@ -244,7 +244,6 @@ struct	xmit_priv {
 	int cmdseq;
 	struct  __queue free_xmitbuf_queue;
 	struct  __queue pending_xmitbuf_queue;
-	u8 *pallocated_xmitbuf;
 	u8 *pxmitbuf;
 	uint free_xmitbuf_cnt;
 };
-- 
2.39.2