linux-kernel - [PATCH] serial: ifx6x60: avoid uninitialized variable use

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Message-ID: <3244991.qANsXoqoKs@wuerfel>
Date:	Tue, 24 Nov 2015 23:04 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	gregkh@...uxfoundation.org
Cc:	Jiri Slaby <jslaby@...e.com>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, Chen Jun <jun.d.chen@...el.com>,
	channing <chao.bi@...el.com>, Russ Gorby <russ.gorby@...el.com>,
	Vasiliy Kulikov <segoon@...nwall.com>
Subject: [PATCH] serial: ifx6x60: avoid uninitialized variable use

gcc warns about a potential use of an uninitialized variable in this driver:

drivers/tty/serial/ifx6x60.c: In function 'ifx_spi_complete':
drivers/tty/serial/ifx6x60.c:713:6: warning: 'more' may be used uninitialized in this function [-Wmaybe-uninitialized]
   if (more || ifx_dev->spi_more || queue_length > 0 ||

Unlike a lot of other such warnings, this one is correct and describes
an actual problem in the handling of the "IFX_SPI_HEADER_F" result code.

This appears to be a result from a restructuring of the driver that
dates back to before it was merged in the kernel, so it's impossible
to know where it went wrong. I also don't know what that result code
means, so I have no idea if setting 'more' to zero is the correct
solution, but at least it makes the behavior reproducible rather than
depending on whatever happens to be on the kernel stack.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
Cc everyone who contributed non-cleanup patches to this driver,
maybe someone has more insight into the operation of the driver than
I have and can comment on whether this is the right fix or not.

diff --git a/drivers/tty/serial/ifx6x60.c b/drivers/tty/serial/ifx6x60.c
index 88246f7e435a..5d18442e42ba 100644
--- a/drivers/tty/serial/ifx6x60.c
+++ b/drivers/tty/serial/ifx6x60.c
@@ -397,6 +397,7 @@ static int ifx_spi_decode_spi_header(unsigned char *buffer, int *length,
 		*received_cts = 0;
 		return IFX_SPI_HEADER_0;
 	} else if (h1 == 0xffff && h2 == 0xffff) {
+		*received_cts = 0;
 		/* spi_slave_cts remains as it was */
 		return IFX_SPI_HEADER_F;
 	}

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