linux-kernel - Re: [PATCH] tty/serial: digicolor: Fix bad usage of IS_ERR

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Message-id: <56BC2DF7.20803@samsung.com>
Date:	Thu, 11 Feb 2016 07:45:11 +0100
From:	Andrzej Hajda <a.hajda@...sung.com>
To:	Guenter Roeck <linux@...ck-us.net>, Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Baruch Siach <baruch@...s.co.il>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org, Jiri Slaby <jslaby@...e.com>,
	kernel-testers@...r.kernel.org
Subject: Re: [PATCH] tty/serial: digicolor: Fix bad usage of IS_ERR_VALUE

On 02/11/2016 04:38 AM, Guenter Roeck wrote:
> On 02/10/2016 07:21 AM, Arnd Bergmann wrote:
>> On Tuesday 09 February 2016 18:37:46 Guenter Roeck wrote:
>>> On 02/09/2016 07:26 AM, Arnd Bergmann wrote:
>>>> On Tuesday 09 February 2016 07:08:59 Guenter Roeck wrote:
>>>>> IS_ERR_VALUE() assumes that its parameter is an unsigned long.
>>>>> It can not be used to check if an unsigned int reflects an error.
>>>>> Doing so can result in the following build warning.
>>>>>
>>>>> drivers/tty/serial/digicolor-usart.c: In function ‘digicolor_uart_probe’:
>>>>> include/linux/err.h:21:38: warning:
>>>>>           comparison is always false due to limited range of data type
>>>>> drivers/tty/serial/digicolor-usart.c:485:6: note:
>>>>>           in expansion of macro ‘IS_ERR_VALUE’
>>>>>
>>>>> If that warning is seen, an error return from platform_get_irq() is missed.
>>>>>
>>>>>
>>>> The patch looks correct to me, but what compiler version and which kernel
>>>> tree is it that triggered the warning?
>>>>
>>>> Andrzej Hajda just modified the definition of IS_ERR_VALUE(), and the
>>>> changes are still under discussion, but I don't see that warning with
>>>> any of the versions.
>>>>
>>> I see it with gcc 5.1 and 5.2 (and W=1). I did not see / notice Andrzej's patch.
>>>
>>> I agree that fixing the problem in IS_ERR_VALUE() is preferrable.
>>>
>>>
>> Ah, W=1 explains it. We are still debating about the proper solution. Al Viro
>> pointed out that most users of IS_ERR_VALUE() shouldn't be using it at all,
>> so your patch is probably best here after all.
>>
> Yes, after looking into it some more I agree. Coccinelle should be able to handle
> most of the conversions automatically. I actually tried to write a script, just
> for the fun of it, but it misses some of the problem cases in patch mode.
> Maybe I get it working tonight.
>
> Guenter
>

Maybe it can be helpful. The script which classifies all IS_ERR_VALUE
usages as
correct, signed, incorrect and unknown (cocci was not able to detect type).
Adding patch mode should be quite simple.

// Options: --all-includes --include
include/uapi/linux/netfilter_ipv6/ip6_tables.h --include
include/uapi/linux/netfilter_ipv4/ip_tables.h --include
include/uapi/linux/netfilter_arp/arp_tables.h --include
include/uapi/linux/netfilter/x_tables.h --include include/linux/mm_types.h

virtual context
virtual report

@r@
typedef bool, u8, u16, u32, u64, s8, s16, s32, s64, __u64, dma_addr_t,
Elf32_Addr, Elf64_Addr;
{unsigned long, size_t} ev;
{short, int, long, s16, s32, ssize_t} ew;
{char, unsigned char, unsigned short, unsigned int, long long, unsigned
long long, bool, u8, u16, u32, u64, s64, __u64, dma_addr_t, Elf32_Addr,
Elf64_Addr} ei;
expression eu;
position p;
@@

IS_ERR_VALUE(\(ev \| ew \| ei \| eu \))@p

@script:python depends on report@
p << r.p = [];
ev << r.ev = "";
ew << r.ew = "";
ei << r.ei = "";
eu << r.eu = "";
@@

t = ""
if ev: t = "correct"
if ew: t = "signed"
if ei: t = "incorrect"
if eu: t = "unknown"


e = ev + ew + ei + eu;
if t:
    msg = "WARNING: %s argument type in IS_ERR_VALUE(%s)" % (t, e)
    coccilib.report.print_report(p[0], msg)