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

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Message-ID: <20160211153243.GA3076@roeck-us.net>
Date:	Thu, 11 Feb 2016 07:32:43 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Andrzej Hajda <a.hajda@...sung.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	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 Thu, Feb 11, 2016 at 07:45:11AM +0100, Andrzej Hajda wrote:
> 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 = "";

This doesn't work for me; it bails out at the assignments. If I remove
the assignments, it does not report anything.

Any idea what might be wrong ?

Thanks,
Guenter

> @@
> 
> 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)
> 
>