linux-kernel - Re: [PATCH 00/15] trivial: Drop unlikely before IS_ERR(_OR

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Message-ID: <20150731102310.GA31850@node.dhcp.inet.fi>
Date:	Fri, 31 Jul 2015 13:23:10 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>, akpm@...ux-foundation.org,
	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	Hans Ulli Kroll <ulli.kroll@...glemail.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Oleg Drokin <oleg.drokin@...el.com>,
	Andreas Dilger <andreas.dilger@...el.com>
Subject: Re: [PATCH 00/15] trivial: Drop unlikely before IS_ERR(_OR_NULL)

On Fri, Jul 31, 2015 at 11:41:09AM +0200, Vlastimil Babka wrote:
> On 07/31/2015 10:38 AM, Viresh Kumar wrote:
> >Hi,
> >
> >This cleans up the usage of IS_ERR(_OR_NULL)(), where the callers have
> >added additional unlikely compiler flag to them. It also fixes the
> >definition of IS_ERR_OR_NULL(), to use unlikely for all checks it does.
> 
> [+CC Steven Rostedt]
> 
> Any idea what the compiler does in the case of
> "if (likely(IS_ERR(...)))"? There are apparently such cases in the source.

We have two cases in code:

drivers/rtc/rtc-gemini.c:       if (likely(IS_ERR(rtc->rtc_dev)))
drivers/staging/lustre/lustre/obdclass/lu_object.c:     if (likely(IS_ERR(shadow) && PTR_ERR(shadow) == -ENOENT)) {

The first one is mistake, I think. Or do we expect rtc_device_register()
to fail?

The second is redundant. "if (PTR_ERR(shadow) == -ENOENT)" should do the
job.

-- 
 Kirill A. Shutemov
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