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Message-ID: <94f293d3d31e9f686e601e2e3c972ae371a40585.camel@perches.com>
Subject: Re: [PATCH] checkpatch: check for nested (un)?likely calls
From:   Joe Perches <joe@perches.com>
To:     Denis Efremov <efremov@linux.com>,
        Andy Whitcroft <apw@canonical.com>
Cc:     linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>
Date:   Tue, 27 Aug 2019 10:21:01 -0700
In-Reply-To: <20190827165515.21668-1-efremov@linux.com>
References: <20190827165515.21668-1-efremov@linux.com>
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On Tue, 2019-08-27 at 19:55 +0300, Denis Efremov wrote:
> IS_ERR, IS_ERR_OR_NULL, IS_ERR_VALUE already contain unlikely optimization
> internally. Thus, there is no point in calling these functions under
> likely/unlikely.
> 
> This check is based on the coccinelle rule developed by Enrico Weigelt
> https://lore.kernel.org/lkml/1559767582-11081-1-git-send-email-info@metux.net/
[]
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -6480,6 +6480,13 @@ sub process {
>  			     "Using $1 should generally have parentheses around the comparison\n" . $herecurr);
>  		}
>  
> +# nested likely/unlikely calls
> +		if ($perl_version_ok &&
> +		    $line =~ /\b(?:(?:un)?likely)\s*\(!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?)\s*${balanced_parens}\s*\)/) {
> +			WARN("LIKELY_MISUSE",
> +			     "nested (un)?likely calls, unlikely already used in $1 internally\n" . $herecurr);
> +		}
> +

Couple things:

1:

Are you going to submit patches for the just 10 instances that exist?

$ git grep -P -n '\b(?:(?:un)?likely)\s*\(!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?)\s*\([^\)]+\)\s*\)'
arch/x86/kernel/irq.c:246:      if (likely(!IS_ERR_OR_NULL(desc))) {
drivers/infiniband/hw/hfi1/verbs.c:1044:        if (unlikely(IS_ERR_OR_NULL(pbuf))) {
drivers/input/mouse/alps.c:1479:        } else if (unlikely(IS_ERR_OR_NULL(priv->dev3))) {
fs/ntfs/mft.c:74:       if (likely(!IS_ERR(page))) {
fs/ntfs/mft.c:157:      if (likely(!IS_ERR(m)))
fs/ntfs/mft.c:274:              if (likely(!IS_ERR(m))) {
fs/ntfs/mft.c:1779:             if (likely(!IS_ERR(rl2)))
fs/ntfs/namei.c:118:            if (likely(!IS_ERR(dent_inode))) {
fs/ntfs/runlist.c:954:  if (likely(!IS_ERR(old_rl)))
include/net/udp.h:483:  if (unlikely(IS_ERR_OR_NULL(segs))) {

2:

This will not warn about code like:

fs/ntfs/mft.c:  if (unlikely(IS_ERR(rl) || !rl->length || rl->lcn < 0)) {

that could probably be better written as:

		if (IS_ERR(rl) || unlikely(!rl->length || rl->lcn < 0)) {