Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 4 May 2023 17:41:21 +0300
From:   Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        David Howells <dhowells@redhat.com>,
        Ricardo Martinez <ricardo.martinez@linux.intel.com>
Subject: Re: [RFC PATCH 2/4] list.h: Fix parentheses around macro pointer
 parameter use
Message-ID: <ZFPEEVvHTw2uukun@smile.fi.intel.com>
References: <20230504012914.1797355-1-mathieu.desnoyers@efficios.com>
 <20230504012914.1797355-2-mathieu.desnoyers@efficios.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230504012914.1797355-2-mathieu.desnoyers@efficios.com>
Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo
Precedence: bulk

On Wed, May 03, 2023 at 09:29:12PM -0400, Mathieu Desnoyers wrote:
> Add missing parentheses around use of macro argument "pos" in those
> patterns to ensure operator precedence behaves as expected:
> 
> - typeof(*pos)
> - pos->member
> 
> Remove useless parentheses around use of macro parameter (head) in the
> following pattern:
> 
> - list_is_head(pos, (head))
> 
> Because comma is the lowest priority operator already, so the extra pair
> of parentheses is redundant.
> 
> This corrects the following usage pattern where operator precedence is
> unexpected:
> 
>   LIST_HEAD(testlist);
> 
>   struct test {
>           struct list_head node;
>           int a;
>   };
> 
>   // pos->member issue
>   void f(void)
>   {
>           struct test *t1;
>           struct test **t2 = &t1;

I'm not against the patch, but I'm in doubt, looking into this example, it's useful.
Any real use case like above in the Linux kernel, please?

>           list_for_each_entry((*t2), &testlist, node) {   /* works */
>                   //...
>           }
>           list_for_each_entry(*t2, &testlist, node) {     /* broken */
>                   //...
>           }
>   }

-- 
With Best Regards,
Andy Shevchenko