linux-kernel - Re: [PATCH] llist: Put parentheses around parameters of llist_for_each_entry

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Date:   Tue, 26 Sep 2017 16:14:16 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     박병철/선임연구원/SW Platform(연)AOT팀(byungchul.park@....com) 
        <byungchul.park@....com>
Cc:     "Huang\, Ying" <ying.huang@...el.com>,
        "peterz\@infradead.org" <peterz@...radead.org>,
        "mingo\@kernel.org" <mingo@...nel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel-team\@lge.com" <kernel-team@....com>
Subject: Re: [PATCH] llist: Put parentheses around parameters of llist_for_each_entry_safe()

"박병철/선임연구원/SW Platform(연)AOT팀(byungchul.park@....com)"
<byungchul.park@....com> writes:

>> -----Original Message-----
>> From: Huang, Ying [mailto:ying.huang@...el.com]
>> Sent: Tuesday, September 26, 2017 4:02 PM
>> To: Byungchul Park
>> Cc: peterz@...radead.org; mingo@...nel.org; linux-kernel@...r.kernel.org;
>> kernel-team@....com; ying.huang@...el.com
>> Subject: Re: [PATCH] llist: Put parentheses around parameters of
>> llist_for_each_entry_safe()
>> 
>> Hi, Byungchul,
>> 
>> Byungchul Park <byungchul.park@....com> writes:
>> 
>> > It would be somewhat safer to put parentheses around parameters of
>> > a macro with parameters. Put it.
>> >
>> > Signed-off-by: Byungchul Park <byungchul.park@....com>
>> > ---
>> >  include/linux/llist.h | 6 +++---
>> >  1 file changed, 3 insertions(+), 3 deletions(-)
>> >
>> > diff --git a/include/linux/llist.h b/include/linux/llist.h
>> > index 1957635..e280b297 100644
>> > --- a/include/linux/llist.h
>> > +++ b/include/linux/llist.h
>> > @@ -183,10 +183,10 @@ static inline void init_llist_head(struct llist_head *list)
>> >   * reverse the order by yourself before traversing.
>> >   */
>> >  #define llist_for_each_entry_safe(pos, n, node, member)
>> 	       \
>> > -	for (pos = llist_entry((node), typeof(*pos), member);		       \
>> > +	for ((pos) = llist_entry((node), typeof(*(pos)), member);		       \
>> >  	     member_address_is_nonnull(pos, member) &&
>> 	       \
>> > -	        (n = llist_entry(pos->member.next, typeof(*n), member), true); \
>> > -	     pos = n)
>> > +	        ((n) = llist_entry((pos)->member.next, typeof(*(n)), member), true);
>> \
>> > +	     (pos) = (n))
>> >
>> >  /**
>> >   * llist_empty - tests whether a lock-less list is empty
>> 
>> The original code follows the style of list_for_each_entry_safe().  The
>
> Hello Huang,
>
> I don’t see what you say here exactly, but let me note that all llist macros
> are safe except the llist_for_each_entry_safe().
>
>> parameters "pos" and "n" must be variable.  Because list_xxx family
>> functions work well so far, I think we needn't to change it too.
>
> I see. I don't want to argue much wrt such a trivial thing but I think
> it would be better to fix it since the fix is fairly simple and clear. 
> However, it's ok if the fix introduces a bad thing at least.

Yes, it's simple.  But I don't think it helps too.  Considering that
list family functions with same style have no issues.

Best Regards,
Huang, Ying