From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: Wei Yang <richard.weiyang-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org,
hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org,
cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 1/2] cgroup: cgroup_subsys[ssid] is never NULL
Date: Mon, 29 Nov 2021 07:35:54 -1000 [thread overview]
Message-ID: <YaUPej4QUZoFAuOM@slm.duckdns.org> (raw)
In-Reply-To: <20211127145919.31159-1-richard.weiyang-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
On Sat, Nov 27, 2021 at 02:59:18PM +0000, Wei Yang wrote:
> When the check, (ssid) < CGROUP_SUBSYS_COUNT, passed, it means
> cgroup_subsys[ssid] is defined to its proper value. It is not
> necessary to use a true to enter the loop.
...
> #define for_each_subsys(ss, ssid) \
> for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT && \
> - (((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
> + ((ss) = cgroup_subsys[ssid]); (ssid)++)
So, now the compiler has to test whether ss is NULL or not before each
iteration even though we know that it's never NULL. The whole point of that
"|| true" is telling the compiler that the pointer is never NULL.
Thanks.
--
tejun
next prev parent reply other threads:[~2021-11-29 17:35 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-27 14:59 [PATCH 1/2] cgroup: cgroup_subsys[ssid] is never NULL Wei Yang
2021-11-27 14:59 ` [PATCH 2/2] cgroup: get the wrong css for css_alloc() during cgroup_init_subsys() Wei Yang
[not found] ` <20211127145919.31159-2-richard.weiyang-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2021-11-29 17:39 ` Tejun Heo
[not found] ` <20211127145919.31159-1-richard.weiyang-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2021-11-29 17:35 ` Tejun Heo [this message]
[not found] ` <YaUPej4QUZoFAuOM-NiLfg/pYEd1N0TnZuCh8vA@public.gmane.org>
2021-11-30 0:33 ` [PATCH 1/2] cgroup: cgroup_subsys[ssid] is never NULL Wei Yang
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