From: Tejun Heo <tj@kernel.org>
To: Aleksa Sarai <cyphar@cyphar.com>
Cc: Li Zefan <lizefan@huawei.com>,
Johannes Weiner <hannes@cmpxchg.org>,
cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH] cgroup: pids: use {READ,WRITE}_ONCE for pids->limit operations
Date: Wed, 16 Oct 2019 07:27:56 -0700 [thread overview]
Message-ID: <20191016142756.GN18794@devbig004.ftw2.facebook.com> (raw)
In-Reply-To: <20191016083218.ttsaqnxpjh5i5bgv@yavin.dot.cyphar.com>
Hello, Aleksa.
On Wed, Oct 16, 2019 at 07:32:19PM +1100, Aleksa Sarai wrote:
> Maybe I'm misunderstanding Documentation/atomic_t.txt, but it looks to
> me like it's explicitly saying that I shouldn't use atomic64_t if I'm
> just using it for fetching and assignment.
Hah, where is it saying that? The alternative would be seqlock or
u64_stats or straight-up locking but idk for this atomic64_t should be
fine.
> > The non-RMW ops are (typically) regular LOADs and STOREs and are
> > canonically implemented using READ_ONCE(), WRITE_ONCE(),
> > smp_load_acquire() and smp_store_release() respectively. Therefore, if
> > you find yourself only using the Non-RMW operations of atomic_t, you
> > do not in fact need atomic_t at all and are doing it wrong.
>
> As for 64-bit on 32-bit machines -- that is a separate issue, but from
> [1] it seems to me like there are more problems that *_ONCE() fixes than
> just split reads and writes.
Your explanations are too wishy washy. If you wanna fix it, please do
it correctly. R/W ONCE isn't the right solution here.
Thanks.
--
tejun
next prev parent reply other threads:[~2019-10-16 14:28 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-12 1:05 [PATCH] cgroup: pids: use {READ,WRITE}_ONCE for pids->limit operations Aleksa Sarai
2019-10-14 15:41 ` Tejun Heo
2019-10-14 15:59 ` Aleksa Sarai
2019-10-14 16:33 ` Tejun Heo
2019-10-16 8:32 ` Aleksa Sarai
2019-10-16 14:27 ` Tejun Heo [this message]
2019-10-16 15:29 ` Aleksa Sarai
2019-10-16 15:32 ` Tejun Heo
2019-10-16 15:35 ` Aleksa Sarai
2019-10-16 15:54 ` Tejun Heo
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