linux-kernel - Re: [PATCH] cgroup: pids: use {READ,WRITE}

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Message-ID: <20191016155407.GP18794@devbig004.ftw2.facebook.com>
Date:   Wed, 16 Oct 2019 08:54:07 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Aleksa Sarai <cyphar@...har.com>
Cc:     Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] cgroup: pids: use {READ,WRITE}_ONCE for pids->limit
 operations

On Thu, Oct 17, 2019 at 02:35:20AM +1100, Aleksa Sarai wrote:
> > Sure, I will switch it to use atomic64_read() and atomic64_set() instead
> > if that's what you'd prefer. Though I will mention that on quite a few
> > architectures atomic64_read() is defined as:
> > 
> >   #define atomic64_read(v)        READ_ONCE((v)->counter)
> 
> Though I guess that's because on those architectures it turns out that
> READ_ONCE is properly atomic?

Oh yeah, on archs where 64bit accesses are atomic, READ_ONCE() /
WRITE_ONCE() would work here.  If the limit variable were ulong
instead of an explicit 64bit variable, RW ONCE would work too as ulong
accesses are atomic on all archs IIRC.

Thanks.

-- 
tejun