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Date: Thu, 22 Jun 2017 14:50:24 +0200
From: Ralf Baechle <ralf@linux-mips.org>
To: James Hogan <james.hogan@imgtec.com>
Cc: Huacai Chen <chenhc@lemote.com>, John Crispin <john@phrozen.org>,
        "Steven J . Hill" <Steven.Hill@cavium.com>,
        linux-mips@linux-mips.org, Fuxin Zhang <zhangfx@lemote.com>,
        Zhangjin Wu <wuzhangjin@gmail.com>, stable@vger.kernel.org
Subject: Re: [PATCH] MIPS: Fix a long-standing mistake in mips_atomic_set()
Message-ID: <20170622125024.GB9002@linux-mips.org>
References: <1498128345-6827-1-git-send-email-chenhc@lemote.com>
 <20170622123159.GA31455@jhogan-linux.le.imgtec.org>
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On Thu, Jun 22, 2017 at 01:31:59PM +0100, James Hogan wrote:

> Hi Huacai,
> 
> On Thu, Jun 22, 2017 at 06:45:45PM +0800, Huacai Chen wrote:
> > This mistake comes from the commit f1e39a4a616cd99 ("MIPS: Rewrite
> > sysmips(MIPS_ATOMIC_SET, ...) in C with inline assembler"). In the
> > common case 'bnez' should be 'beqz' (as same as older kernels before
> > 2.6.32), otherwise this syscall may cause an endless loop.
> > 
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Huacai Chen <chenhc@lemote.com>
> 
> Thats a coincidence. 8 years its been broken and I submitted an
> identical patch only a few weeks ago, along with some other related
> fixes:
> 
> https://patchwork.linux-mips.org/project/linux-mips/list/?series=313&state=*

I take it as a proof that everybody is using LL/SC (or the LL/SC emulation)
these days and sysmips(MIPS_ATOMIC_SET) finally has been obsoleted and is
only useful for stoneage binary compatibility.

Which is really good.  Unless people are using silly hacks such as $k0/$k1
being overwriten by exception handlers ...

  Ralf