From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
To: Alexey Brodkin <Alexey.Brodkin@synopsys.com>,
"peterz@infradead.org" <peterz@infradead.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-snps-arc@lists.infradead.org"
<linux-snps-arc@lists.infradead.org>
Subject: Re: arc_usr_cmpxchg and preemption
Date: Fri, 16 Mar 2018 10:54:52 -0700 [thread overview]
Message-ID: <b0283507-5ab7-e40b-74a7-3ddebafb076d@synopsys.com> (raw)
In-Reply-To: <1521221606.4805.16.camel@synopsys.com>
On 03/16/2018 10:33 AM, Alexey Brodkin wrote:
> Hi Peter, Vineet,
>
> On Wed, 2018-03-14 at 18:53 +0100, Peter Zijlstra wrote:
>> On Wed, Mar 14, 2018 at 09:58:19AM -0700, Vineet Gupta wrote:
>>
>>> Well it is broken wrt the semantics the syscall is supposed to provide.
>>> Preemption disabling is what prevents a concurrent thread from coming in and
>>> modifying the same location (Imagine a variable which is being cmpxchg
>>> concurrently by 2 threads).
>>>
>>> One approach is to do it the MIPS way, emulate the llsc flag - set it under
>>> preemption disabled section and clear it in switch_to
>> *shudder*... just catch the -EFAULT, force the write fault and retry.
> More I look at this initially quite simple thing more it looks like
> a can of worms...
>
I'd say just bite the bullet, write the patch and we can refine it there !
-Vineet
next prev parent reply other threads:[~2018-03-16 17:54 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1521045375.11552.27.camel@synopsys.com>
2018-03-14 16:58 ` arc_usr_cmpxchg and preemption Vineet Gupta
2018-03-14 16:58 ` Vineet Gupta
2018-03-14 17:53 ` Peter Zijlstra
2018-03-14 17:53 ` Peter Zijlstra
2018-03-14 18:20 ` Peter Zijlstra
2018-03-14 18:20 ` Peter Zijlstra
2018-03-14 20:38 ` Alexey Brodkin
2018-03-14 20:38 ` Alexey Brodkin
2018-03-14 20:55 ` Vineet Gupta
2018-03-14 20:55 ` Vineet Gupta
2018-03-15 8:18 ` Peter Zijlstra
2018-03-15 8:18 ` Peter Zijlstra
2018-03-15 9:12 ` Alexey Brodkin
2018-03-15 9:12 ` Alexey Brodkin
2018-03-15 11:28 ` Peter Zijlstra
2018-03-15 11:28 ` Peter Zijlstra
2018-03-15 19:03 ` Alexey Brodkin
2018-03-15 19:03 ` Alexey Brodkin
2018-03-16 7:55 ` Peter Zijlstra
2018-03-16 7:55 ` Peter Zijlstra
2018-03-16 18:12 ` Max Filippov
2018-03-16 18:12 ` Max Filippov
2018-03-16 17:33 ` Alexey Brodkin
2018-03-16 17:33 ` Alexey Brodkin
2018-03-16 17:54 ` Vineet Gupta [this message]
2018-03-16 17:54 ` Vineet Gupta
2018-03-16 17:58 ` Peter Zijlstra
2018-03-16 17:58 ` Peter Zijlstra
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