linux-kernel - Re: [PATCH v3] sched/numa: fix unsafe get_task_struct() in task_numa

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Message-ID: <20141022163743.GI21513@worktop.programming.kicks-ass.net>
Date:	Wed, 22 Oct 2014 18:37:43 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Kirill Tkhai <tkhai@...dex.ru>,
	Kirill Tkhai <ktkhai@...allels.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Vladimir Davydov <vdavydov@...allels.com>, cl@...ux.com
Subject: Re: [PATCH v3] sched/numa: fix unsafe get_task_struct() in
 task_numa_assign()

On Wed, Oct 22, 2014 at 06:14:50PM +0200, Oleg Nesterov wrote:
> Hmm. so perhaps I misunderstood your concern...
> 
> Do you mean that on !x86 a plain LOAD can "corrupt" the memory as it seen
> from another vaddr?

I'm not sure. Stores for sure, loads I'm not sure about.

I suspect loads are OK, the aliasing cacheline will be !modified and
therefore later eviction should discard (not write back). But like said,
I'm not at all sure.

I would hesitate to put such assumptions into generic code -- although
it appears we already have.
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