Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE()
From: Mark Rutland <mark.rutland@arm.com>
Date: 2016-11-25 16:33:12
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On Fri, Nov 25, 2016 at 05:17:09PM +0100, Peter Zijlstra wrote:
On Fri, Nov 25, 2016 at 04:10:04PM +0000, Mark Rutland wrote:quoted
On Fri, Nov 25, 2016 at 04:21:39PM +0100, Dmitry Vyukov wrote:quoted
quoted
What are use cases for such primitive that won't be OK with "read once _and_ atomically"?I have none to hand.Whatever triggers the __builtin_memcpy() paths, and even the size==8 paths on 32bit.
Lockref, per: http://lkml.iu.edu/hypermail/linux/kernel/1503.3/02294.html In that specific case, a torn value just means we'll retry until we get a non torn value, due to the cmpxchg. For that case, all we need is the value to be reloaded per invocation of READ_ONCE(). This guy seems to have the full story: http://lkml.iu.edu/hypermail/linux/kernel/1503.3/02389.html http://lkml.iu.edu/hypermail/linux/kernel/1503.3/02558.html Thanks, Mark.