Messages in this thread | | | Date | Fri, 25 Nov 2016 16:32:21 +0000 | From | Mark Rutland <> | Subject | Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() |
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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: > > On Fri, Nov 25, 2016 at 04:21:39PM +0100, Dmitry Vyukov wrote: > > > > 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.
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