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Groups > linux.kernel > #1530530
| From | "Michael S. Tsirkin" <mst@redhat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() |
| Date | 2016-11-25 22:10 +0100 |
| Message-ID | <sHvUS-5L2-33@gated-at.bofh.it> (permalink) |
| References | (5 earlier) <sHq8N-1SA-9@gated-at.bofh.it> <sHqBQ-2hw-29@gated-at.bofh.it> <sHroe-2Rp-5@gated-at.bofh.it> <sHroe-2Rp-7@gated-at.bofh.it> <sHs0W-34x-17@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Fri, Nov 25, 2016 at 05:49:45PM +0100, Christian Borntraeger wrote:
> On 11/25/2016 05:17 PM, 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.
> >
> > You could put a WARN in there to easily find them.
>
> There were several cases that I found during writing the *ONCE stuff.
> For example there are some 32bit ppc variants with 64bit PTEs. Some for
> others (I think sparc). And the mm/ code is perfectly fine with these
> PTE accesses being done NOT atomic.
In that case do we even need _ONCE at all?
Are there assumptions these are two 32 bit reads?
>
> >
> > The advantage of introducing the SINGLE_{LOAD,STORE}() helpers is that
> > they compiletime validate this the size is 'right' and can runtime check
> > alignment constraints.
> >
> > IE, they are strictly stronger than {READ,WRITE}_ONCE().
> >
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Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Mark Rutland <mark.rutland@arm.com> - 2016-11-25 12:30 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Christian Borntraeger <borntraeger@de.ibm.com> - 2016-11-25 12:40 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Mark Rutland <mark.rutland@arm.com> - 2016-11-25 13:30 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Peter Zijlstra <peterz@infradead.org> - 2016-11-25 13:50 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Peter Zijlstra <peterz@infradead.org> - 2016-11-25 13:50 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Boqun Feng <boqun.feng@gmail.com> - 2016-11-25 16:00 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Dmitry Vyukov <dvyukov@google.com> - 2016-11-25 16:30 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Mark Rutland <mark.rutland@arm.com> - 2016-11-25 17:20 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Peter Zijlstra <peterz@infradead.org> - 2016-11-25 17:20 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Mark Rutland <mark.rutland@arm.com> - 2016-11-25 17:40 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Christian Borntraeger <borntraeger@de.ibm.com> - 2016-11-25 18:00 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Mark Rutland <mark.rutland@arm.com> - 2016-11-25 18:30 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Peter Zijlstra <peterz@infradead.org> - 2016-11-25 18:50 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Christian Borntraeger <borntraeger@de.ibm.com> - 2016-11-25 19:50 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() "Michael S. Tsirkin" <mst@redhat.com> - 2016-11-25 22:10 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Christian Borntraeger <borntraeger@de.ibm.com> - 2016-11-25 22:50 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Dmitry Vyukov <dvyukov@google.com> - 2016-11-25 18:30 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Mark Rutland <mark.rutland@arm.com> - 2016-11-25 18:50 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-25 19:00 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Mark Rutland <mark.rutland@arm.com> - 2016-11-25 19:10 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-25 19:50 +0100
Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Mark Rutland <mark.rutland@arm.com> - 2016-11-25 15:40 +0100
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