Re: [PATCH RFC] libibverbs: add ARM64 memory barrier macros

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Wed, May 18, 2016 at 02:16:39PM -0700, Steve Wise wrote:
> The default generic barriers are not correct for ARM64. This results in
> data corruption.  The correct macros are lifted from the linux kernel.
> 
> Signed-off-by: Steve Wise <swise-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org>
> 
> I wonder why the linux kernel doesn't export these?  Also, if the hw
> platform is unknown, I don't think libibverbs should pick a default
> implementation that might cause data corruption.  Rather, I think it
> should just fail a compile on that platform.

These days, in user space this sort of stuff should be done following
the C11 atomic memory ordering model and not by trying to shoe-horn in
the kernel model. Then the compiler takes care of things properly.

This is using calls like atomic_store, atomic_load and
atomic_thread_fence to create the same sort of barriers.

You could probably implement the Xmbs() with variations on
atomic_thread_fence ??

Jason
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