Re: [PATCH v5 05/10] seqlock: Better document raw_write_seqcount_latch()

[Linus Torvalds]

On Mon, Apr 13, 2015 at 10:43 AM, Paul E. McKenney
<paulmck@xxxxxxxxxxxxxxxxxx> wrote:
>
> A shorthand for READ_ONCE + smp_read_barrier_depends() is the shiny
> new lockless_dereference()

Related side note - I think people should get used to seeing
"smp_load_acquire()". It has well-defined memory ordering properties
and should generally perform well on most architectures. It's (much)
stronger than lockless_dereference(), and together with
smp_store_release() you can make rather clear guarantees about passing
data locklessly from one CPU to another.

I'd like to see us use more of the pattern of

 - one thread does:

     .. allocate/create some data
      smp_store_release() to "expose it"

 - another thread does:

      smp_load_acquire() to read index/pointer/flag/whatever
      .. use the data any damn way you want ..

and we should probably aim to prefer that pattern over a lot of our
traditional memory barriers.

                          Linus
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