Re: [Qemu-block] [PATCH] aio: Remove spurious smp_read_barrier_depends()

[Paolo Bonzini]

On 01/09/2016 16:40, Pranith Kumar wrote:
>> >
>> > bh is shared since it is equal to ctx->first_bh or
>> > ctx->first_bh->...->next.  While the compiler will always order the load
>> > of bh->next after the load of ctx->first_bh and any previous load of
>> > bh->next, this may not be the case for the processor.  Only the DEC
>> > Alpha has this behavior, but it _can_ happen.
> In that case there are a bunch of places in the same file where we
> need to insert this barrier. I also guarantee that there are many more
> files which would need this barrier if we examine closely.

If it's protected by a lock, it's not necessary.

If you don't like smp_read_barrier_depends, you can introduce a synonym
for atomic_rcu_read with another name.  But the functionality is required.

Paolo